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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1E8C0C7EE43 for ; Fri, 9 Jun 2023 13:50:04 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231266AbjFINuC (ORCPT ); Fri, 9 Jun 2023 09:50:02 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:57522 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238987AbjFINtu (ORCPT ); Fri, 9 Jun 2023 09:49:50 -0400 Received: from out30-99.freemail.mail.aliyun.com (out30-99.freemail.mail.aliyun.com [115.124.30.99]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7C86018D; Fri, 9 Jun 2023 06:49:47 -0700 (PDT) X-Alimail-AntiSpam: AC=PASS;BC=-1|-1;BR=01201311R131e4;CH=green;DM=||false|;DS=||;FP=0|-1|-1|-1|0|-1|-1|-1;HT=ay29a033018045168;MF=xianting.tian@linux.alibaba.com;NM=1;PH=DS;RN=17;SR=0;TI=SMTPD_---0VkiId6T_1686318579; Received: from 30.236.10.144(mailfrom:xianting.tian@linux.alibaba.com fp:SMTPD_---0VkiId6T_1686318579) by smtp.aliyun-inc.com; Fri, 09 Jun 2023 21:49:41 +0800 Message-ID: <91aa6ce0-e8a3-21ac-d29e-b2a47f6386d1@linux.alibaba.com> Date: Fri, 9 Jun 2023 21:49:39 +0800 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.15; rv:102.0) Gecko/20100101 Thunderbird/102.10.0 Subject: Re: [PATCH 1/3] virtio-crypto: fixup potential cpu stall when free unused bufs To: Greg KH Cc: arei.gonglei@huawei.com, mst@redhat.com, jasowang@redhat.com, xuanzhuo@linux.alibaba.com, herbert@gondor.apana.org.au, davem@davemloft.net, amit@kernel.org, arnd@arndb.de, marcel@holtmann.org, johan.hedberg@gmail.com, luiz.dentz@gmail.com, linux-bluetooth@vger.kernel.org, virtualization@lists.linux-foundation.org, linux-crypto@vger.kernel.org, linux-kernel@vger.kernel.org, Xianting Tian References: <20230609131817.712867-1-xianting.tian@linux.alibaba.com> <20230609131817.712867-2-xianting.tian@linux.alibaba.com> <2023060924-skinning-reset-e256@gregkh> <2023060940-wrongdoer-wince-5701@gregkh> From: Xianting Tian In-Reply-To: <2023060940-wrongdoer-wince-5701@gregkh> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org 在 2023/6/9 下午9:41, Greg KH 写道: > On Fri, Jun 09, 2023 at 03:39:24PM +0200, Greg KH wrote: >> On Fri, Jun 09, 2023 at 09:18:15PM +0800, Xianting Tian wrote: >>> From: Xianting Tian >>> >>> Cpu stall issue may happen if device is configured with multi queues >>> and large queue depth, so fix it. >>> >>> Signed-off-by: Xianting Tian >>> --- >>> drivers/crypto/virtio/virtio_crypto_core.c | 1 + >>> 1 file changed, 1 insertion(+) >>> >>> diff --git a/drivers/crypto/virtio/virtio_crypto_core.c b/drivers/crypto/virtio/virtio_crypto_core.c >>> index 1198bd306365..94849fa3bd74 100644 >>> --- a/drivers/crypto/virtio/virtio_crypto_core.c >>> +++ b/drivers/crypto/virtio/virtio_crypto_core.c >>> @@ -480,6 +480,7 @@ static void virtcrypto_free_unused_reqs(struct virtio_crypto *vcrypto) >>> kfree(vc_req->req_data); >>> kfree(vc_req->sgs); >>> } >>> + cond_resched(); >> that's not "fixing a stall", it is "call the scheduler because we are >> taking too long". The CPU isn't stalled at all, just busy. >> >> Are you sure this isn't just a bug in the code? Why is this code taking >> so long that you have to force the scheduler to run? This is almost >> always a sign that something else needs to be fixed instead. > And same comment on the other 2 patches, please fix this properly. > > Also, this is a tight loop that is just freeing memory, why is it taking > so long? Why do you want it to take longer (which is what you are doing > here), ideally it would be faster, not slower, so you are now slowing > down the system overall with this patchset, right? yes, it is the similar fix with one for virtio-net https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/commit/drivers/net/virtio_net.c?h=v6.4-rc5&id=f8bb5104394560e29017c25bcade4c6b7aabd108 > > thanks, > > greg k-h