From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751867AbdDNHwe (ORCPT ); Fri, 14 Apr 2017 03:52:34 -0400 Received: from mx1.redhat.com ([209.132.183.28]:54486 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751235AbdDNHwc (ORCPT ); Fri, 14 Apr 2017 03:52:32 -0400 DMARC-Filter: OpenDMARC Filter v1.3.2 mx1.redhat.com 243C93DBC2 Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; dmarc=none (p=none dis=none) header.from=redhat.com Authentication-Results: ext-mx06.extmail.prod.ext.phx2.redhat.com; spf=pass smtp.mailfrom=jasowang@redhat.com DKIM-Filter: OpenDKIM Filter v2.11.0 mx1.redhat.com 243C93DBC2 Subject: Re: [PATCH 1/3] ptr_ring: batch ring zeroing To: "Michael S. Tsirkin" , linux-kernel@vger.kernel.org References: <1491544049-19108-1-git-send-email-mst@redhat.com> <19f56d99-279a-5a8b-39a7-1017a3cb4bdd@redhat.com> Cc: brouer@redhat.com From: Jason Wang Message-ID: <97915bd0-ef22-4e67-1b18-3522e2369fda@redhat.com> Date: Fri, 14 Apr 2017 15:52:23 +0800 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101 Thunderbird/45.8.0 MIME-Version: 1.0 In-Reply-To: <19f56d99-279a-5a8b-39a7-1017a3cb4bdd@redhat.com> Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 8bit X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.30]); Fri, 14 Apr 2017 07:52:32 +0000 (UTC) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2017年04月12日 16:03, Jason Wang wrote: > > > On 2017年04月07日 13:49, Michael S. Tsirkin wrote: >> A known weakness in ptr_ring design is that it does not handle well the >> situation when ring is almost full: as entries are consumed they are >> immediately used again by the producer, so consumer and producer are >> writing to a shared cache line. >> >> To fix this, add batching to consume calls: as entries are >> consumed do not write NULL into the ring until we get >> a multiple (in current implementation 2x) of cache lines >> away from the producer. At that point, write them all out. >> >> We do the write out in the reverse order to keep >> producer from sharing cache with consumer for as long >> as possible. >> >> Writeout also triggers when ring wraps around - there's >> no special reason to do this but it helps keep the code >> a bit simpler. >> >> What should we do if getting away from producer by 2 cache lines >> would mean we are keeping the ring moe than half empty? >> Maybe we should reduce the batching in this case, >> current patch simply reduces the batching. >> >> Notes: >> - it is no longer true that a call to consume guarantees >> that the following call to produce will succeed. >> No users seem to assume that. >> - batching can also in theory reduce the signalling rate: >> users that would previously send interrups to the producer >> to wake it up after consuming each entry would now only >> need to do this once in a batch. >> Doing this would be easy by returning a flag to the caller. >> No users seem to do signalling on consume yet so this was not >> implemented yet. >> >> Signed-off-by: Michael S. Tsirkin >> --- >> >> Jason, I am curious whether the following gives you some of >> the performance boost that you see with vhost batching >> patches. Is vhost batching on top still helpful? > > The patch looks good to me, will have a test for vhost batching patches. > > Thanks Still helpful: before this patch: 1.84Mpps with this patch: 2.00Mpps with batch dequeuing: 2.30Mpps Acked-by: Jason Wang Thanks