Re: scsi-mq V2

[Benjamin LaHaise]

On Wed, Jul 09, 2014 at 11:20:40PM -0700, Christoph Hellwig wrote:
> On Thu, Jul 10, 2014 at 12:53:36AM +0000, Elliott, Robert (Server Storage) wrote:
> > the problem still occurs - fio results in low or 0 IOPS, with perf top 
> > reporting unusual amounts of time spent in do_io_submit and io_submit.
> 
> The diff between the two version doesn't show too much other possible
> interesting commits, the most interesting being some minor block
> updates.
> 
> I guess we'll have to a manual bisect, I've pushed out a
> scsi-mq.3-bisect-1 branch that is rebased to just before the merge of
> the block tree, and a scsi-mq.3-bisect-2 branch that is just after
> the merge of the block tree to get started.

There is one possible concern that could be exacerbated by other changes in 
the system: if the application is running close to the bare minimum number 
of requests allocated in io_setup(), the per cpu reference counters will 
have a hard time batching things.  It might be worth testing with an 
increased number of requests being allocated if this is the case.

		-ben
-- 
"Thought is the essence of where you are now."
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