[<prev] [next>] [<thread-prev] [thread-next>] [day] [month] [year] [list]
Message-ID: <20230929110657.7a4b38ef@rorschach.local.home>
Date: Fri, 29 Sep 2023 11:06:57 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Clément Léger <cleger@...osinc.com>
Cc: Masami Hiramatsu <mhiramat@...nel.org>,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
Atish Patra <atishp@...osinc.com>
Subject: Re: [PATCH] tracing: relax trace_event_eval_update() execution with
schedule()
On Fri, 29 Sep 2023 16:13:48 +0200
Clément Léger <cleger@...osinc.com> 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.
>
> 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.
>
> Signed-off-by: Clément Léger <cleger@...osinc.com>
> ---
> 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..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/
Powered by blists - more mailing lists