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From: Masami Hiramatsu <mhiramat@kernel.org>
To: Steven Rostedt <rostedt@goodmis.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 22:12:40 +0900	[thread overview]
Message-ID: <20200122221240.cef447446785f46862fee97a@kernel.org> (raw)
In-Reply-To: <20200122071115.28e3c763@gandalf.local.home>

On Wed, 22 Jan 2020 07:11:15 -0500
Steven Rostedt <rostedt@goodmis.org> wrote:

> 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.

Yes, that is what [03/13] does :) 
Anyway, it seems that the RCU-synchronization takes more than 5 jiffies.
And in that case, [03/13] still doesn't work. That's why I added this patch
after that.

Thank you,

-- 
Masami Hiramatsu <mhiramat@kernel.org>

  reply	other threads:[~2020-01-22 13:12 UTC|newest]

Thread overview: 29+ 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
2020-01-22 13:12         ` Masami Hiramatsu [this message]
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     ` kbuild test robot
2020-01-27 15:02   ` [RFC PATCH] tracing/kprobe: trace_kprobe_disabled_finished can be static kbuild test robot
2020-01-27 15:02     ` kbuild test robot
2020-01-28 15:02     ` Masami Hiramatsu
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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