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=-1.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS autolearn=ham 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 1B208C04EB9 for ; Wed, 5 Dec 2018 20:11:59 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id DA12A208E7 for ; Wed, 5 Dec 2018 20:11:58 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org DA12A208E7 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=suse.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-kernel-owner@vger.kernel.org Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728401AbeLEUL5 (ORCPT ); Wed, 5 Dec 2018 15:11:57 -0500 Received: from mx2.suse.de ([195.135.220.15]:51304 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727257AbeLEUL5 (ORCPT ); Wed, 5 Dec 2018 15:11:57 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay2.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id 22BDCADC8; Wed, 5 Dec 2018 20:11:55 +0000 (UTC) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII; format=flowed Content-Transfer-Encoding: 7bit Date: Wed, 05 Dec 2018 21:11:54 +0100 From: Roman Penyaev To: Jason Baron Cc: Alexander Viro , "Paul E. McKenney" , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org Subject: Re: [RFC PATCH 1/1] epoll: use rwlock in order to reduce ep_poll_callback() contention In-Reply-To: References: <20181203110237.14787-1-rpenyaev@suse.de> <45bce871-edfd-c402-acde-2e57e80cc522@akamai.com> <38cc83144a2ec332dead4e21214ea068@suse.de> Message-ID: <1c214a8b9e6c06589c912b55d2ef5f37@suse.de> X-Sender: rpenyaev@suse.de User-Agent: Roundcube Webmail Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 2018-12-05 17:38, Jason Baron wrote: > > I think it might be interesting for, at least testing, to see if not > grabbing > wq.lock improves your benchmarks any further? fwiw, epoll only recently > started > grabbing wq.lock bc lockdep required it. That's easy! I've just tested with the following hunk applied to my patch on top: +++ b/fs/eventpoll.c @@ -1228,7 +1228,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v break; } } - wake_up(&ep->wq); + wake_up_locked(&ep->wq); } Run time: threads w/ wq.lock w/o wq.lock ------- ---------- ----------- 8 8581ms 8602ms 16 13800ms 13715ms 32 24167ms 23817ms No big difference. According to perf the contention is on read lock and on try_to_wake_up(), the p->pi_lock, which serializes access exactly like vanished wq.lock. - 24.41% 5.39% a.out [kernel.kallsyms] [k] ep_poll_callback - 19.02% ep_poll_callback + 11.88% _raw_read_lock_irqsave + 5.74% _raw_read_unlock_irqrestore - 1.39% __wake_up_common - 1.22% try_to_wake_up + 0.98% _raw_spin_lock_irqsave -- Roman