RE: Regression with SLUB on Netperf and Volanomark

[Chen, Tim C]

Christoph Lameter wrote:
> Try to boot with
> 
> slub_max_order=4 slub_min_objects=8
> 
> If that does not help increase slub_min_objects to 16.
> 

We are still seeing a 5% regression on TCP streaming with
slub_min_objects set at 16 and a 10% regression for Volanomark, after
increasing slub_min_objects to 16 and setting slub_max_order=4 and using
the 2.6.21-rc7-mm2 kernel.  The performance between slub_min_objects=8
and 16 are similar.

>> We found that for Netperf's TCP streaming tests in a loop back mode,
>> the TCP streaming performance is about 7% worse when SLUB is enabled
>> on 
>> 2.6.21-rc7-mm1 kernel (x86_64).  This test have a lot of sk_buff
>> allocation/deallocation.
> 
> 2.6.21-rc7-mm2 contains some performance fixes that may or may not be
> useful to you.

We've switched to 2.6.21-rc7-mm2 in our tests now.

>> 
>> For Volanomark, the performance is 7% worse for Woodcrest and 12%
>> worse for Clovertown.
> 
> SLUBs "queueing" is restricted to the number of objects that fit in
> page order slab. SLAB can queue more objects since it has true queues.
> Increasing the page size that SLUB uses may fix the problem but then
> we run into higher page order issues.
> 
> Check slabinfo output for the network slabs and see what order is
> used. The number of objects per slab is important for performance.

The order used is 0 for the buffer_head, which is the most used object.

I think they are 104 bytes per object.

Tim
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