From patchwork Tue Mar 9 08:42:08 2021 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Thomas Gleixner X-Patchwork-Id: 12124423 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=-15.8 required=3.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,INCLUDES_CR_TRAILER, INCLUDES_PATCH,MAILING_LIST_MULTI,SPF_HELO_NONE,SPF_PASS autolearn=unavailable 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 D1593C433E0 for ; Tue, 9 Mar 2021 08:46:39 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 892D165266 for ; Tue, 9 Mar 2021 08:46:39 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S229681AbhCIIqH (ORCPT ); Tue, 9 Mar 2021 03:46:07 -0500 Received: from Galois.linutronix.de ([193.142.43.55]:51322 "EHLO galois.linutronix.de" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S230094AbhCIIpg (ORCPT ); Tue, 9 Mar 2021 03:45:36 -0500 Message-Id: <20210309084241.783936921@linutronix.de> DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020; t=1615279534; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: references:references; bh=4ZkB40PRvDpu0j2eO3bdXGRRAGc3lWp6vGTyvByr3WU=; b=VcarJNiF3W/kOySvc+Kvt2sQr5CNHHpp+0KYJEleYBLkSSGLsDjUwbCZ+ttJ66D0Q1ispq LuRXtaqhWDyEut2StVllxi6+rFKscZM/LnQ7WRE38ws1p90R5jOzjF3RGp8xTp1gVoWSa0 AFlD1vHkzSo1ZnTK5lrFXP8+CsljZy+7SBVIkHB7ZpzUMvgg9a8CuTb8Qg8LFpXXp1u+5r kxo6StGdFp30rNx+PoJZH29hxZ8OVFJMuEBiHq1Sk/221OQwzxW8wU2qLCqDHq5LytyQq/ +GfzqO8TQeQ/UAx+e4qL3/amdtsXJ+7A3seZTJd4Z3dgN2l9d2EEZfnQePdMXQ== DKIM-Signature: v=1; a=ed25519-sha256; c=relaxed/relaxed; d=linutronix.de; s=2020e; t=1615279534; h=from:from:reply-to:subject:subject:date:date:message-id:message-id: to:to:cc:cc:mime-version:mime-version:content-type:content-type: content-transfer-encoding:content-transfer-encoding: references:references; bh=4ZkB40PRvDpu0j2eO3bdXGRRAGc3lWp6vGTyvByr3WU=; b=jIsPkF+4WMvgAlsbmhzYBMM16NCTQ90FLvCon97O1Nn0XD+z/XvKPcjTwIPn9fDlcPJR+N 2rD7FRipxQ1yX2Bw== Date: Tue, 09 Mar 2021 09:42:08 +0100 From: Thomas Gleixner To: LKML Cc: Frederic Weisbecker , Sebastian Andrzej Siewior , "Ahmed S. Darwish" , Peter Zijlstra , Denis Kirjanov , "David S. Miller" , Jakub Kicinski , netdev@vger.kernel.org, ath9k-devel@qca.qualcomm.com, Kalle Valo , linux-wireless@vger.kernel.org, Chas Williams <3chas3@gmail.com>, linux-atm-general@lists.sourceforge.net, "K. Y. Srinivasan" , Haiyang Zhang , Stephen Hemminger , Wei Liu , Lorenzo Pieralisi , Rob Herring , Bjorn Helgaas , linux-hyperv@vger.kernel.org, linux-pci@vger.kernel.org, Stefan Richter , linux1394-devel@lists.sourceforge.net Subject: [patch 05/14] tasklets: Replace spin wait in tasklet_unlock_wait() References: <20210309084203.995862150@linutronix.de> MIME-Version: 1.0 Content-transfer-encoding: 8-bit Precedence: bulk List-ID: X-Mailing-List: linux-pci@vger.kernel.org From: Peter Zijlstra tasklet_unlock_wait() spin waits for TASKLET_STATE_RUN to be cleared. This is wasting CPU cycles in a tight loop which is especially painful in a guest when the CPU running the tasklet is scheduled out. tasklet_unlock_wait() is invoked from tasklet_kill() which is used in teardown paths and not performance critical at all. Replace the spin wait with wait_var_event(). There are no users of tasklet_unlock_wait() which are invoked from atomic contexts. The usage in tasklet_disable() has been replaced temporarily with the spin waiting variant until the atomic users are fixed up and will be converted to the sleep wait variant later. Signed-off-by: Peter Zijlstra Signed-off-by: Thomas Gleixner --- include/linux/interrupt.h | 13 ++----------- kernel/softirq.c | 18 ++++++++++++++++++ 2 files changed, 20 insertions(+), 11 deletions(-) --- a/include/linux/interrupt.h +++ b/include/linux/interrupt.h @@ -664,17 +664,8 @@ static inline int tasklet_trylock(struct return !test_and_set_bit(TASKLET_STATE_RUN, &(t)->state); } -static inline void tasklet_unlock(struct tasklet_struct *t) -{ - smp_mb__before_atomic(); - clear_bit(TASKLET_STATE_RUN, &(t)->state); -} - -static inline void tasklet_unlock_wait(struct tasklet_struct *t) -{ - while (test_bit(TASKLET_STATE_RUN, &t->state)) - cpu_relax(); -} +void tasklet_unlock(struct tasklet_struct *t); +void tasklet_unlock_wait(struct tasklet_struct *t); /* * Do not use in new code. Waiting for tasklets from atomic contexts is --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -25,6 +25,7 @@ #include #include #include +#include #include @@ -621,6 +622,23 @@ void tasklet_kill(struct tasklet_struct } EXPORT_SYMBOL(tasklet_kill); +#ifdef CONFIG_SMP +void tasklet_unlock(struct tasklet_struct *t) +{ + smp_mb__before_atomic(); + clear_bit(TASKLET_STATE_RUN, &t->state); + smp_mb__after_atomic(); + wake_up_var(&t->state); +} +EXPORT_SYMBOL_GPL(tasklet_unlock); + +void tasklet_unlock_wait(struct tasklet_struct *t) +{ + wait_var_event(&t->state, !test_bit(TASKLET_STATE_RUN, &t->state)); +} +EXPORT_SYMBOL_GPL(tasklet_unlock_wait); +#endif + void __init softirq_init(void) { int cpu;