From patchwork Tue May 23 17:22:46 2023 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Daniel Bristot de Oliveira X-Patchwork-Id: 13252706 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 48FD2C77B75 for ; Tue, 23 May 2023 17:23:30 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S238088AbjEWRX3 (ORCPT ); Tue, 23 May 2023 13:23:29 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:54106 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S238087AbjEWRXZ (ORCPT ); Tue, 23 May 2023 13:23:25 -0400 Received: from dfw.source.kernel.org (dfw.source.kernel.org [IPv6:2604:1380:4641:c500::1]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 6061390; Tue, 23 May 2023 10:23:00 -0700 (PDT) Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by dfw.source.kernel.org (Postfix) with ESMTPS id 91B6063510; Tue, 23 May 2023 17:22:58 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 007E3C4339C; Tue, 23 May 2023 17:22:55 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=k20201202; t=1684862578; bh=byVxc842f341YKhh/NiVACrDBf3a2XL1VPHU0WLutWM=; h=From:To:Cc:Subject:Date:In-Reply-To:References:From; b=V7sjBh6vtLNKIOluj10arzB7akVjLk7/GZtNyp6H9vVDXtCOj2B+/Uf3SLnJ2s2un fipDDmjP/8LHJqucnYO0xn8fjYqKSl7uu9c0tQg0FrzaA8+zFnTbNWGnPppCMxW8EN uUvJNLsf6iFjHHXqBf/kResL5ElwD0AI5N7yPAbM+JuXdRP7CoBKVy1MbLeplP0y7W cqan4hpey5X+09b/5v3VyN4JhhhITxp+lTwFrH1PEo1Vyj7BqFKpiBVit9gGVNHdxu Dlfdu2QDjteTx8yEHrVs6lQx7RqLZjfx1pGD3Ox2pIYMsRHmGr9cYUforSpaTsv4vo 4o6IrGzJCHlPg== From: Daniel Bristot de Oliveira To: linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Steven Rostedt Cc: Juri Lelli , William White , Daniel Bristot de Oliveira , Masami Hiramatsu , Jonathan Corbet Subject: [PATCH V2 1/3] tracing/osnoise: Switch from PF_NO_SETAFFINITY to migrate_disable Date: Tue, 23 May 2023 19:22:46 +0200 Message-Id: X-Mailer: git-send-email 2.38.1 In-Reply-To: References: MIME-Version: 1.0 Precedence: bulk List-ID: X-Mailing-List: linux-trace-kernel@vger.kernel.org Currently, osnoise/timerlat threads run with PF_NO_SETAFFINITY set. It works well, however, cgroups do not allow PF_NO_SETAFFINITY threads to be accepted, and this creates a limitation to osnoise/timerlat. To avoid this limitation, disable migration of the threads as soon as they start to run, and then clean the PF_NO_SETAFFINITY flag (still) used during thread creation. If for some reason a thread migration is requested, e.g., via sched_settafinity, the tracer thread will notice and exit. Cc: Steven Rostedt Cc: Daniel Bristot de Oliveira Cc: Masami Hiramatsu Cc: Jonathan Corbet Signed-off-by: Daniel Bristot de Oliveira --- kernel/trace/trace_osnoise.c | 68 ++++++++++++++++++++++++++++++++++++ 1 file changed, 68 insertions(+) diff --git a/kernel/trace/trace_osnoise.c b/kernel/trace/trace_osnoise.c index e97e3fa5cbed..c265ec5f1726 100644 --- a/kernel/trace/trace_osnoise.c +++ b/kernel/trace/trace_osnoise.c @@ -1545,6 +1545,39 @@ static void osnoise_sleep(void) } } +/* + * osnoise_migration_pending - checks if the task needs to migrate + * + * osnoise/timerlat threads are per-cpu. If there is a pending request to + * migrate the thread away from the current CPU, something bad has happened. + * Play the good citizen and leave. + * + * Returns 0 if it is safe to continue, 1 otherwise. + */ +static inline int osnoise_migration_pending(void) +{ + if (!current->migration_pending) + return 0; + + /* + * If migration is pending, there is a task waiting for the + * tracer to enable migration. The tracer does not allow migration, + * thus: taint and leave to unblock the blocked thread. + */ + osnoise_taint("migration requested to osnoise threads, leaving."); + + /* + * Unset this thread from the threads managed by the interface. + * The tracers are responsible for cleaning their env before + * exiting. + */ + mutex_lock(&interface_lock); + this_cpu_osn_var()->kthread = NULL; + mutex_unlock(&interface_lock); + + return 1; +} + /* * osnoise_main - The osnoise detection kernel thread * @@ -1553,12 +1586,29 @@ static void osnoise_sleep(void) */ static int osnoise_main(void *data) { + unsigned long flags; + + /* + * This thread was created pinned to the CPU using PF_NO_SETAFFINITY. + * The problem is that cgroup does not allow PF_NO_SETAFFINITY thread. + * + * To work around this limitation, disable migration and remove the + * flag. + */ + migrate_disable(); + raw_spin_lock_irqsave(¤t->pi_lock, flags); + current->flags &= ~(PF_NO_SETAFFINITY); + raw_spin_unlock_irqrestore(¤t->pi_lock, flags); while (!kthread_should_stop()) { + if (osnoise_migration_pending()) + break; + run_osnoise(); osnoise_sleep(); } + migrate_enable(); return 0; } @@ -1706,6 +1756,7 @@ static int timerlat_main(void *data) struct timerlat_variables *tlat = this_cpu_tmr_var(); struct timerlat_sample s; struct sched_param sp; + unsigned long flags; u64 now, diff; /* @@ -1714,6 +1765,18 @@ static int timerlat_main(void *data) sp.sched_priority = DEFAULT_TIMERLAT_PRIO; sched_setscheduler_nocheck(current, SCHED_FIFO, &sp); + /* + * This thread was created pinned to the CPU using PF_NO_SETAFFINITY. + * The problem is that cgroup does not allow PF_NO_SETAFFINITY thread. + * + * To work around this limitation, disable migration and remove the + * flag. + */ + migrate_disable(); + raw_spin_lock_irqsave(¤t->pi_lock, flags); + current->flags &= ~(PF_NO_SETAFFINITY); + raw_spin_unlock_irqrestore(¤t->pi_lock, flags); + tlat->count = 0; tlat->tracing_thread = false; @@ -1731,6 +1794,7 @@ static int timerlat_main(void *data) osn_var->sampling = 1; while (!kthread_should_stop()) { + now = ktime_to_ns(hrtimer_cb_get_time(&tlat->timer)); diff = now - tlat->abs_period; @@ -1749,10 +1813,14 @@ static int timerlat_main(void *data) if (time_to_us(diff) >= osnoise_data.stop_tracing_total) osnoise_stop_tracing(); + if (osnoise_migration_pending()) + break; + wait_next_period(tlat); } hrtimer_cancel(&tlat->timer); + migrate_enable(); return 0; } #else /* CONFIG_TIMERLAT_TRACER */