Re: slow stat() ?

[Hans Reiser <reiser@namesys.com>]

Chris Mason wrote:

>On Mon, 2003-12-01 at 12:21, David Bernick wrote:
>  
>
>>Hi all,
>>
>>First, what I'm running Reiser on:
>>
>>Supermicro dual Xeon motherboard with 2x2.6Ghz xeons in hyperthreaded
>>mode. 3ware 7500-8 (or whatever the call the 8 port ATA card) with 8x250GB
>>disks attatched. 4GB RAM. 
>>
>>Software: 
>>RedHat 9 with latest up2date
>>Kernel 2.4.22 no patches
>>The journal is not on a separate set of spindles.
>>
>>/proc/sys/vm/max-readahead=512
>>/proc/sys/vm/min-readahead=128
>>/proc/sys/vm/bdflush
>>100     5000    640     2560    150     30000   60      20      0
>>
>>Okay. Now for the issue at hand. When the logical disk is being read from,
>>reiser is fast and effecient. We have millions (10M?) of files (about 1M
>>each) in thousands of directories. Reiser reads well (exporting the disk
>>over NFS) and we're very impressed by it. It's a bit slow on the writes
>>and the system load goes up marginally, but that's not a big deal. The
>>thing that puzzles me is that when we perform functions like "find" or in
>>perl "-e filename" or anything that uses fstat() or stat64() or any of
>>those functions brings the system usage to 100% and the load climbs
>>quickly. 
>>
>>Are there any patches, kernel updates, tuning, etc that can help with this
>>problem?
>>    
>>
>
>You could boot with profile=2 and send the results of a readprofile
>command taken after the system load goes very high.  This will slow down
>your box for general usage, so you would only want to run with profile=2
>for a short time.
>
>My guess is the stats are being done across a large directory tree and
>this is generating lots of atime updates.  You could mount -o
>noatime,nodiratime, which will reduce the amount of work reiserfs does
>on each stat.
>
>atimes are used by many mail programs to find out the last time you read
>your mailbox file.  nodiratime probably won't affect most applications.
>
>-chris
>
>
>
>
>  
>
profiling will also tell you if the performance problem is in user 
space.....;-)

-- 
Hans