linux-kernel - Re: [RFC][PATCH RT] rwsem_rt: Another (more sane) approach to mulit reader rt locks

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Date:	Tue, 15 May 2012 12:26:20 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	LKML <linux-kernel@...r.kernel.org>
Cc:	RT <linux-rt-users@...r.kernel.org>,
	Thomas Gleixner <tglx@...utronix.de>,
	Clark Williams <williams@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>
Subject: Re: [RFC][PATCH RT] rwsem_rt: Another (more sane) approach to mulit
 reader rt locks

On Tue, 2012-05-15 at 10:03 -0400, Steven Rostedt wrote:

> I'll see if I can get some numbers to see how this fixes the issues with
> multi threads on big boxes.
> 

I couldn't get access to the big box, so I wrote my own test. The
attached program is what I used. It creates 400 threads and allocates a
memory range (with mmap) of 10 gigs. Then it runs all 400 threads, where
each is fighting to read this new memory. Causing lots of page faults.

I tested on a 4 CPU box with 3.4.0-rc7-rt6:

Without the patch:

map=10737418240
time = 11302617 usecs
map=10737418240
time = 11229341 usecs
map=10737418240
time = 11171463 usecs
map=10737418240
time = 11435549 usecs
map=10737418240
time = 11299086 usecs

With the patch:

map=10737418240
time = 6493796 usecs
map=10737418240
time = 6726186 usecs
map=10737418240
time = 3978194 usecs
map=10737418240
time = 6796688 usecs

So it went from roughly 11 secs to 6 secs (even had one 4sec run). This
shows that it sped up the fault access by almost half.

-- Steve

View attachment "faultme.c" of type "text/x-csrc" (2327 bytes)