Messages in this thread | | | From | Bernd Schubert <> | Subject | Re: deadline unfairness | Date | Mon, 24 Mar 2008 17:44:35 +0100 |
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Hallo Aron,
On Saturday 22 March 2008, Bernd Schubert wrote: > Hello Aron, > > On Saturday 22 March 2008, Aaron Carroll wrote: > > Bernd Schubert wrote: > > > Hello, > > > > > > some it seems the deadline scheduler is rather unfair. Below is an > > > example of md-raid6 initialization of md3, md4 and md5. All three > > > md-devices do share the same blockdevices (we have patched md to allow > > > parallel rebuild of shared block devices, since for us the cpu is the > > > bottleneck and not the block device). > > > > > > All rebuilds started basically at the same time, as you can see, md3 is > > > already done and now md4 rebuilds substantially faster than md5. > > > [..] > > > This is basically with a 2.6.22 kernel + lustre + md-backports, but > > > nothing done to the scheduler. > > > > Hi Bernd, > > > > There is a deadline bug in pre-2.6.24 kernels where lower-sector requests > > can starve higher-sector requests; you might be hitting this bug. It was > > fixed by commit: 6f5d8aa6382eef2b26032c88656270bdae7f0c42 > > thanks a lot for your help! I will build a new kernel later on today and > then report back if it helps. Commit > dfb3d72a9aa519672c9ae06f0d2f93eccb35482f also looks useful...
After applying both patches it looks much better now.
Thanks again for your help, Bernd
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