From: Klaus Jensen <its@irrelevant.dk>
To: Alan Adamson <alan.adamson@oracle.com>
Cc: qemu-devel@nongnu.org, kbusch@kernel.org, qemu-block@nongnu.org
Subject: Re: [RFC 0/1] hw/nvme: add atomic write support
Date: Wed, 8 May 2024 12:17:08 +0200 [thread overview]
Message-ID: <ZjtRJP7roXOdR236@cormorant.local> (raw)
In-Reply-To: <20240415234639.3021291-1-alan.adamson@oracle.com>
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On Apr 15 16:46, Alan Adamson wrote:
> Since there is discussion in the Linux NVMe Driver community to add NVMe Atomic Write
> support, it would be desirable to test it with qemu nvme emulation.
>
> Initially, this RFC will focus on supporting NVMe controller atomic write parameters(AWUN,
> AWUPF, and ACWU) but will be extended to support Namespace parameters (NAWUN, NAWUPF
> and NACWU).
>
> Atomic Write Parameters for NVMe QEMU
> -------------------------------------
> New NVMe QEMU Parameters (See NVMe Specification for details):
> atomic.dn (default off) - Set the value of Disable Normal.
> atomic.awun=UINT16 (default: 0)
> atomic.awupf=UINT16 (default: 0)
> atomic.acwu=UINT16 (default: 0)
>
> qemu command line example:
> qemu-system-x86_64 -cpu host --enable-kvm -smp cpus=4 -no-reboot -m 8192M -drive file=./disk.img,if=ide \
> -boot c -device e1000,netdev=net0,mac=DE:CC:CC:EF:99:88 -netdev tap,id=net0 \
> -device nvme,id=nvme-ctrl-0,serial=nvme-1,atomic.dn=off,atomic.awun=63,atomic.awupf=63,atomic.acwu=0 \
> -drive file=./nvme.img,if=none,id=nvm-1 -device nvme-ns,drive=nvm-1,bus=nvme-ctrl-0 nvme-ns,drive=nvm-1,bus=nvme-ctrl-0
>
> Making Writes Atomic:
> ---------------------
> - Prior to a command being pulled off the SQ and executed, a check is made to see if it
> conflicts "atomically" with a currently executing command.
> - All currently executing commands on the same namespace, across all SQs need to be checked.
> - If an atomic conflict is detected, the command is not started and remains on the queue.
>
> Testing
> -------
> NVMe QEMU Parameters used: atomic.dn=off,atomic.awun=63,atomic.awupf=63,atomic.acwu=0
>
> # nvme id-ctrl /dev/nvme0 | grep awun
> awun : 63
> # nvme id-ctrl /dev/nvme0 | grep awupf
> awupf : 63
> # nvme id-ctrl /dev/nvme0 | grep acwu
> acwu : 0 < Since qemu-nvme doesn't support Compare and Write, this is always zero
> # nvme get-feature /dev/nvme0 -f 0xa
> get-feature:0x0a (Write Atomicity Normal), Current value:00000000
> #
>
> # fio --filename=/dev/nvme0n1 --direct=1 --rw=randwrite --bs=32k --iodepth=256 --name=iops --numjobs=50 --verify=crc64 --verify_fatal=1 --ioengine=libaio
>
> When executed without atomic write support, eventually the following error will be
> observed:
>
> crc64: verify failed at file /dev/nvme0n1 offset 857669632, length 32768
> (requested block: offset=857669632, length=32768, flags=88)
> Expected CRC: 9c87d3539dafdca0
> Received CRC: d521f7ea3b69d2ee
>
> When executed with atomic write support, this error no longer happens.
>
> Questions
> ---------
> AWUN vs AWUPF - Does the nvme emulation need to do treat these differently? Currently the
> larger of the two will be used as the max atomic write size.
>
> Future Work
> -----------
> - Namespace support (NAWUN, NAWUPF and NACWU)
> - Namespace Boundary support (NABSN, NABO, and NABSPF)
> - Atomic Compare and Write Unit (ACWU)
>
> Alan Adamson (1):
> nvme: add atomic write support
>
> hw/nvme/ctrl.c | 147 ++++++++++++++++++++++++++++++++++++++++++++++++-
> hw/nvme/nvme.h | 17 ++++++
> 2 files changed, 163 insertions(+), 1 deletion(-)
>
> --
> 2.39.3
>
Hi Alan,
I have no obvious qualms about this. It is clearly useful for driver
testing and verification and does not negatively impact the performance
when this "faked" feature is not enabled.
Acked-by: Klaus Jensen <k.jensen@samsung.com>
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prev parent reply other threads:[~2024-05-08 10:18 UTC|newest]
Thread overview: 3+ messages / expand[flat|nested] mbox.gz Atom feed top
2024-04-15 23:46 [RFC 0/1] hw/nvme: add atomic write support Alan Adamson
2024-04-15 23:46 ` [RFC 1/1] " Alan Adamson
2024-05-08 10:17 ` Klaus Jensen [this message]
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