From patchwork Wed Nov 14 18:25:32 2018 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Davidlohr Bueso X-Patchwork-Id: 10682997 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7D7A4139B for ; Wed, 14 Nov 2018 18:25:55 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 6F5322BE87 for ; Wed, 14 Nov 2018 18:25:55 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id 634D22BE8B; Wed, 14 Nov 2018 18:25:55 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-7.9 required=2.0 tests=BAYES_00,MAILING_LIST_MULTI, RCVD_IN_DNSWL_HI autolearn=ham version=3.3.1 Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id 0EDC02BE87 for ; Wed, 14 Nov 2018 18:25:55 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728686AbeKOEaL (ORCPT ); Wed, 14 Nov 2018 23:30:11 -0500 Received: from smtp2.provo.novell.com ([137.65.250.81]:59757 "EHLO smtp2.provo.novell.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1727576AbeKOEaL (ORCPT ); Wed, 14 Nov 2018 23:30:11 -0500 Received: from localhost.localdomain (prv-ext-foundry1int.gns.novell.com [137.65.251.240]) by smtp2.provo.novell.com with ESMTP (TLS encrypted); Wed, 14 Nov 2018 11:25:43 -0700 From: Davidlohr Bueso To: akpm@linux-foundation.org Cc: jbaron@akamai.com, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org, linux-kernel@vger.kernel.org, dave@stgolabs.net, Davidlohr Bueso Subject: [PATCH 2/2] fs/epoll: deal with wait_queue only once Date: Wed, 14 Nov 2018 10:25:32 -0800 Message-Id: <20181114182532.27981-2-dave@stgolabs.net> X-Mailer: git-send-email 2.16.4 In-Reply-To: <20181114182532.27981-1-dave@stgolabs.net> References: <20181114182532.27981-1-dave@stgolabs.net> Sender: linux-fsdevel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org X-Virus-Scanned: ClamAV using ClamSMTP There is no reason why we rearm the waitiqueue upon every fetch_events retry (for when events are found yet send_events() fails). If nothing else, this saves four lock operations per retry, and furthermore reduces the scope of the lock even further. Signed-off-by: Davidlohr Bueso --- fs/eventpoll.c | 24 ++++++++++++++++-------- 1 file changed, 16 insertions(+), 8 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 7e2b5f3d6b3e..25b0c94cc091 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1749,6 +1749,7 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, { int res = 0, eavail, timed_out = 0; u64 slack = 0; + bool waiter = false; wait_queue_entry_t wait; ktime_t expires, *to = NULL; @@ -1786,6 +1787,15 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, if (eavail) goto send_events; + if (!waiter) { + waiter = true; + init_waitqueue_entry(&wait, current); + + spin_lock_irq(&ep->wq.lock); + __add_wait_queue_exclusive(&ep->wq, &wait); + spin_unlock_irq(&ep->wq.lock); + } + /* * Busy poll timed out. Drop NAPI ID for now, we can add * it back in when we have moved a socket with a valid NAPI @@ -1798,10 +1808,6 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, * We need to sleep here, and we will be wake up by * ep_poll_callback() when events will become available. */ - init_waitqueue_entry(&wait, current); - spin_lock_irq(&ep->wq.lock); - __add_wait_queue_exclusive(&ep->wq, &wait); - spin_unlock_irq(&ep->wq.lock); for (;;) { /* @@ -1836,10 +1842,6 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, __set_current_state(TASK_RUNNING); - spin_lock_irq(&ep->wq.lock); - __remove_wait_queue(&ep->wq, &wait); - spin_unlock_irq(&ep->wq.lock); - send_events: /* * Try to transfer events to user space. In case we get 0 events and @@ -1850,6 +1852,12 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, !(res = ep_send_events(ep, events, maxevents)) && !timed_out) goto fetch_events; + if (waiter) { + spin_lock_irq(&ep->wq.lock); + __remove_wait_queue(&ep->wq, &wait); + spin_unlock_irq(&ep->wq.lock); + } + return res; }