From patchwork Fri Nov 6 23:16:32 2020 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Soheil Hassas Yeganeh X-Patchwork-Id: 11888361 Return-Path: Received: from mail.kernel.org (pdx-korg-mail-1.web.codeaurora.org [172.30.200.123]) by pdx-korg-patchwork-2.web.codeaurora.org (Postfix) with ESMTP id 7D0C714B4 for ; Fri, 6 Nov 2020 23:18:16 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 584E0206A5 for ; Fri, 6 Nov 2020 23:18:16 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=gmail.com header.i=@gmail.com header.b="JgqfE4j2" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1728818AbgKFXSK (ORCPT ); Fri, 6 Nov 2020 18:18:10 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42418 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1728245AbgKFXRy (ORCPT ); Fri, 6 Nov 2020 18:17:54 -0500 Received: from mail-qt1-x843.google.com (mail-qt1-x843.google.com [IPv6:2607:f8b0:4864:20::843]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 51AD1C0613D6; Fri, 6 Nov 2020 15:17:52 -0800 (PST) Received: by mail-qt1-x843.google.com with SMTP id j31so2005413qtb.8; Fri, 06 Nov 2020 15:17:52 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20161025; h=from:to:cc:subject:date:message-id:in-reply-to:references :mime-version:content-transfer-encoding; bh=nOSFREc0POUXsBcyqAN5If5e3Op5s8v2XbVHIhjOP4Y=; b=JgqfE4j2JpxJLmj0zMJ1yzwbdykmApIOch3Xx3jw4p1oJ8+MyRvrmm4GuDvkqsO7lt 7VmVyRlv8D/K/cIE1E4+sU3RTK3pYrLv7dc9IKSine5WpCXlLLVQL6LXxRSyFGk9kQxP SqfXzNUUuYJlPcF5qHqiUv48rq5vE2xph+EJN721IEfZj3jyYdiw3LX1qHu7z3FyaMAP FMcll8IZnZiIbYnj3nedzbXPY8K79d8nfWwntOgG9yFOTl1lejMS2B6uOSvaksCCUR/c cURrpjB8Pps0U3WCwAcB7BoVbU/qND6Qy6PL5fNrMpNRlGtPGfzSGBjRaHzb1TlK331b NPLg== 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:in-reply-to :references:mime-version:content-transfer-encoding; bh=nOSFREc0POUXsBcyqAN5If5e3Op5s8v2XbVHIhjOP4Y=; b=J+gRGpghva7rHW2iGZY5M+wnL1EkujbG+073yHLLvBkpRi1D60OCZcRd66pQdt6LqG xi5bKPLlKnf6S7n5tjk3p0ikqkeTMhaIjui7Rm3vDU1XqrMxxEE/tGuqGHgoG/DfQdAx KVDBSMeoZFzgr7uyKX0q90TPz4g9x3iUf38co2tTCY22NFzTGj/2pDAOpH/cU7SW7MnP 6vmvBnzmzm450/vv1A9kdNsYazzRMp+ulzGM5eZsf4P0wW6WGTMeUbgxR+nGDLPBRUyu dlU/4CLcTOWWyqLvakgSxEFP0BcfoOeptjTJvsJfjQHgucBmEhVMRnMntMn/fEhrdnxV PnVQ== X-Gm-Message-State: AOAM532V+o0U3pjtoAvZqThj88onuWOqprk1U4tfwyp9VlWYVGEu1BSY RZ7mPdnHvQJNhvvS6HpScN0= X-Google-Smtp-Source: ABdhPJzxGx8FL5Mjc33i9OrWQxJ0rNlUEGUzIEfMSVyZooARvf49FSMcVCJsrDzETAN5A7A+JM4oYg== X-Received: by 2002:aed:31c5:: with SMTP id 63mr3768102qth.84.1604704671575; Fri, 06 Nov 2020 15:17:51 -0800 (PST) Received: from soheil4.nyc.corp.google.com ([2620:0:1003:312:a6ae:11ff:fe18:6946]) by smtp.gmail.com with ESMTPSA id p136sm1519357qke.25.2020.11.06.15.17.51 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Fri, 06 Nov 2020 15:17:51 -0800 (PST) From: Soheil Hassas Yeganeh To: torvalds@linux-foundation.org, viro@zeniv.linux.org.uk, linux-fsdevel@vger.kernel.org Cc: linux-kernel@vger.kernel.org, akpm@linux-foundation.org, dave@stgolabs.net, edumazet@google.com, willemb@google.com, khazhy@google.com, guantaol@google.com, Soheil Hassas Yeganeh Subject: [PATCH 5/8] epoll: simplify and optimize busy loop logic Date: Fri, 6 Nov 2020 18:16:32 -0500 Message-Id: <20201106231635.3528496-6-soheil.kdev@gmail.com> X-Mailer: git-send-email 2.29.1.341.ge80a0c044ae-goog In-Reply-To: <20201106231635.3528496-1-soheil.kdev@gmail.com> References: <20201106231635.3528496-1-soheil.kdev@gmail.com> MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-fsdevel@vger.kernel.org From: Soheil Hassas Yeganeh ep_events_available() is called multiple times around the busy loop logic, even though the logic is generally not used. ep_reset_busy_poll_napi_id() is similarly always called, even when busy loop is not used. Eliminate ep_reset_busy_poll_napi_id() and inline it inside ep_busy_loop(). Make ep_busy_loop() return whether there are any events available after the busy loop. This will eliminate unnecessary loads and branches, and simplifies the loop. Signed-off-by: Soheil Hassas Yeganeh Reviewed-by: Eric Dumazet Reviewed-by: Willem de Bruijn Reviewed-by: Khazhismel Kumykov --- fs/eventpoll.c | 42 +++++++++++++++++++----------------------- 1 file changed, 19 insertions(+), 23 deletions(-) diff --git a/fs/eventpoll.c b/fs/eventpoll.c index 5226b0cb1098..28c1d341d2e6 100644 --- a/fs/eventpoll.c +++ b/fs/eventpoll.c @@ -391,19 +391,26 @@ static bool ep_busy_loop_end(void *p, unsigned long start_time) * busy loop will return if need_resched or ep_events_available. * * we must do our busy polling with irqs enabled + * + * Returns whether new events are available after a successful busy loop. */ -static void ep_busy_loop(struct eventpoll *ep, int nonblock) +static bool ep_busy_loop(struct eventpoll *ep, int nonblock) { unsigned int napi_id = READ_ONCE(ep->napi_id); - if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on()) + if ((napi_id >= MIN_NAPI_ID) && net_busy_loop_on()) { napi_busy_loop(napi_id, nonblock ? NULL : ep_busy_loop_end, ep); -} - -static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep) -{ - if (ep->napi_id) + if (ep_events_available(ep)) + return true; + /* + * 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 + * ID onto the ready list. + */ ep->napi_id = 0; + return false; + } + return false; } /* @@ -444,12 +451,9 @@ static inline void ep_set_busy_poll_napi_id(struct epitem *epi) #else -static inline void ep_busy_loop(struct eventpoll *ep, int nonblock) -{ -} - -static inline void ep_reset_busy_poll_napi_id(struct eventpoll *ep) +static inline bool ep_busy_loop(struct eventpoll *ep, int nonblock) { + return false; } static inline void ep_set_busy_poll_napi_id(struct epitem *epi) @@ -1857,21 +1861,13 @@ static int ep_poll(struct eventpoll *ep, struct epoll_event __user *events, } fetch_events: - - if (!ep_events_available(ep)) - ep_busy_loop(ep, timed_out); - eavail = ep_events_available(ep); + if (!eavail) + eavail = ep_busy_loop(ep, timed_out); + if (eavail) goto send_events; - /* - * 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 - * ID onto the ready list. - */ - ep_reset_busy_poll_napi_id(ep); - do { if (signal_pending(current)) return -EINTR;