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From: Ingo Molnar <mingo@kernel.org>
To: Vaibhav Nagarnaik <vnagarnaik@google.com>
Cc: "H. Peter Anvin" <hpa@zytor.com>,
	Steven Rostedt <rostedt@goodmis.org>,
	Frederic Weisbecker <fweisbec@gmail.com>,
	Thomas Gleixner <tglx@linutronix.de>,
	Ingo Molnar <mingo@redhat.com>, David Sharp <dhsharp@google.com>,
	Justin Teravest <teravest@google.com>,
	Laurent Chavey <chavey@google.com>,
	x86@kernel.org, linux-kernel@vger.kernel.org
Subject: Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler
Date: Thu, 29 Mar 2012 08:20:31 +0200	[thread overview]
Message-ID: <20120329062031.GB1376@gmail.com> (raw)
In-Reply-To: <CAL26m8+zbbqngfK0fYb+A2UBQ1fZ9Uxrf4VLWqU1VuMzkcF4xw@mail.gmail.com>


* Vaibhav Nagarnaik <vnagarnaik@google.com> wrote:

> On Wed, Mar 28, 2012 at 7:43 PM, H. Peter Anvin <hpa@zytor.com> wrote:
> > But instead you add a penalty for every syscall, even if tracing is
> > disabled.  Not cool.
> 
> I just ran a small test binary which calls syscall(SYS_getuid) in a
> tight loop and calculates the latency per syscall.
> 
> Without my patch: it is 70 ns/call
> With my patch: it is 83 ns/call
> 
> So yes, it does add a bit of latency to the syscall even if 
> tracing is disabled. I wonder if I can change the redirection 
> function so that it doesn't add so much latency.

There's a really simple rule for anything tracing/debugging 
related: and syscalls don't add *ANY* kind of latency to the 
non-tracing case. That is true of the current syscall tracing 
bits, they work via a TIF flag and don't add any latency.

Thanks,

	Ingo

  parent reply	other threads:[~2012-03-29  6:20 UTC|newest]

Thread overview: 29+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2012-03-26 18:39 [PATCH 0/6] Enhance and speed up syscall tracing Vaibhav Nagarnaik
2012-03-26 18:39 ` [PATCH 1/6] trace: syscalls.h - cleanup and simplify SYSCALL_METADATA() Vaibhav Nagarnaik
2012-03-26 18:39 ` [PATCH 2/6] trace: add support for 32 bit compat syscalls on x86_64 Vaibhav Nagarnaik
2012-03-27  4:49   ` H. Peter Anvin
2012-03-28 21:10     ` Vaibhav Nagarnaik
2012-03-28 21:11       ` Vaibhav Nagarnaik
2012-03-28 23:00         ` Vaibhav Nagarnaik
2012-03-26 18:39 ` [PATCH 3/6] trace: Refactor ftrace syscall macros to make them more readable Vaibhav Nagarnaik
2012-03-26 18:39 ` [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler Vaibhav Nagarnaik
2012-03-27  5:00   ` H. Peter Anvin
2012-03-28 18:23     ` Vaibhav Nagarnaik
2012-03-29  2:43       ` H. Peter Anvin
2012-03-29  2:59         ` Steven Rostedt
2012-03-29  3:15           ` H. Peter Anvin
2012-03-29  3:02         ` Vaibhav Nagarnaik
2012-03-29  3:16           ` H. Peter Anvin
2012-03-29  6:20           ` Ingo Molnar [this message]
2012-03-29 19:02             ` Vaibhav Nagarnaik
2012-03-29 19:12               ` H. Peter Anvin
2012-03-29 19:43                 ` Vaibhav Nagarnaik
2012-03-29 20:06                   ` H. Peter Anvin
2012-03-29 22:40                     ` David Sharp
2012-03-29 22:44                       ` H. Peter Anvin
2012-03-30 12:06                       ` Frederic Weisbecker
2012-03-30 11:57                     ` Frederic Weisbecker
2012-03-29 22:44                 ` David Sharp
2012-03-29 22:48                   ` H. Peter Anvin
2012-03-26 18:39 ` [PATCH 5/6] trace: raw_syscalls: Mark compat syscalls in the MSB of the syscall number Vaibhav Nagarnaik
2012-03-26 18:39 ` [PATCH 6/6] trace: get rid of the enabled_*_syscalls bitmaps Vaibhav Nagarnaik

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