[Pvfs2-developers] help debugging request processor/distribution

[Rob Ross]

if the processes were working on different files it is likely because 
the resulting i/o pattern is more sequential.

Murali Vilayannur wrote:
> Hi Phil,
> 
>> I did find one odd result, although it is somewhat unrelated.  In an
>> earlier email on this topic I mentioned that I was able to find a
>> temporary workaround for the bug by setting PVFS2_BUFMAP_DESC_COUNT to
>> 1, which limits pvfs2-client-core to only performing one I/O operation
>> at a time.  A surprising side effect of this was that (regardless of the
>> flow post order) this configuration substantially increased performance
>> for a 5 process I/O benchmark.
>>
>> In this particular test there are 5 processes, each both reading and
>> writing large files on the same PVFS2 file system.  The results are
>> counter-intuitive, because the whole point of having multiple buffers
>> was to allow more concurrent activity when multiple processes perform
>> I/O.  However, the test went faster when only one I/O operation was
>> allowed to proceed at a time.
> 
> Wow.. That is interesting indeed. I will see if I can trigger this
> behavior as well..Thanks for the info!
> Murali
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