From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-5.9 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id ACD58C2B9F4 for ; Thu, 17 Jun 2021 06:05:10 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 8328B61351 for ; Thu, 17 Jun 2021 06:05:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229565AbhFQGHQ (ORCPT ); Thu, 17 Jun 2021 02:07:16 -0400 Received: from mail.kernel.org ([198.145.29.99]:60258 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229515AbhFQGHO (ORCPT ); Thu, 17 Jun 2021 02:07:14 -0400 Received: by mail.kernel.org (Postfix) with ESMTPSA id BC0B361241; Thu, 17 Jun 2021 06:05:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1623909907; bh=kjP9+T+FmEwuicRXDVHEk8Z4tkoS0foRxBhRhF9EAqw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IA8d5JaiFMvog9SZe7/L871QLI+SQWNyMXLymWGi3ojDYyeU3RoBRDZSMY3cJkeOO WIg9KihxcaCD0QN4jZhXOB0sFCDIeS9HeWJL7bjZY1sA2LBdtH2DzctLBv1/hhGOjQ b0qwQ03b10MYLb7x1u/SQg8jB1u2z11fol2fq2nE= Date: Thu, 17 Jun 2021 08:05:03 +0200 From: Greg KH To: Jing Zhang Cc: KVM , KVMARM , LinuxMIPS , KVMPPC , LinuxS390 , Linuxkselftest , Paolo Bonzini , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , Will Deacon , Huacai Chen , Aleksandar Markovic , Thomas Bogendoerfer , Paul Mackerras , Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Sean Christopherson , Vitaly Kuznetsov , Jim Mattson , Peter Shier , Oliver Upton , David Rientjes , Emanuele Giuseppe Esposito , David Matlack , Ricardo Koller , Krish Sadhukhan , Fuad Tabba Subject: Re: [PATCH v10 3/5] KVM: stats: Add documentation for binary statistics interface Message-ID: References: <20210617044146.2667540-1-jingzhangos@google.com> <20210617044146.2667540-4-jingzhangos@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20210617044146.2667540-4-jingzhangos@google.com> Precedence: bulk List-ID: X-Mailing-List: linux-mips@vger.kernel.org On Thu, Jun 17, 2021 at 04:41:44AM +0000, Jing Zhang wrote: > +The file descriptor can be used to read VM/vCPU statistics data in binary > +format. The file data is organized into three blocks as below: > ++-------------+ > +| Header | > ++-------------+ > +| Descriptors | > ++-------------+ > +| Stats Data | > ++-------------+ > + > +The Header block is always at the start of the file. It is only needed to be > +read one time for the lifetime of the file descriptor. > +It is in the form of ``struct kvm_stats_header`` as below:: > + > + #define KVM_STATS_ID_MAXLEN 64 > + > + struct kvm_stats_header { > + __u32 name_size; > + __u32 count; > + __u32 desc_offset; > + __u32 data_offset; > + char id[0]; > + }; So you have no idea the size of the whole header when reading it? That feels odd, are you sure it's not needed? > +The ``id`` field is identification for the corresponding KVM statistics. For > +VM statistics, it is in the form of "kvm-{kvm pid}", like "kvm-12345". For > +VCPU statistics, it is in the form of "kvm-{kvm pid}/vcpu-{vcpu id}", like > +"kvm-12345/vcpu-12". Why do you have "name_size" but not "id_size"? And is this a \0 terminated string? If so, please state it here. And what is the max size of this string? And again, should it be [], not [0]? Will the header be padded out to any specific byte boundry (4/8/32/whatever) before the other headers? > + > +The ``name_size`` field is the size (byte) of the statistics name string s/byte/in bytes/ > +(including trailing '\0') appended to the end of every statistics descriptor. > + > +The ``count`` field is the number of statistics. > + > +The ``desc_offset`` field is the offset of the Descriptors block from the start > +of the file indicated by the file descriptor. > + > +The ``data_offset`` field is the offset of the Stats Data block from the start > +of the file indicated by the file descriptor. > + > +The Descriptors block is only needed to be read once for the lifetime of the > +file descriptor. It is an array of ``struct kvm_stats_desc`` as shown in > +below code block:: > + > + #define KVM_STATS_TYPE_SHIFT 0 > + #define KVM_STATS_TYPE_MASK (0xF << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_CUMULATIVE (0x0 << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_INSTANT (0x1 << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_MAX KVM_STATS_TYPE_INSTANT > + > + #define KVM_STATS_UNIT_SHIFT 4 > + #define KVM_STATS_UNIT_MASK (0xF << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_NONE (0x0 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_BYTES (0x1 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_SECONDS (0x2 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_CYCLES (0x3 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_MAX KVM_STATS_UNIT_CYCLES > + > + #define KVM_STATS_BASE_SHIFT 8 > + #define KVM_STATS_BASE_MASK (0xF << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_POW10 (0x0 << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_POW2 (0x1 << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_MAX KVM_STATS_BASE_POW2 > + > + struct kvm_stats_desc { > + __u32 flags; > + __s16 exponent; > + __u16 size; > + __u32 offset; > + __u32 unused; > + char name[0]; > + }; > + > +The ``flags`` field contains the type and unit of the statistics data described > +by this descriptor. The following flags are supported: > + > +Bits 0-3 of ``flags`` encode the type: > + * ``KVM_STATS_TYPE_CUMULATIVE`` > + The statistics data is cumulative. The value of data can only be increased. > + Most of the counters used in KVM are of this type. > + The corresponding ``count`` field for this type is always 1. > + * ``KVM_STATS_TYPE_INSTANT`` > + The statistics data is instantaneous. Its value can be increased or > + decreased. This type is usually used as a measurement of some resources, > + like the number of dirty pages, the number of large pages, etc. > + The corresponding ``count`` field for this type is always 1. > + > +Bits 4-7 of ``flags`` encode the unit: > + * ``KVM_STATS_UNIT_NONE`` > + There is no unit for the value of statistics data. This usually means that > + the value is a simple counter of an event. > + * ``KVM_STATS_UNIT_BYTES`` > + It indicates that the statistics data is used to measure memory size, in the > + unit of Byte, KiByte, MiByte, GiByte, etc. The unit of the data is > + determined by the ``exponent`` field in the descriptor. The > + ``KVM_STATS_BASE_POW2`` flag is valid in this case. The unit of the data is > + determined by ``pow(2, exponent)``. For example, if value is 10, > + ``exponent`` is 20, which means the unit of statistics data is MiByte, we > + can get the statistics data in the unit of Byte by > + ``value * pow(2, exponent) = 10 * pow(2, 20) = 10 MiByte`` which is > + 10 * 1024 * 1024 Bytes. > + * ``KVM_STATS_UNIT_SECONDS`` > + It indicates that the statistics data is used to measure time/latency, in > + the unit of nanosecond, microsecond, millisecond and second. The unit of the > + data is determined by the ``exponent`` field in the descriptor. The > + ``KVM_STATS_BASE_POW10`` flag is valid in this case. The unit of the data > + is determined by ``pow(10, exponent)``. For example, if value is 2000000, > + ``exponent`` is -6, which means the unit of statistics data is microsecond, > + we can get the statistics data in the unit of second by > + ``value * pow(10, exponent) = 2000000 * pow(10, -6) = 2 seconds``. > + * ``KVM_STATS_UNIT_CYCLES`` > + It indicates that the statistics data is used to measure CPU clock cycles. > + The ``KVM_STATS_BASE_POW10`` flag is valid in this case. For example, if > + value is 200, ``exponent`` is 4, we can get the number of CPU clock cycles > + by ``value * pow(10, exponent) = 200 * pow(10, 4) = 2000000``. > + > +Bits 8-11 of ``flags`` encode the base: > + * ``KVM_STATS_BASE_POW10`` > + The scale is based on power of 10. It is used for measurement of time and > + CPU clock cycles. > + * ``KVM_STATS_BASE_POW2`` > + The scale is based on power of 2. It is used for measurement of memory size. > + > +The ``exponent`` field is the scale of corresponding statistics data. For > +example, if the unit is ``KVM_STATS_UNIT_BYTES``, the base is > +``KVM_STATS_BASE_POW2``, the ``exponent`` is 10, then we know that the real > +unit of the statistics data is KBytes a.k.a pow(2, 10) = 1024 bytes. Might also want to show a negative example here for exponent, like you show above for time. > + > +The ``size`` field is the number of values (u64) of this statistics data. Its > +value is usually 1 for most of simple statistics. What does "u64" mean here? thanks, greg k-h From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-3.6 required=3.0 tests=BAYES_00,DKIM_INVALID, DKIM_SIGNED,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_HELO_NONE, SPF_PASS autolearn=no autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5AAF0C2B9F4 for ; Thu, 17 Jun 2021 06:05:13 +0000 (UTC) Received: from mm01.cs.columbia.edu (mm01.cs.columbia.edu [128.59.11.253]) by mail.kernel.org (Postfix) with ESMTP id C008861351 for ; Thu, 17 Jun 2021 06:05:12 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org C008861351 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linuxfoundation.org Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=kvmarm-bounces@lists.cs.columbia.edu Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 5F18440762; Thu, 17 Jun 2021 02:05:12 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Authentication-Results: mm01.cs.columbia.edu (amavisd-new); dkim=softfail (fail, message has been altered) header.i=@linuxfoundation.org Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id SR3uO0QVey48; Thu, 17 Jun 2021 02:05:11 -0400 (EDT) Received: from mm01.cs.columbia.edu (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 19BF449F8F; Thu, 17 Jun 2021 02:05:11 -0400 (EDT) Received: from localhost (localhost [127.0.0.1]) by mm01.cs.columbia.edu (Postfix) with ESMTP id 1E2EA404F8 for ; Thu, 17 Jun 2021 02:05:10 -0400 (EDT) X-Virus-Scanned: at lists.cs.columbia.edu Received: from mm01.cs.columbia.edu ([127.0.0.1]) by localhost (mm01.cs.columbia.edu [127.0.0.1]) (amavisd-new, port 10024) with ESMTP id m9GflETnE4Qp for ; Thu, 17 Jun 2021 02:05:08 -0400 (EDT) Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by mm01.cs.columbia.edu (Postfix) with ESMTPS id A7F9A40762 for ; Thu, 17 Jun 2021 02:05:08 -0400 (EDT) Received: by mail.kernel.org (Postfix) with ESMTPSA id BC0B361241; Thu, 17 Jun 2021 06:05:06 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=linuxfoundation.org; s=korg; t=1623909907; bh=kjP9+T+FmEwuicRXDVHEk8Z4tkoS0foRxBhRhF9EAqw=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=IA8d5JaiFMvog9SZe7/L871QLI+SQWNyMXLymWGi3ojDYyeU3RoBRDZSMY3cJkeOO WIg9KihxcaCD0QN4jZhXOB0sFCDIeS9HeWJL7bjZY1sA2LBdtH2DzctLBv1/hhGOjQ b0qwQ03b10MYLb7x1u/SQg8jB1u2z11fol2fq2nE= Date: Thu, 17 Jun 2021 08:05:03 +0200 From: Greg KH To: Jing Zhang Subject: Re: [PATCH v10 3/5] KVM: stats: Add documentation for binary statistics interface Message-ID: References: <20210617044146.2667540-1-jingzhangos@google.com> <20210617044146.2667540-4-jingzhangos@google.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <20210617044146.2667540-4-jingzhangos@google.com> Cc: KVM , David Hildenbrand , Paul Mackerras , Linuxkselftest , Claudio Imbrenda , Will Deacon , KVMARM , Emanuele Giuseppe Esposito , LinuxS390 , Janosch Frank , Marc Zyngier , Huacai Chen , Christian Borntraeger , Aleksandar Markovic , David Rientjes , KVMPPC , Krish Sadhukhan , David Matlack , Jim Mattson , Thomas Bogendoerfer , Sean Christopherson , Cornelia Huck , Peter Shier , LinuxMIPS , Paolo Bonzini , Vitaly Kuznetsov X-BeenThere: kvmarm@lists.cs.columbia.edu X-Mailman-Version: 2.1.14 Precedence: list List-Id: Where KVM/ARM decisions are made List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Errors-To: kvmarm-bounces@lists.cs.columbia.edu Sender: kvmarm-bounces@lists.cs.columbia.edu On Thu, Jun 17, 2021 at 04:41:44AM +0000, Jing Zhang wrote: > +The file descriptor can be used to read VM/vCPU statistics data in binary > +format. The file data is organized into three blocks as below: > ++-------------+ > +| Header | > ++-------------+ > +| Descriptors | > ++-------------+ > +| Stats Data | > ++-------------+ > + > +The Header block is always at the start of the file. It is only needed to be > +read one time for the lifetime of the file descriptor. > +It is in the form of ``struct kvm_stats_header`` as below:: > + > + #define KVM_STATS_ID_MAXLEN 64 > + > + struct kvm_stats_header { > + __u32 name_size; > + __u32 count; > + __u32 desc_offset; > + __u32 data_offset; > + char id[0]; > + }; So you have no idea the size of the whole header when reading it? That feels odd, are you sure it's not needed? > +The ``id`` field is identification for the corresponding KVM statistics. For > +VM statistics, it is in the form of "kvm-{kvm pid}", like "kvm-12345". For > +VCPU statistics, it is in the form of "kvm-{kvm pid}/vcpu-{vcpu id}", like > +"kvm-12345/vcpu-12". Why do you have "name_size" but not "id_size"? And is this a \0 terminated string? If so, please state it here. And what is the max size of this string? And again, should it be [], not [0]? Will the header be padded out to any specific byte boundry (4/8/32/whatever) before the other headers? > + > +The ``name_size`` field is the size (byte) of the statistics name string s/byte/in bytes/ > +(including trailing '\0') appended to the end of every statistics descriptor. > + > +The ``count`` field is the number of statistics. > + > +The ``desc_offset`` field is the offset of the Descriptors block from the start > +of the file indicated by the file descriptor. > + > +The ``data_offset`` field is the offset of the Stats Data block from the start > +of the file indicated by the file descriptor. > + > +The Descriptors block is only needed to be read once for the lifetime of the > +file descriptor. It is an array of ``struct kvm_stats_desc`` as shown in > +below code block:: > + > + #define KVM_STATS_TYPE_SHIFT 0 > + #define KVM_STATS_TYPE_MASK (0xF << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_CUMULATIVE (0x0 << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_INSTANT (0x1 << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_MAX KVM_STATS_TYPE_INSTANT > + > + #define KVM_STATS_UNIT_SHIFT 4 > + #define KVM_STATS_UNIT_MASK (0xF << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_NONE (0x0 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_BYTES (0x1 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_SECONDS (0x2 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_CYCLES (0x3 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_MAX KVM_STATS_UNIT_CYCLES > + > + #define KVM_STATS_BASE_SHIFT 8 > + #define KVM_STATS_BASE_MASK (0xF << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_POW10 (0x0 << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_POW2 (0x1 << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_MAX KVM_STATS_BASE_POW2 > + > + struct kvm_stats_desc { > + __u32 flags; > + __s16 exponent; > + __u16 size; > + __u32 offset; > + __u32 unused; > + char name[0]; > + }; > + > +The ``flags`` field contains the type and unit of the statistics data described > +by this descriptor. The following flags are supported: > + > +Bits 0-3 of ``flags`` encode the type: > + * ``KVM_STATS_TYPE_CUMULATIVE`` > + The statistics data is cumulative. The value of data can only be increased. > + Most of the counters used in KVM are of this type. > + The corresponding ``count`` field for this type is always 1. > + * ``KVM_STATS_TYPE_INSTANT`` > + The statistics data is instantaneous. Its value can be increased or > + decreased. This type is usually used as a measurement of some resources, > + like the number of dirty pages, the number of large pages, etc. > + The corresponding ``count`` field for this type is always 1. > + > +Bits 4-7 of ``flags`` encode the unit: > + * ``KVM_STATS_UNIT_NONE`` > + There is no unit for the value of statistics data. This usually means that > + the value is a simple counter of an event. > + * ``KVM_STATS_UNIT_BYTES`` > + It indicates that the statistics data is used to measure memory size, in the > + unit of Byte, KiByte, MiByte, GiByte, etc. The unit of the data is > + determined by the ``exponent`` field in the descriptor. The > + ``KVM_STATS_BASE_POW2`` flag is valid in this case. The unit of the data is > + determined by ``pow(2, exponent)``. For example, if value is 10, > + ``exponent`` is 20, which means the unit of statistics data is MiByte, we > + can get the statistics data in the unit of Byte by > + ``value * pow(2, exponent) = 10 * pow(2, 20) = 10 MiByte`` which is > + 10 * 1024 * 1024 Bytes. > + * ``KVM_STATS_UNIT_SECONDS`` > + It indicates that the statistics data is used to measure time/latency, in > + the unit of nanosecond, microsecond, millisecond and second. The unit of the > + data is determined by the ``exponent`` field in the descriptor. The > + ``KVM_STATS_BASE_POW10`` flag is valid in this case. The unit of the data > + is determined by ``pow(10, exponent)``. For example, if value is 2000000, > + ``exponent`` is -6, which means the unit of statistics data is microsecond, > + we can get the statistics data in the unit of second by > + ``value * pow(10, exponent) = 2000000 * pow(10, -6) = 2 seconds``. > + * ``KVM_STATS_UNIT_CYCLES`` > + It indicates that the statistics data is used to measure CPU clock cycles. > + The ``KVM_STATS_BASE_POW10`` flag is valid in this case. For example, if > + value is 200, ``exponent`` is 4, we can get the number of CPU clock cycles > + by ``value * pow(10, exponent) = 200 * pow(10, 4) = 2000000``. > + > +Bits 8-11 of ``flags`` encode the base: > + * ``KVM_STATS_BASE_POW10`` > + The scale is based on power of 10. It is used for measurement of time and > + CPU clock cycles. > + * ``KVM_STATS_BASE_POW2`` > + The scale is based on power of 2. It is used for measurement of memory size. > + > +The ``exponent`` field is the scale of corresponding statistics data. For > +example, if the unit is ``KVM_STATS_UNIT_BYTES``, the base is > +``KVM_STATS_BASE_POW2``, the ``exponent`` is 10, then we know that the real > +unit of the statistics data is KBytes a.k.a pow(2, 10) = 1024 bytes. Might also want to show a negative example here for exponent, like you show above for time. > + > +The ``size`` field is the number of values (u64) of this statistics data. Its > +value is usually 1 for most of simple statistics. What does "u64" mean here? thanks, greg k-h _______________________________________________ kvmarm mailing list kvmarm@lists.cs.columbia.edu https://lists.cs.columbia.edu/mailman/listinfo/kvmarm From mboxrd@z Thu Jan 1 00:00:00 1970 From: Greg KH Date: Thu, 17 Jun 2021 06:05:03 +0000 Subject: Re: [PATCH v10 3/5] KVM: stats: Add documentation for binary statistics interface Message-Id: List-Id: References: <20210617044146.2667540-1-jingzhangos@google.com> <20210617044146.2667540-4-jingzhangos@google.com> In-Reply-To: <20210617044146.2667540-4-jingzhangos@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit To: Jing Zhang Cc: KVM , KVMARM , LinuxMIPS , KVMPPC , LinuxS390 , Linuxkselftest , Paolo Bonzini , Marc Zyngier , James Morse , Julien Thierry , Suzuki K Poulose , Will Deacon , Huacai Chen , Aleksandar Markovic , Thomas Bogendoerfer , Paul Mackerras , Christian Borntraeger , Janosch Frank , David Hildenbrand , Cornelia Huck , Claudio Imbrenda , Sean Christopherson , Vitaly Kuznetsov , Jim Mattson , Peter Shier , Oliver Upton , David Rientjes , Emanuele Giuseppe Esposito , David Matlack , Ricardo Koller , Krish Sadhukhan , Fuad Tabba On Thu, Jun 17, 2021 at 04:41:44AM +0000, Jing Zhang wrote: > +The file descriptor can be used to read VM/vCPU statistics data in binary > +format. The file data is organized into three blocks as below: > ++-------------+ > +| Header | > ++-------------+ > +| Descriptors | > ++-------------+ > +| Stats Data | > ++-------------+ > + > +The Header block is always at the start of the file. It is only needed to be > +read one time for the lifetime of the file descriptor. > +It is in the form of ``struct kvm_stats_header`` as below:: > + > + #define KVM_STATS_ID_MAXLEN 64 > + > + struct kvm_stats_header { > + __u32 name_size; > + __u32 count; > + __u32 desc_offset; > + __u32 data_offset; > + char id[0]; > + }; So you have no idea the size of the whole header when reading it? That feels odd, are you sure it's not needed? > +The ``id`` field is identification for the corresponding KVM statistics. For > +VM statistics, it is in the form of "kvm-{kvm pid}", like "kvm-12345". For > +VCPU statistics, it is in the form of "kvm-{kvm pid}/vcpu-{vcpu id}", like > +"kvm-12345/vcpu-12". Why do you have "name_size" but not "id_size"? And is this a \0 terminated string? If so, please state it here. And what is the max size of this string? And again, should it be [], not [0]? Will the header be padded out to any specific byte boundry (4/8/32/whatever) before the other headers? > + > +The ``name_size`` field is the size (byte) of the statistics name string s/byte/in bytes/ > +(including trailing '\0') appended to the end of every statistics descriptor. > + > +The ``count`` field is the number of statistics. > + > +The ``desc_offset`` field is the offset of the Descriptors block from the start > +of the file indicated by the file descriptor. > + > +The ``data_offset`` field is the offset of the Stats Data block from the start > +of the file indicated by the file descriptor. > + > +The Descriptors block is only needed to be read once for the lifetime of the > +file descriptor. It is an array of ``struct kvm_stats_desc`` as shown in > +below code block:: > + > + #define KVM_STATS_TYPE_SHIFT 0 > + #define KVM_STATS_TYPE_MASK (0xF << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_CUMULATIVE (0x0 << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_INSTANT (0x1 << KVM_STATS_TYPE_SHIFT) > + #define KVM_STATS_TYPE_MAX KVM_STATS_TYPE_INSTANT > + > + #define KVM_STATS_UNIT_SHIFT 4 > + #define KVM_STATS_UNIT_MASK (0xF << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_NONE (0x0 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_BYTES (0x1 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_SECONDS (0x2 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_CYCLES (0x3 << KVM_STATS_UNIT_SHIFT) > + #define KVM_STATS_UNIT_MAX KVM_STATS_UNIT_CYCLES > + > + #define KVM_STATS_BASE_SHIFT 8 > + #define KVM_STATS_BASE_MASK (0xF << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_POW10 (0x0 << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_POW2 (0x1 << KVM_STATS_BASE_SHIFT) > + #define KVM_STATS_BASE_MAX KVM_STATS_BASE_POW2 > + > + struct kvm_stats_desc { > + __u32 flags; > + __s16 exponent; > + __u16 size; > + __u32 offset; > + __u32 unused; > + char name[0]; > + }; > + > +The ``flags`` field contains the type and unit of the statistics data described > +by this descriptor. The following flags are supported: > + > +Bits 0-3 of ``flags`` encode the type: > + * ``KVM_STATS_TYPE_CUMULATIVE`` > + The statistics data is cumulative. The value of data can only be increased. > + Most of the counters used in KVM are of this type. > + The corresponding ``count`` field for this type is always 1. > + * ``KVM_STATS_TYPE_INSTANT`` > + The statistics data is instantaneous. Its value can be increased or > + decreased. This type is usually used as a measurement of some resources, > + like the number of dirty pages, the number of large pages, etc. > + The corresponding ``count`` field for this type is always 1. > + > +Bits 4-7 of ``flags`` encode the unit: > + * ``KVM_STATS_UNIT_NONE`` > + There is no unit for the value of statistics data. This usually means that > + the value is a simple counter of an event. > + * ``KVM_STATS_UNIT_BYTES`` > + It indicates that the statistics data is used to measure memory size, in the > + unit of Byte, KiByte, MiByte, GiByte, etc. The unit of the data is > + determined by the ``exponent`` field in the descriptor. The > + ``KVM_STATS_BASE_POW2`` flag is valid in this case. The unit of the data is > + determined by ``pow(2, exponent)``. For example, if value is 10, > + ``exponent`` is 20, which means the unit of statistics data is MiByte, we > + can get the statistics data in the unit of Byte by > + ``value * pow(2, exponent) = 10 * pow(2, 20) = 10 MiByte`` which is > + 10 * 1024 * 1024 Bytes. > + * ``KVM_STATS_UNIT_SECONDS`` > + It indicates that the statistics data is used to measure time/latency, in > + the unit of nanosecond, microsecond, millisecond and second. The unit of the > + data is determined by the ``exponent`` field in the descriptor. The > + ``KVM_STATS_BASE_POW10`` flag is valid in this case. The unit of the data > + is determined by ``pow(10, exponent)``. For example, if value is 2000000, > + ``exponent`` is -6, which means the unit of statistics data is microsecond, > + we can get the statistics data in the unit of second by > + ``value * pow(10, exponent) = 2000000 * pow(10, -6) = 2 seconds``. > + * ``KVM_STATS_UNIT_CYCLES`` > + It indicates that the statistics data is used to measure CPU clock cycles. > + The ``KVM_STATS_BASE_POW10`` flag is valid in this case. For example, if > + value is 200, ``exponent`` is 4, we can get the number of CPU clock cycles > + by ``value * pow(10, exponent) = 200 * pow(10, 4) = 2000000``. > + > +Bits 8-11 of ``flags`` encode the base: > + * ``KVM_STATS_BASE_POW10`` > + The scale is based on power of 10. It is used for measurement of time and > + CPU clock cycles. > + * ``KVM_STATS_BASE_POW2`` > + The scale is based on power of 2. It is used for measurement of memory size. > + > +The ``exponent`` field is the scale of corresponding statistics data. For > +example, if the unit is ``KVM_STATS_UNIT_BYTES``, the base is > +``KVM_STATS_BASE_POW2``, the ``exponent`` is 10, then we know that the real > +unit of the statistics data is KBytes a.k.a pow(2, 10) = 1024 bytes. Might also want to show a negative example here for exponent, like you show above for time. > + > +The ``size`` field is the number of values (u64) of this statistics data. Its > +value is usually 1 for most of simple statistics. What does "u64" mean here? thanks, greg k-h