linux-kernel - Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler

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Message-ID: <CAL26m8+zbbqngfK0fYb+A2UBQ1fZ9Uxrf4VLWqU1VuMzkcF4xw@mail.gmail.com>
Date:	Wed, 28 Mar 2012 20:02:54 -0700
From:	Vaibhav Nagarnaik <vnagarnaik@...gle.com>
To:	"H. Peter Anvin" <hpa@...or.com>
Cc:	Steven Rostedt <rostedt@...dmis.org>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	David Sharp <dhsharp@...gle.com>,
	Justin Teravest <teravest@...gle.com>,
	Laurent Chavey <chavey@...gle.com>, x86@...nel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH 4/6] trace: trace syscall in its handler not from ptrace handler

On Wed, Mar 28, 2012 at 7:43 PM, H. Peter Anvin <hpa@...or.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.

But if it doesn't seem to help, then I will not push this patch.



Vaibhav Nagarnaik
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