linux-kernel - Re: [RFT PATCH 04/13] kprobes: Make optimizer delay to 1 second

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Message-ID: <20200121192905.0f001c61@gandalf.local.home>
Date:   Tue, 21 Jan 2020 19:29:05 -0500
From:   Steven Rostedt <rostedt@...dmis.org>
To:     Masami Hiramatsu <mhiramat@...nel.org>
Cc:     Brendan Gregg <brendan.d.gregg@...il.com>,
        Alexei Starovoitov <ast@...nel.org>,
        Ingo Molnar <mingo@...nel.org>, bpf@...r.kernel.org,
        linux-kernel@...r.kernel.org,
        Daniel Borkmann <daniel@...earbox.net>,
        Arnaldo Carvalho de Melo <acme@...nel.org>,
        "David S . Miller" <davem@...emloft.net>, paulmck@...nel.org,
        joel@...lfernandes.org,
        "Naveen N . Rao" <naveen.n.rao@...ux.ibm.com>,
        Anil S Keshavamurthy <anil.s.keshavamurthy@...el.com>
Subject: Re: [RFT PATCH 04/13] kprobes: Make optimizer delay to 1 second

On Thu, 16 Jan 2020 23:44:52 +0900
Masami Hiramatsu <mhiramat@...nel.org> wrote:

> Since the 5 jiffies delay for the optimizer is too
> short to wait for other probes, make it longer,
> like 1 second.

Hi Masami,

Can you explain more *why* 5 jiffies is too short.

Thanks!

-- Steve

> 
> Signed-off-by: Masami Hiramatsu <mhiramat@...nel.org>
> ---
>  kernel/kprobes.c |    3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
> 
> diff --git a/kernel/kprobes.c b/kernel/kprobes.c
> index 0dacdcecc90f..9c6e230852ad 100644
> --- a/kernel/kprobes.c
> +++ b/kernel/kprobes.c
> @@ -469,7 +469,8 @@ static int kprobe_optimizer_queue_update;
>  
>  static void kprobe_optimizer(struct work_struct *work);
>  static DECLARE_DELAYED_WORK(optimizing_work, kprobe_optimizer);
> -#define OPTIMIZE_DELAY 5
> +/* Wait 1 second for starting optimization */
> +#define OPTIMIZE_DELAY HZ
>  
>  /*
>   * Optimize (replace a breakpoint with a jump) kprobes listed on