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 Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by smtp.lore.kernel.org (Postfix) with ESMTP id 5D971C4332F for ; Wed, 8 Nov 2023 21:53:27 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230202AbjKHVx2 (ORCPT ); Wed, 8 Nov 2023 16:53:28 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:32802 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229460AbjKHVx0 (ORCPT ); Wed, 8 Nov 2023 16:53:26 -0500 Received: from mail-pg1-x529.google.com (mail-pg1-x529.google.com [IPv6:2607:f8b0:4864:20::529]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 57B7B258A for ; Wed, 8 Nov 2023 13:53:24 -0800 (PST) Received: by mail-pg1-x529.google.com with SMTP id 41be03b00d2f7-5bd0631f630so160181a12.0 for ; Wed, 08 Nov 2023 13:53:24 -0800 (PST) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=20230601; t=1699480404; x=1700085204; darn=vger.kernel.org; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:sender:from:to:cc:subject:date:message-id:reply-to; bh=8+1RUn6ye/V5oCXpT4AXN5Yt2m+B7UnFQxMDOfZORrg=; b=XcVaQsRAQdI7aRmQVwJ0NyQGgdhNuLJ61Cgdkn9wCXn30j5CmhU+lIo5+X9g7tMnBi E8iemZZGHVFoKGwpXh+WWbY6FOOjKsvN9EI7EIz2LWehttpGZU8/LVH4ngT7AffDlKUS PdwI+Gokukiah6uC6L9PEb6IrPFcMsyzJzZArAd+BJcELZ8FIRO9F1LPU3x54CSPZJlp FhZuE2XwDoyVR56ihP5IoyzM7X+60UlxMYyTe8MqsULsZ9r9BIwkGUSSaIQbAQR7zCoc b9fzbQpZBV105EV4VzYQf9pJtHYIbB8RFxzws2wxvou3quqqlFtJqvaQSvuJwvvJY/bb UFCw== X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1699480404; x=1700085204; h=content-transfer-encoding:mime-version:message-id:date:subject:cc :to:from:sender:x-gm-message-state:from:to:cc:subject:date :message-id:reply-to; bh=8+1RUn6ye/V5oCXpT4AXN5Yt2m+B7UnFQxMDOfZORrg=; b=uq6TX8Qqq6qvRHJnP5HCOPcODvY8LNbM5iqmBW+/iGkVNgnuFspGXUfkUZ/LGpELt3 PJmqLfd4v3kF0VzB/Odj/+OrT6n9DWr8Z3kQNmdnUj32FFObHZfzONmHRNAg4hrQkHzw iY4DjMZZ/QTy3qeYL+qefl/a2g4XpBVA7nMkvMdsjgc+T3eAn3DThbGuHqLZMMi+5uo8 h1bHHfbLo40Fyluz8Q4g3rnVhnPU7q7+VosAlq2sLxN9LQH+6eO5IBK3IoRykOAZwgQn ybiyVOXF9oa32ovPgVhl7g2I/uLR1cZv+XZZOCVrnWYkyLOBmxLV++GxdAo8zxmX3s1A ek+Q== X-Gm-Message-State: AOJu0YxZ6EneREZY//FJ4m29UEHMmoBXymwXLeomcqW9FY5r4zWNsGqE 5Wih7gtlAGHlpoPL4XiWzcEsUuKIZ8E= X-Google-Smtp-Source: AGHT+IE/XmW31pGR0Fd40lkQo3F0PWhZ1Fp3t1e0BasAmBW4Co8zM3MPBhHSzkH653j565vjM0RO7A== X-Received: by 2002:a17:90a:d717:b0:280:2a3f:9938 with SMTP id y23-20020a17090ad71700b002802a3f9938mr10158599pju.12.1699480403564; Wed, 08 Nov 2023 13:53:23 -0800 (PST) Received: from bangji.corp.google.com ([2620:15c:2c0:5:555d:a196:40f8:b293]) by smtp.gmail.com with ESMTPSA id z23-20020a17090acb1700b00280cd18c161sm4469pjt.53.2023.11.08.13.53.22 (version=TLS1_3 cipher=TLS_AES_256_GCM_SHA384 bits=256/256); Wed, 08 Nov 2023 13:53:23 -0800 (PST) Sender: Namhyung Kim From: Namhyung Kim To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Waiman Long , Boqun Feng , LKML Subject: [PATCH] locking/percpu-rwsem: Trigger contention tracepoints only if contended Date: Wed, 8 Nov 2023 13:53:22 -0800 Message-ID: <20231108215322.2845536-1-namhyung@kernel.org> X-Mailer: git-send-email 2.42.0.869.gea05f2083d-goog MIME-Version: 1.0 Content-Transfer-Encoding: 8bit Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org It mistakenly fires lock contention tracepoints always in the writer path. It should be conditional on the try lock result. Signed-off-by: Namhyung Kim --- kernel/locking/percpu-rwsem.c | 11 ++++++++--- 1 file changed, 8 insertions(+), 3 deletions(-) diff --git a/kernel/locking/percpu-rwsem.c b/kernel/locking/percpu-rwsem.c index 185bd1c906b0..6083883c4fe0 100644 --- a/kernel/locking/percpu-rwsem.c +++ b/kernel/locking/percpu-rwsem.c @@ -223,9 +223,10 @@ static bool readers_active_check(struct percpu_rw_semaphore *sem) void __sched percpu_down_write(struct percpu_rw_semaphore *sem) { + bool contended = false; + might_sleep(); rwsem_acquire(&sem->dep_map, 0, 0, _RET_IP_); - trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE); /* Notify readers to take the slow path. */ rcu_sync_enter(&sem->rss); @@ -234,8 +235,11 @@ void __sched percpu_down_write(struct percpu_rw_semaphore *sem) * Try set sem->block; this provides writer-writer exclusion. * Having sem->block set makes new readers block. */ - if (!__percpu_down_write_trylock(sem)) + if (!__percpu_down_write_trylock(sem)) { + trace_contention_begin(sem, LCB_F_PERCPU | LCB_F_WRITE); percpu_rwsem_wait(sem, /* .reader = */ false); + contended = true; + } /* smp_mb() implied by __percpu_down_write_trylock() on success -- D matches A */ @@ -247,7 +251,8 @@ void __sched percpu_down_write(struct percpu_rw_semaphore *sem) /* Wait for all active readers to complete. */ rcuwait_wait_event(&sem->writer, readers_active_check(sem), TASK_UNINTERRUPTIBLE); - trace_contention_end(sem, 0); + if (contended) + trace_contention_end(sem, 0); } EXPORT_SYMBOL_GPL(percpu_down_write); -- 2.42.0.869.gea05f2083d-goog