linux-ext4 - Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent cache

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Date:	Fri, 13 Apr 2012 12:26:53 -0700
From:	Tim Chen <tim.c.chen@...ux.intel.com>
To:	Ted Ts'o <tytso@....edu>
Cc:	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andi Kleen <andi@...stfloor.org>,
	Vivek Haldar <haldar@...gle.com>,
	Andreas Dilger <adilger@...ger.ca>, linux-ext4@...r.kernel.org
Subject: Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent
 cache

On Fri, 2012-04-13 at 14:37 -0400, Ted Ts'o wrote:
> On Fri, Apr 13, 2012 at 11:31:16AM -0700, Tim Chen wrote:
> > 
> > Benchmark is working on files on normal hard disk.  
> > However, I have I have a large number
> > of processes (80 processes, one for each cpu), each reading
> > a separate mmaped file.  The files are in the same directory.
> > That makes cache line bouncing on the counters particularly bad
> > due to the large number of processes running.
> 
> OK, so this is with an 80 CPU machine?
> 
> And when you say 20% speed up, do you mean to say we are actually
> being CPU constrained when reading from files on a normal hard disk?
> 

The files are sparse files.  So the amount of IO is limited and we are
not IO constrained.  

Tim

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