Re: [PATCH 0/4] iommu/arm-smmu-v3: Improve cmdq lock efficiency

Will Deacon
2020-07-16T10:22:40Z

On Thu, Jul 16, 2020 at 11:19:41AM +0100, Will Deacon wrote:
> On Tue, Jun 23, 2020 at 01:28:36AM +0800, John Garry wrote:
> > As mentioned in [0], the CPU may consume many cycles processing
> > arm_smmu_cmdq_issue_cmdlist(). One issue we find is the cmpxchg() loop to
> > get space on the queue takes approx 25% of the cycles for this function.
> >
> > This series removes that cmpxchg().
>
> How about something much simpler like the diff below?

Ah, scratch that, I don't drop the lock if we fail the cas with it held.
Let me hack it some more (I have no hardware so I can only build-test this).

Will