Re: 2.5.38-mm3

On Fri, Sep 27, 2002 at 08:04:31AM -0700, Martin J. Bligh wrote:

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What application were you all running ?

Kernel compile on NUMA-Q looks like this:

125673 total
82183 default_idle
2288 d_lookup
1921 vm_enough_memory
1883 __generic_copy_from_user
1566 file_read_actor
1381 .text.lock.file_table           <-------------

More likely, this is contention for the files_lock. Do you have any 
lockmeter data ?  That should give us more information. If so,
the files_struct_rcu isn't likely to help.

1168 find_get_page
1116 get_empty_filp

Presumably that's the same thing? Interestingly, if I look back at 
previous results, I see it's about twice the cost in -mm as it is 
in mainline, not sure why ... at least against 2.5.37 virgin it was.

Not sure why it shows up more in -mm, but likely because -mm has
lot less contention on other locks like dcache_lock.

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Please try running the files_struct_rcu patch where fget() is lockfree
and let me know what you see.

Will do ... if you tell me where it is ;-)

Oh, the usual place -
http://sourceforge.net/project/showfiles.php?group_id=8875&release_id=112473
I wish sourceforge FRS continued to allow direct links to patches.

Thanks
-- 
Dipankar Sarma  [off-list ref] http://lse.sourceforge.net
Linux Technology Center, IBM Software Lab, Bangalore, India.
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On Fri, Sep 27, 2002 at 10:44:24PM +0530, Dipankar Sarma wrote:

Not sure why it shows up more in -mm, but likely because -mm has
lot less contention on other locks like dcache_lock.

Well, the profile I posted was an interactive UP workload, and it's
fairly high there. Trimming cycles off this is good for everyone.

Small SMP boxen (dual?) used similarly will probably see additional
gains as the number of locked operations in fget() will be reduced.
There's clearly no contention or cacheline bouncing in my workloads as
none of them have tasks sharing file tables, nor is anything else
messing with the cachelines.


Cheers,
Bill
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