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=-3.0 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, MAILING_LIST_MULTI,SPF_PASS,USER_AGENT_NEOMUTT 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 6BA43C04EB8 for ; Thu, 6 Dec 2018 04:04:40 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 16D7F214C1 for ; Thu, 6 Dec 2018 04:04:39 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org 16D7F214C1 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=stgolabs.net 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 S1728929AbeLFEEi (ORCPT ); Wed, 5 Dec 2018 23:04:38 -0500 Received: from mx2.suse.de ([195.135.220.15]:41818 "EHLO mx1.suse.de" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1727695AbeLFEEi (ORCPT ); Wed, 5 Dec 2018 23:04:38 -0500 X-Virus-Scanned: by amavisd-new at test-mx.suse.de Received: from relay1.suse.de (unknown [195.135.220.254]) by mx1.suse.de (Postfix) with ESMTP id B8F60AE7A; Thu, 6 Dec 2018 04:04:36 +0000 (UTC) Date: Wed, 5 Dec 2018 20:04:30 -0800 From: Davidlohr Bueso To: Jason Baron Cc: Roman Penyaev , Alexander Viro , "Paul E. McKenney" , Linus Torvalds , linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, akpm@linux-foundation.org Subject: Re: [RFC PATCH 1/1] epoll: use rwlock in order to reduce ep_poll_callback() contention Message-ID: <20181206040430.d7wjik6lt7kr75m6@linux-r8p5> References: <20181203110237.14787-1-rpenyaev@suse.de> <45bce871-edfd-c402-acde-2e57e80cc522@akamai.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii; format=flowed Content-Disposition: inline In-Reply-To: <45bce871-edfd-c402-acde-2e57e80cc522@akamai.com> User-Agent: NeoMutt/20180323 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 12/3/18 6:02 AM, Roman Penyaev wrote: > The main change is in replacement of the spinlock with a rwlock, which is > taken on read in ep_poll_callback(), and then by adding poll items to the > tail of the list using xchg atomic instruction. Write lock is taken > everywhere else in order to stop list modifications and guarantee that list > updates are fully completed (I assume that write side of a rwlock does not > starve, it seems qrwlock implementation has these guarantees). Its good then that Will recently ported qrwlocks to arm64, which iirc had a bad case of writer starvation. In general, qrwlock will maintain reader to writer ratios of acquisitions fairly well, but will favor readers over writers in scenarios where when too many tasks (more than ncpus). Thanks, Davidlohr