[Date Prev][Date Next][Thread Prev][Thread Next][Date Index][Thread Index] Re: [Xen-devel] poor domU VBD performance.
On Monday 28 March 2005 14:14, Ian Pratt wrote: > > > > > I found out that dom0 does file-system IO and raw IO ( using > > > > > dd as a tool to test > > > > > throughput from the disk ) is about exactly the same as when > > > > > using a standard > > > > > linux kernel without XEN. But the raw IO from DomU to an > > > > > unused disk ( a second > > > > > disk in the system ) is limited to fourty percent of the > > > > > speed I get within Dom0. > > > > Is the second disk exactly the same as the first one? I'll > > try an IO test > > here on the same disk array with dom0 and domU and see what I get. > > I've reproduced the problem and its a real issue. > > It only affects reads, and is almost certainly down to how the blkback > driver passes requests down to the actual device. > > Does anyone on the list actually understand the changes made to linux > block IO between 2.4 and 2.6? > > In the 2.6 blkfront there is no run_task_queue() to flush requests to > the lower layer, and we use submit_bio() instead of 2.4's > generic_make_request(). It looks like this is happening syncronously > rather than queueing multiple requests. What should we be doing to cause > things to be batched? There are multiple IO schedulers in 2.6. Do you know which one is being used? It should say somewhere in the boot log. Some read-ahead code also changed in 2.6.10-11 range. So far I have not been able to reproduce this in xen-unstable with 2.6. I am building xen-2.0.5 for a look. -Andrew _______________________________________________ Xen-devel mailing list Xen-devel@xxxxxxxxxxxxxxxxxxx http://lists.xensource.com/xen-devel
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