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 181CEC197A0 for ; Mon, 20 Nov 2023 20:28:43 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S230035AbjKTU2j convert rfc822-to-8bit (ORCPT ); Mon, 20 Nov 2023 15:28:39 -0500 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:42274 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S229500AbjKTU2h (ORCPT ); Mon, 20 Nov 2023 15:28:37 -0500 Received: from mail-pj1-f48.google.com (mail-pj1-f48.google.com [209.85.216.48]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 7C8EBC3 for ; Mon, 20 Nov 2023 12:28:34 -0800 (PST) Received: by mail-pj1-f48.google.com with SMTP id 98e67ed59e1d1-27ff7fe7fbcso3769229a91.1 for ; Mon, 20 Nov 2023 12:28:34 -0800 (PST) X-Google-DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=1e100.net; s=20230601; t=1700512114; x=1701116914; h=content-transfer-encoding:cc:to:subject:message-id:date:from :in-reply-to:references:mime-version:x-gm-message-state:from:to:cc :subject:date:message-id:reply-to; bh=PAUXEY25pcgFJPPMr5X8QK/ZolpU8TE7YcrDkatwu6s=; b=ddnkell22j4pP+rUYQdOtfYfqL+PoL0JNaEVF9dOLZ9hEITuiD98hNVE56m8AHDxCP dP3awVlE6aBuSoG4Bsfz8KMEfFSI5QtzjVmXM7PM+S3lhdZmNdWHjyJyefNhePDfXpQn x2L9JUiu7HD1R53rTghW+1BPygsnh7dj3ToJIP5ZJDNU6TkEDsjdZM2ZScwgul6Zl1eg o/DLadjNZlmT78Aph1e/KSQQS/9kATZgs4hiiMRuetGO8SFPIdsyGLH5rsnCQZamW+PO qRvzyKyg4F6HIApQyfHQcerbVfcQsSox91y++qSx7UFKHd0v4OM46ONIlE63qOquUsXq HVfQ== X-Gm-Message-State: AOJu0YxHduEYJNC3izVUegTLdzMiUUzvRE/HWFWX5NeElsgPbCAoPb+T reYQjXuMw4buoosCpCBw8ET9epLxO1vJrDWChsM= X-Google-Smtp-Source: AGHT+IFjJaIdl7rl7XrC7OqYukh73/zgvAGS1DpoMNPVOIdITESLNeauhhDe8BD3rBYF0zpa1RFk+vt2buB1GdNQsss= X-Received: by 2002:a17:90b:4b8d:b0:27d:3f0c:f087 with SMTP id lr13-20020a17090b4b8d00b0027d3f0cf087mr8832482pjb.25.1700512113834; Mon, 20 Nov 2023 12:28:33 -0800 (PST) MIME-Version: 1.0 References: <20231108215322.2845536-1-namhyung@kernel.org> In-Reply-To: <20231108215322.2845536-1-namhyung@kernel.org> From: Namhyung Kim Date: Mon, 20 Nov 2023 12:28:22 -0800 Message-ID: Subject: Re: [PATCH] locking/percpu-rwsem: Trigger contention tracepoints only if contended To: Peter Zijlstra , Ingo Molnar , Will Deacon Cc: Waiman Long , Boqun Feng , LKML Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Ping! On Wed, Nov 8, 2023 at 1:53 PM Namhyung Kim wrote: > > 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 >