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Date:	Fri, 13 Apr 2012 12:26:53 -0700
From:	Tim Chen <>
To:	Ted Ts'o <>
Cc:	Linus Torvalds <>,
	Andi Kleen <>,
	Vivek Haldar <>,
	Andreas Dilger <>,
Subject: Re: [RFC, PATCH] Avoid hot statistics cache line in ext4 extent

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.  


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