RE: [Xen-devel] 2.4.29-xenU VBD performance (problem)

["Ian Pratt" <m+Ian.Pratt@xxxxxxxxxxxx>]

> I enabled hyperthreading and ran dom0 with cpu0 and domU with cpu1.
> 
> dom0 performance remained the same as previously (93 MB/sec).
> 
> 2.6.10-xenU performance increased from 58 MB/sec -> 69 MB/sec.
> 2.4.29-xenU performance remained the same at 23 MB/sec.
> 
> It seems that enabling hyperthreading and running domains 
> with different
> (virtual) cpu:s increase performance.

It's possible that what is happening heere is that the the MAX_PENDING_REQS is 
too small for your system with multiple disks in a s/w raid-5.

Increasing this value is going to require us to do a little bit of work (as the 
ring buffer will no longer fit in a page). However, it would be instructive if 
you could *reduce* this by e.g. 10% and see how if effects performance. If the 
answer is "it goes to hell" then that's a good sign that it'll be worth our 
effort increasing it. 
 
> It might be.. anyway, 2.4-domU performance is really bad..

The 2.4 blkfront code is very old and probably needs a spring clean -- all the 
effort has gone into 2.6 recently. Perhaps someone will volunteer to take a 
look?

Ian


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