linux-kernel - Problem: CPU sleep when calling a function in another object for the first time.

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Message-ID: <E9FB75D95739914DBDEDC1867C740F4FD4E64C@ITLHZEXCH01.us.utstar.com>
Date:	Tue, 16 Oct 2007 05:11:07 +0800
From:	"John Marconi" <john.marconi@...tar.com>
To:	<linux-kernel@...r.kernel.org>
Subject: Problem:  CPU sleep when calling a function in another object for the first time.

Hello,

I have been seeing a problem in which one of my CPUs goes to sleep for
40ms in the middle of running a user-space program.  The problem occurs
when I have a function in object file X call another function in object
file Y.  If I add a gettimeofday right before the function call occurs,
and then also right at the beginning of the called function, I see a
40ms delay.  This only occurs on the first call to any function in file
Y.  Once a function in file Y is called, all other calls to functions in
this file are immediate.

I have added a kernel profiler to the timer interrupt of this CPU - and
find that during this 40ms period, the CPU is in r4k_wait - which looks
like cpu_idle is running.  It almost seems like file Y is being loaded
into memory to be used.

The program in question is using pthreads and each thread is on a
separate CPU.  Each CPU is dedicated to running a single thread and
nothing else.  The files X and Y are two object files linked into a
single ELF binary.  The kernel version is 2.6.14 and this is a MIPS
based processor.

Does anyone have any ideas why this delay might be occurring?

Thank you in advance,
John
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