From: Steven Rostedt <rostedt@goodmis.org>
To: Masami Hiramatsu <mhiramat@kernel.org>
Cc: Brendan Gregg <brendan.d.gregg@gmail.com>,
Alexei Starovoitov <ast@kernel.org>,
Ingo Molnar <mingo@kernel.org>,
bpf@vger.kernel.org, linux-kernel@vger.kernel.org,
Daniel Borkmann <daniel@iogearbox.net>,
Arnaldo Carvalho de Melo <acme@kernel.org>,
"David S . Miller" <davem@davemloft.net>,
paulmck@kernel.org, joel@joelfernandes.org,
"Naveen N . Rao" <naveen.n.rao@linux.ibm.com>,
Anil S Keshavamurthy <anil.s.keshavamurthy@intel.com>
Subject: Re: [RFT PATCH 04/13] kprobes: Make optimizer delay to 1 second
Date: Wed, 22 Jan 2020 07:11:15 -0500 [thread overview]
Message-ID: <20200122071115.28e3c763@gandalf.local.home> (raw)
In-Reply-To: <20200122162317.0299cf722dd618147d97e89c@kernel.org>
On Wed, 22 Jan 2020 16:23:17 +0900
Masami Hiramatsu <mhiramat@kernel.org> wrote:
> On Tue, 21 Jan 2020 19:29:05 -0500
> Steven Rostedt <rostedt@goodmis.org> wrote:
>
> > On Thu, 16 Jan 2020 23:44:52 +0900
> > Masami Hiramatsu <mhiramat@kernel.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.
>
> Yes, I had introduced this 5 jiffies delay for multiple probe registration
> and unregistration like systemtap, which will use array-based interface to
> register/unregister. In that case, 5 jiffies will be enough for the delay
> to wait for other kprobe registration/unregsitration.
>
> However, since perf and ftrace register/unregister probes one-by-one with
> RCU synchronization interval, the optimizer will be started before
> finishing to register/unregister all probes.
> And the optimizer locks kprobe_mutex a while -- RCU-tasks synchronization.
> Since the kprobe_mutex is also involved in disabling kprobes, this also
> stops probe-event disabling.
>
> Maybe 5 jiffies is enough for adding/removing a few probe events, but
> not enough for dozens of probe events.
>
Perhaps we should have a mechanism that can detect new probes being
added, and just continue to delay the optimization, instead of having
some arbitrary delay.
-- Steve
next prev parent reply other threads:[~2020-01-22 12:11 UTC|newest]
Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-16 14:44 [RFT PATCH 00/13] tracing: kprobes: Introduce async unregistration Masami Hiramatsu
2020-01-16 14:44 ` [RFT PATCH 01/13] kprobes: Fix to protect kick_kprobe_optimizer() by kprobe_mutex Masami Hiramatsu
2020-01-16 14:44 ` [RFT PATCH 02/13] kprobes: Remove redundant arch_disarm_kprobe() call Masami Hiramatsu
2020-01-16 14:44 ` [RFT PATCH 03/13] kprobes: Postpone optimizer until a bunch of probes (un)registered Masami Hiramatsu
2020-01-16 14:44 ` [RFT PATCH 04/13] kprobes: Make optimizer delay to 1 second Masami Hiramatsu
2020-01-22 0:29 ` Steven Rostedt
2020-01-22 7:23 ` Masami Hiramatsu
2020-01-22 12:11 ` Steven Rostedt [this message]
2020-01-22 13:12 ` Masami Hiramatsu
2020-01-22 16:54 ` Paul E. McKenney
2020-01-23 1:33 ` Masami Hiramatsu
2020-01-23 2:26 ` Paul E. McKenney
2020-01-23 6:13 ` Masami Hiramatsu
2020-01-23 10:03 ` Paul E. McKenney
2020-01-16 14:45 ` [RFT PATCH 05/13] tracing/kprobe: Use call_rcu to defer freeing event_file_link Masami Hiramatsu
2020-01-27 15:02 ` kbuild test robot
2020-01-27 15:02 ` [RFC PATCH] tracing/kprobe: trace_kprobe_disabled_finished can be static kbuild test robot
2020-01-28 15:02 ` Masami Hiramatsu
2020-01-16 14:45 ` [RFT PATCH 06/13] kprobes: Enable kprobe-booster with CONFIG_PREEMPT=y Masami Hiramatsu
2020-01-16 14:45 ` [RFT PATCH 07/13] kprobes: Use normal list traversal API if a mutex is held Masami Hiramatsu
2020-01-16 14:45 ` [RFT PATCH 08/13] kprobes: Use workqueue for reclaiming kprobe insn cache pages Masami Hiramatsu
2020-01-16 14:45 ` [RFT PATCH 09/13] kprobes: Free kprobe_insn_page asynchronously Masami Hiramatsu
2020-01-16 14:45 ` [RFT PATCH 10/13] kprobes: Make free_*insn_slot() mutex-less Masami Hiramatsu
2020-01-16 14:46 ` [RFT PATCH 11/13] kprobes: Add asynchronous unregistration APIs Masami Hiramatsu
2020-01-16 14:46 ` [RFT PATCH 12/13] tracing/kprobe: Free probe event asynchronously Masami Hiramatsu
2020-01-16 14:46 ` [RFT PATCH 13/13] tracing/kprobe: perf_event: Remove local kprobe " Masami Hiramatsu
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