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=-14.8 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_PATCH,MAILING_LIST_MULTI, MENTIONS_GIT_HOSTING,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED, USER_AGENT_GIT 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 533A1C3A5A6 for ; Thu, 19 Sep 2019 09:24:28 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1595C21924 for ; Thu, 19 Sep 2019 09:24:28 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=hev-cc.20150623.gappssmtp.com header.i=@hev-cc.20150623.gappssmtp.com header.b="XNpK6sD8" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388540AbfISJY1 (ORCPT ); Thu, 19 Sep 2019 05:24:27 -0400 Received: from mail-pg1-f196.google.com ([209.85.215.196]:38758 "EHLO mail-pg1-f196.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2387637AbfISJY0 (ORCPT ); Thu, 19 Sep 2019 05:24:26 -0400 Received: by mail-pg1-f196.google.com with SMTP id x10so1532913pgi.5 for ; Thu, 19 Sep 2019 02:24:26 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=hev-cc.20150623.gappssmtp.com; s=20150623; h=from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=Em5t6EauVU0sVfuGE/WQJbJCwK78aKFv2CRbjaBHg78=; b=XNpK6sD84uDyGoEet5+aP4u5D9SrABBaNu7mQmk3wqDZyY2FJAvaYouW0RJze56+/4 u2FyIWD/1woLw4N2C9dNvPlQ48PhVVf500U1a22LF2GTcNKLnJi2f3ecsGnXzAhmtyCw hvw1jwwwk5utSSiqmljGqb13mC8AVinOkPqjw4YXhTV2PmiUR9vPVOWt4OC7KIxKuxnS 0Ioe2XbUDsHJNh0VpfDD+reFOwlzlM8rGrsbcOUwdHRnzEukOcjg+DblZL53IQQQ//0T 8U7M0oYqDjIUGJ8aC9sHPNlQXvcddu+csaRHrs0PT/LqK0eOOl57h3k7aRoWIK97sbaD IXmw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20161025; h=x-gm-message-state:from:to:cc:subject:date:message-id:mime-version :content-transfer-encoding; bh=Em5t6EauVU0sVfuGE/WQJbJCwK78aKFv2CRbjaBHg78=; b=C1NzvfZB6Uk6ix0dWcrD8NjhvJBsMtYCqllt4zRU16XpJbgooZOAUgZPegF+SkMxXB 9KADggrXuVHuyY7inJAd3OhaZwXJPvEaOTWXrpaecN+K+85uuR8zNTbEXtzUDpwMoyPh PW9jiCGuCNXKw8Ao2YNoNQoYJeIy2dErQWJjOa00L2x8k1mhMi3FUq5INYBO0rQL72xb bkihTkyErflKy9O8vazfCgYTUTSOpYNdAp+yoSMYIIvPInrzRUYKNUfmx6qmzvumKKog vD129x24S090R0TgOXvecgHoxPrjXhqhSSwEtlZaTWAZb1VctL8pKz5dT0cvtEzf99hQ UVEQ== X-Gm-Message-State: APjAAAWxFCHrmk/785DIlqwMeeNfdKXQs6yt3XSyYhGVsvR5VOxzJzUS 6jL0c27pQwwzv6otmjzdjpxDcQ== X-Google-Smtp-Source: APXvYqz6XDwzdrsaDrWccJyY0LG2FMNErzKhxv4IReDifWCzG2NutSEjvt/JjZpO9qyPwtZgk259PA== X-Received: by 2002:a62:7c4d:: with SMTP id x74mr9086260pfc.95.1568885066049; Thu, 19 Sep 2019 02:24:26 -0700 (PDT) Received: from hev-sbc.hz.ali.com ([47.89.83.40]) by smtp.gmail.com with ESMTPSA id s19sm9749108pfe.86.2019.09.19.02.24.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Thu, 19 Sep 2019 02:24:24 -0700 (PDT) From: hev To: linux-fsdevel@vger.kernel.org Cc: Heiher , Al Viro , Andrew Morton , Davide Libenzi , Davidlohr Bueso , Dominik Brodowski , Eric Wong , Jason Baron , Linus Torvalds , Roman Penyaev , Sridhar Samudrala , linux-kernel@vger.kernel.org Subject: [PATCH RESEND v2] fs/epoll: Remove unnecessary wakeups of nested epoll that in ET mode Date: Thu, 19 Sep 2019 17:24:13 +0800 Message-Id: <20190919092413.11141-1-r@hev.cc> X-Mailer: git-send-email 2.23.0 MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Heiher Take the case where we have: t0 | (ew) e0 | (et) e1 | (lt) s0 t0: thread 0 e0: epoll fd 0 e1: epoll fd 1 s0: socket fd 0 ew: epoll_wait et: edge-trigger lt: level-trigger When s0 fires an event, e1 catches the event, and then e0 catches an event from e1. After this, There is a thread t0 do epoll_wait() many times on e0, it should only get one event in total, because e1 is a dded to e0 in edge-triggered mode. This patch only allows the wakeup(&ep->poll_wait) in ep_scan_ready_list under two conditions: 1. depth == 0. 2. There have event is added to ep->ovflist during processing. Test code: #include #include #include int main(int argc, char *argv[]) { int sfd[2]; int efd[2]; struct epoll_event e; if (socketpair(AF_UNIX, SOCK_STREAM, 0, sfd) < 0) goto out; efd[0] = epoll_create(1); if (efd[0] < 0) goto out; efd[1] = epoll_create(1); if (efd[1] < 0) goto out; e.events = EPOLLIN; if (epoll_ctl(efd[1], EPOLL_CTL_ADD, sfd[0], &e) < 0) goto out; e.events = EPOLLIN | EPOLLET; if (epoll_ctl(efd[0], EPOLL_CTL_ADD, efd[1], &e) < 0) goto out; if (write(sfd[1], "w", 1) != 1) goto out; if (epoll_wait(efd[0], &e, 1, 0) != 1) goto out; if (epoll_wait(efd[0], &e, 1, 0) != 0) goto out; close(efd[0]); close(efd[1]); close(sfd[0]); close(sfd[1]); return 0; out: return -1; } More tests: https://github.com/heiher/epoll-wakeup Cc: Al Viro Cc: Andrew Morton Cc: Davide Libenzi Cc: Davidlohr Bueso Cc: Dominik Brodowski Cc: Eric Wong Cc: Jason Baron Cc: Linus Torvalds Cc: Roman Penyaev Cc: Sridhar Samudrala Cc: linux-kernel@vger.kernel.org Cc: linux-fsdevel@vger.kernel.org Signed-off-by: hev --- fs/eventpoll.c | 5 ++++- 1 file changed, 4 insertions(+), 1 deletion(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index c4159bcc05d9..fa71468dbd51 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -685,6 +685,9 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep, if (!ep_locked) mutex_lock_nested(&ep->mtx, depth); + if (!depth || list_empty_careful(&ep->rdllist)) + pwake++; + /* * Steal the ready list, and re-init the original one to the * empty list. Also, set ep->ovflist to NULL so that events @@ -755,7 +758,7 @@ static __poll_t ep_scan_ready_list(struct eventpoll *ep, mutex_unlock(&ep->mtx); /* We have to call this outside the lock */ - if (pwake) + if (pwake == 2) ep_poll_safewake(&ep->poll_wait); return res; -- 2.23.0