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 9D5D2EB64DC for ; Fri, 21 Jul 2023 14:59:07 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S231502AbjGUO7G (ORCPT ); Fri, 21 Jul 2023 10:59:06 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:39616 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229973AbjGUO7D (ORCPT ); Fri, 21 Jul 2023 10:59:03 -0400 Received: from us-smtp-delivery-124.mimecast.com (us-smtp-delivery-124.mimecast.com [170.10.133.124]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 65AF619B6 for ; Fri, 21 Jul 2023 07:58:14 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=redhat.com; s=mimecast20190719; t=1689951493; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: in-reply-to:in-reply-to:references:references; bh=U1qQ37MMJd6MivrcwkUnYSPTqHJ5IN0DRXHoCePfwTc=; b=HFbHWdvf9VCJXOsnBb3h5lmnGUvmFrM0+10r8yOhnGrv2m5qCOkxBcwMjykwFcMVTWFefO CAsj8mNQUVNw+39Ef9B8knQJSOoQWhS8ZE7XzLURYpjUcoh7iP9/MRCSovnkRkoBDVQB8/ 6CUeme7UmSLDubDoD/6AheX4YRn0V98= Received: from mimecast-mx02.redhat.com (mimecast-mx02.redhat.com [66.187.233.88]) by relay.mimecast.com with ESMTP with STARTTLS (version=TLSv1.2, cipher=TLS_ECDHE_RSA_WITH_AES_256_GCM_SHA384) id us-mta-80--sJhcl7SMfaUKSuhATyG2A-1; Fri, 21 Jul 2023 10:58:10 -0400 X-MC-Unique: -sJhcl7SMfaUKSuhATyG2A-1 Received: from smtp.corp.redhat.com (int-mx02.intmail.prod.int.rdu2.redhat.com [10.11.54.2]) (using TLSv1.2 with cipher AECDH-AES256-SHA (256/256 bits)) (No client certificate requested) by mimecast-mx02.redhat.com (Postfix) with ESMTPS id CE9A2800B35; Fri, 21 Jul 2023 14:58:09 +0000 (UTC) Received: from [10.39.208.41] (unknown [10.39.208.41]) by smtp.corp.redhat.com (Postfix) with ESMTPS id B43304094DC0; Fri, 21 Jul 2023 14:58:07 +0000 (UTC) Message-ID: <6278a4aa-8901-b0e3-342f-5753a4bf32af@redhat.com> Date: Fri, 21 Jul 2023 16:58:04 +0200 MIME-Version: 1.0 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:102.0) Gecko/20100101 Thunderbird/102.13.0 Subject: Re: [PATCH net-next v4 2/2] virtio-net: add cond_resched() to the command waiting loop Content-Language: en-US To: "Michael S. Tsirkin" Cc: Shannon Nelson , Jason Wang , xuanzhuo@linux.alibaba.com, netdev@vger.kernel.org, linux-kernel@vger.kernel.org, virtualization@lists.linux-foundation.org, edumazet@google.com, kuba@kernel.org, pabeni@redhat.com, davem@davemloft.net References: <20230720083839.481487-1-jasowang@redhat.com> <20230720083839.481487-3-jasowang@redhat.com> <20230720170001-mutt-send-email-mst@kernel.org> <263a5ad7-1189-3be3-70de-c38a685bebe0@redhat.com> <20230721104445-mutt-send-email-mst@kernel.org> From: Maxime Coquelin In-Reply-To: <20230721104445-mutt-send-email-mst@kernel.org> Content-Type: text/plain; charset=UTF-8; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 3.1 on 10.11.54.2 Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 7/21/23 16:45, Michael S. Tsirkin wrote: > On Fri, Jul 21, 2023 at 04:37:00PM +0200, Maxime Coquelin wrote: >> >> >> On 7/20/23 23:02, Michael S. Tsirkin wrote: >>> On Thu, Jul 20, 2023 at 01:26:20PM -0700, Shannon Nelson wrote: >>>> On 7/20/23 1:38 AM, Jason Wang wrote: >>>>> >>>>> Adding cond_resched() to the command waiting loop for a better >>>>> co-operation with the scheduler. This allows to give CPU a breath to >>>>> run other task(workqueue) instead of busy looping when preemption is >>>>> not allowed on a device whose CVQ might be slow. >>>>> >>>>> Signed-off-by: Jason Wang >>>> >>>> This still leaves hung processes, but at least it doesn't pin the CPU any >>>> more. Thanks. >>>> Reviewed-by: Shannon Nelson >>>> >>> >>> I'd like to see a full solution >>> 1- block until interrupt >> >> Would it make sense to also have a timeout? >> And when timeout expires, set FAILED bit in device status? > > virtio spec does not set any limits on the timing of vq > processing. Indeed, but I thought the driver could decide it is too long for it. The issue is we keep waiting with rtnl locked, it can quickly make the system unusable. >>> 2- still handle surprise removal correctly by waking in that case >>> >>> >>> >>>>> --- >>>>> drivers/net/virtio_net.c | 4 +++- >>>>> 1 file changed, 3 insertions(+), 1 deletion(-) >>>>> >>>>> diff --git a/drivers/net/virtio_net.c b/drivers/net/virtio_net.c >>>>> index 9f3b1d6ac33d..e7533f29b219 100644 >>>>> --- a/drivers/net/virtio_net.c >>>>> +++ b/drivers/net/virtio_net.c >>>>> @@ -2314,8 +2314,10 @@ static bool virtnet_send_command(struct virtnet_info *vi, u8 class, u8 cmd, >>>>> * into the hypervisor, so the request should be handled immediately. >>>>> */ >>>>> while (!virtqueue_get_buf(vi->cvq, &tmp) && >>>>> - !virtqueue_is_broken(vi->cvq)) >>>>> + !virtqueue_is_broken(vi->cvq)) { >>>>> + cond_resched(); >>>>> cpu_relax(); >>>>> + } >>>>> >>>>> return vi->ctrl->status == VIRTIO_NET_OK; >>>>> } >>>>> -- >>>>> 2.39.3 >>>>> >>>>> _______________________________________________ >>>>> Virtualization mailing list >>>>> Virtualization@lists.linux-foundation.org >>>>> https://lists.linuxfoundation.org/mailman/listinfo/virtualization >>> >