From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from smtp.kernel.org (aws-us-west-2-korg-mail-1.web.codeaurora.org [10.30.226.201]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by smtp.subspace.kernel.org (Postfix) with ESMTPS id 5D8E8C2CF for ; Fri, 29 Sep 2023 15:07:02 +0000 (UTC) Received: by smtp.kernel.org (Postfix) with ESMTPSA id 552A5C433C8; Fri, 29 Sep 2023 15:07:01 +0000 (UTC) Date: Fri, 29 Sep 2023 11:06:57 -0400 From: Steven Rostedt To: =?UTF-8?B?Q2zDqW1lbnQgTMOpZ2Vy?= Cc: Masami Hiramatsu , linux-kernel@vger.kernel.org, linux-trace-kernel@vger.kernel.org, Atish Patra Subject: Re: [PATCH] tracing: relax trace_event_eval_update() execution with schedule() Message-ID: <20230929110657.7a4b38ef@rorschach.local.home> In-Reply-To: <20230929141348.248761-1-cleger@rivosinc.com> References: <20230929141348.248761-1-cleger@rivosinc.com> X-Mailer: Claws Mail 3.17.8 (GTK+ 2.24.33; x86_64-pc-linux-gnu) Precedence: bulk X-Mailing-List: linux-trace-kernel@vger.kernel.org List-Id: List-Subscribe: List-Unsubscribe: MIME-Version: 1.0 Content-Type: text/plain; charset=UTF-8 Content-Transfer-Encoding: quoted-printable On Fri, 29 Sep 2023 16:13:48 +0200 Cl=C3=A9ment L=C3=A9ger wrote: > 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. >=20 > Adding a call to schedule() in trace_event_eval_update() allows to let > other tasks to be executed and thus continue working asynchronously like > before without blocking any pending task at boot time. >=20 > Signed-off-by: Cl=C3=A9ment L=C3=A9ger > --- > kernel/trace/trace_events.c | 1 + > 1 file changed, 1 insertion(+) >=20 > diff --git a/kernel/trace/trace_events.c b/kernel/trace/trace_events.c > index 91951d038ba4..dbdf57a081c0 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]); > } > } > + schedule(); The proper answer to this is "cond_resched()" but still, there's going to be work to get rid of all that soon [1]. But I'll take a cond_resched() now until that is implemented. -- Steve > } > up_write(&trace_event_sem); > } [1] https://lore.kernel.org/all/87cyyfxd4k.ffs@tglx/