On Wed, 2015-11-25 at 15:46 +0100, jroe...@suse.de wrote: > On Tue, Nov 24, 2015 at 02:05:12PM -0800, Shaohua Li wrote: > > The lib/iommu-common.c uses a bitmap and a lock. This implementation > > actually uses a percpu_ida which completely avoids locking. It would be > > possible to make lib/iommu-common.c use percpu_ida too if somebody wants > > to do it, but I think this shouldn't be a blocker for these patches > > giving it has huge performance gain. > > It doesn't "completely avoids locking", the percpu_ida code uses a lock > internally too. Also, what is the memory and device address space > overhead per cpu?
A percpu lock doesn't bounce cachelines between CPUs very much, so from
that point of view it might as well not exist :)
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David Woodhouse Open Source Technology Centre
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