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 D7ECAE748E7 for ; Sat, 30 Sep 2023 20:41:10 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S233564AbjI3UlL convert rfc822-to-8bit (ORCPT ); Sat, 30 Sep 2023 16:41:11 -0400 Received: from lindbergh.monkeyblade.net ([23.128.96.19]:43404 "EHLO lindbergh.monkeyblade.net" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S231351AbjI3UlJ (ORCPT ); Sat, 30 Sep 2023 16:41:09 -0400 Received: from smtp.kernel.org (relay.kernel.org [52.25.139.140]) by lindbergh.monkeyblade.net (Postfix) with ESMTPS id 16F9DC4 for ; Sat, 30 Sep 2023 13:41:08 -0700 (PDT) Received: by smtp.kernel.org (Postfix) with ESMTPSA id EF733C433C7; Sat, 30 Sep 2023 20:41:06 +0000 (UTC) Date: Sat, 30 Sep 2023 16:41:05 -0400 From: Steven Rostedt To: linux-kernel@vger.kernel.org Cc: Masami Hiramatsu , Mark Rutland , Andrew Morton , =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= , Atish Patra Subject: Re: [for-linus][PATCH 2/4] tracing: relax trace_event_eval_update() execution with cond_resched() Message-ID: <20230930164105.534e7400@rorschach.local.home> In-Reply-To: <20230930203821.632661639@goodmis.org> References: <20230930203213.826737400@goodmis.org> <20230930203821.632661639@goodmis.org> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: 8BIT Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org [ The problem with sending email with quilt. It doesn't handle UTF-8 well :-/ ] On Sat, 30 Sep 2023 16:32:15 -0400 Steven Rostedt wrote: > From: =?UTF-8?q?Cl=C3=A9ment=20L=C3=A9ger?= > > When kernel is compiled without preemption, the eval_map_work_func() > (which calls trace_event_eval_update()) will not be preempted up to its > complete execution. This can actually cause a problem since if another > CPU call stop_machine(), the call will have to wait for the > eval_map_work_func() function to finish executing in the workqueue > before being able to be scheduled. This problem was observe on a SMP > system at boot time, when the CPU calling the initcalls executed > clocksource_done_booting() which in the end calls stop_machine(). We > observed a 1 second delay because one CPU was executing > eval_map_work_func() and was not preempted by the stop_machine() task. > > Adding a call to cond_resched() in trace_event_eval_update() allows > other tasks to be executed and thus continue working asynchronously > like before without blocking any pending task at boot time. > > Link: https://lore.kernel.org/linux-trace-kernel/20230929191637.416931-1-cleger@rivosinc.com > > Cc: Masami Hiramatsu > Signed-off-by: Clément Léger > Tested-by: Atish Patra > Reviewed-by: Atish Patra > Signed-off-by: Steven Rostedt (Google) > --- > kernel/trace/trace_events.c | 1 + > 1 file changed, 1 insertion(+) > > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index 91951d038ba4..f49d6ddb6342 100644 > --- a/kernel/trace/trace_events.c > +++ b/kernel/trace/trace_events.c > @@ -2770,6 +2770,7 @@ void trace_event_eval_update(struct trace_eval_map **map, int len) > update_event_fields(call, map[i]); > } > } > + cond_resched(); > } > up_write(&trace_event_sem); > }