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=-9.1 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY, SPF_PASS,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 4F393C282CD for ; Mon, 28 Jan 2019 16:11:54 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1E9202177E for ; Mon, 28 Jan 2019 16:11:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548691914; bh=3s81iF9vciymf2w4xPReymvYVpe3eQAc3UABl2EwJ94=; h=From:To:Cc:Subject:Date:In-Reply-To:References:List-ID:From; b=oIdf778ny+nk7QRfxk+9WNV6uCQTBCRYOpBy0XWsVgJrgNggtnZIqw+9lTyCY2ep2 uPvjacwfubdYTkrjeWC5JcTeP6ytWag+7J8y/XHGPSQIJVRlHHYx8gP5z8R8VSYKfP kn/l1DOos6qKteOS/gKB00CwEitesBx4qCMuGU+M= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1733047AbfA1QLw (ORCPT ); Mon, 28 Jan 2019 11:11:52 -0500 Received: from mail.kernel.org ([198.145.29.99]:39266 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1733026AbfA1QLu (ORCPT ); Mon, 28 Jan 2019 11:11:50 -0500 Received: from sasha-vm.mshome.net (c-73-47-72-35.hsd1.nh.comcast.net [73.47.72.35]) (using TLSv1.2 with cipher ECDHE-RSA-AES128-GCM-SHA256 (128/128 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id 3AF7121848; Mon, 28 Jan 2019 16:11:47 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1548691909; bh=3s81iF9vciymf2w4xPReymvYVpe3eQAc3UABl2EwJ94=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=ukdxcYSEVB7Gmo/vdEdCwwmSKUTyxNy0Xp5IvuhikUJ4e+BMeHfYoDVYT/tZHPxmZ MoxCB1PVjKOjCsC+zJBJkAD4VL40oZmYADJEO7i+MJDwXVly3FhZ5X9GnZPtme917+ tUjbtxXvVxGWFm/+ZRDF55vGZfHJTsZa95drMFRc= From: Sasha Levin To: linux-kernel@vger.kernel.org, stable@vger.kernel.org Cc: Davidlohr Bueso , Davidlohr Bueso , Al Viro , Jason Baron , Andrew Morton , Linus Torvalds , Sasha Levin , linux-fsdevel@vger.kernel.org Subject: [PATCH AUTOSEL 4.19 255/258] fs/epoll: drop ovflist branch prediction Date: Mon, 28 Jan 2019 10:59:21 -0500 Message-Id: <20190128155924.51521-255-sashal@kernel.org> X-Mailer: git-send-email 2.19.1 In-Reply-To: <20190128155924.51521-1-sashal@kernel.org> References: <20190128155924.51521-1-sashal@kernel.org> MIME-Version: 1.0 X-Patchwork-Hint: Ignore Content-Transfer-Encoding: 8bit Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org From: Davidlohr Bueso [ Upstream commit 76699a67f3041ff4c7af6d6ee9be2bfbf1ffb671 ] The ep->ovflist is a secondary ready-list to temporarily store events that might occur when doing sproc without holding the ep->wq.lock. This accounts for every time we check for ready events and also send events back to userspace; both callbacks, particularly the latter because of copy_to_user, can account for a non-trivial time. As such, the unlikely() check to see if the pointer is being used, seems both misleading and sub-optimal. In fact, we go to an awful lot of trouble to sync both lists, and populating the ovflist is far from an uncommon scenario. For example, profiling a concurrent epoll_wait(2) benchmark, with CONFIG_PROFILE_ANNOTATED_BRANCHES shows that for a two threads a 33% incorrect rate was seen; and when incrementally increasing the number of epoll instances (which is used, for example for multiple queuing load balancing models), up to a 90% incorrect rate was seen. Similarly, by deleting the prediction, 3% throughput boost was seen across incremental threads. Link: http://lkml.kernel.org/r/20181108051006.18751-4-dave@stgolabs.net Signed-off-by: Davidlohr Bueso Reviewed-by: Andrew Morton Cc: Al Viro Cc: Jason Baron Signed-off-by: Andrew Morton Signed-off-by: Linus Torvalds Signed-off-by: Sasha Levin --- fs/eventpoll.c | 2 +- 1 file changed, 1 insertion(+), 1 deletion(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 42bbe6824b4b..58f48ea0db23 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -1154,7 +1154,7 @@ static int ep_poll_callback(wait_queue_entry_t *wait, unsigned mode, int sync, v * semantics). All the events that happen during that period of time are * chained in ep->ovflist and requeued later on. */ - if (unlikely(ep->ovflist != EP_UNACTIVE_PTR)) { + if (ep->ovflist != EP_UNACTIVE_PTR) { if (epi->next == EP_UNACTIVE_PTR) { epi->next = ep->ovflist; ep->ovflist = epi; -- 2.19.1