On Wed, Jul 24, 2019 at 03:03:20PM +0100, John Garry wrote: > On 24/07/2019 13:15, Will Deacon wrote: > > > Could it be a minor optimisation to advance the HW producer pointer at > > > this > > > stage for the owner only? We know that its entries are written, and it > > > should be first in the new batch of commands (right?), so we could advance > > > the pointer to at least get the HW started. > > > > I think that would be a valid thing to do, but it depends on the relative > > cost of writing to prod compared to how long we're likely to wait. Given > > that everybody has irqs disabled when writing out their commands, I wouldn't > > expect the waiting to be a big issue, > > For sure, but I'm thinking of the possible scenario where the the guy(s) > we're waiting on have many more commands. Or they just joined the current > gathering quite late, just prior to clearing the owner flag.
Understood, but a "cacheable" memcpy (assuming the SMMU is coherent) should be pretty quick, even for maximum batch size I think. > although we could probably optimise > > arm_smmu_cmdq_write_entries() into a memcpy() if we needed to. > > > > In other words, I think we need numbers to justify that change. > > Anyway, this is quite minor, and I will see if the change could be justified > by numbers. Thanks! If the numbers show it's useful, we can definitely add it. Will _______________________________________________ iommu mailing list [email protected] https://lists.linuxfoundation.org/mailman/listinfo/iommu
