linux-kernel - Query for time tracking between userspace and kernelspace

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Date:	Fri, 4 Apr 2014 00:02:21 -0700
From:	noman pouigt <variksla@...il.com>
To:	john.stultz@...aro.org, Thomas Gleixner <tglx@...utronix.de>,
	Stephen Boyd <sboyd@...eaurora.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	Steven Rostedt <rostedt@...dmis.org>,
	Michael Opdenacker <michael.opdenacker@...e-electrons.com>,
	Joe Perches <joe@...ches.com>, Petr Mladek <pmladek@...e.cz>,
	linux-kernel@...r.kernel.org, leiwen@...vell.com
Subject: Query for time tracking between userspace and kernelspace

Hello,

Probably this question belongs to kernelnewbies
list but I think i will get accurate answer from here.

I am doing some optimization in kernel video driver
code to reduce the latency from the time buffer
is given to the time it is displayed.

Userspace:
t1 = gettimeofday()

Kernelspace:
t2 = do_gettimeofday()

Using debugfs i am copying t2 to userspace and
subtracting the result.

latency = t2 - t1

Would this be accurate? I know there is context
switch involved and other stuff but this is the method
i came up with. Any better way?

System: ARM (Android)
Kernel- 3.10
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