On Wed, Nov 25, 2015 at 09:43:49AM -0700, Jens Axboe wrote: > On 11/25/2015 09:40 AM, Woodhouse, David wrote: > >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 :) > > As long as the address space can remain more than ~50% empty, it is > indeed practically lockless. Are we ever worried about higher > utilization? If so, in my experience percpu_ida fails miserable near > or at exhaustion.
The patch uses TASK_RUNNING for tag allocation, so it doesn't wait. I thought it's ok, no? Thanks, Shaohua _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
