linux-kernel - stat benchmark

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Message-ID: <ye8wsmnezq9.fsf@camel05.daimi.au.dk>
Date:	24 Apr 2008 22:59:10 +0200
From:	Soeren Sandmann <sandmann@...mi.au.dk>
To:	linux-kernel@...r.kernel.org
Subject: stat benchmark

At

    http://www.daimi.au.dk/~sandmann/stat-benchmark.c

there is a simple program that will measure the time it takes to stat
every file in the current directory with a cold cache.

This is essentially what applications do in a number of common cases
such as "ls -l", nautilus opening a directory, or an "open file"
dialog being showed.

Unfortunately, performance of that operation kinda sucks. On my system
(ext3), it produces:

    c-24-61-65-93:~% sudo ./a.out 
    Time to readdir(): 0.307671 s
    Time to stat 2349 files: 8.203693 s

8 seconds is about 80 times slower than what a user perceives as
"instantly" and slow enough that we really should display a progress
bar if it can't be fixed.

So I am looking for ways to improve this.

Under the theory that disk seeks are killing us, one idea is to add a
'multistat' system call that would allow statting of many files at a
time, which would give the disk scheduler more to work with. 

Possibly the same thing would need to be done for the getxattr
information.

Does this sound like a reasonable idea?

Thanks,
Soren
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