Re: per-cpu blk_plug_list

[Jesse Barnes]

On Mon, Mar 01, 2004 at 01:18:40PM -0800, Chen, Kenneth W wrote:
> blk_plug_list/blk_plug_lock manages plug/unplug action.  When you have
> lots of cpu simultaneously submits I/O, there are lots of movement with
> the device queue on and off that global list.  Our measurement showed
> that blk_plug_lock contention prevents linux-2.6.3 kernel to scale pass
> beyond 40 thousand I/O per second in the I/O submit path.

This helped out our machines quite a bit too.  Without the patch, we
weren't able to scale above 80000 IOPS, but now we exceed 110000 (and
parity with our internal XSCSI based tree).

Maybe the plug lists and locks should be per-device though, rather than
per-cpu?  That would make the migration case easier I think.  Is that
possible?

Thanks,
Jesse
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