On Mon, Apr 24, 2017 at 10:35 PM, Will Deacon <will.dea...@arm.com> wrote: > On Mon, Apr 24, 2017 at 10:26:53PM +0530, Sunil Kovvuri wrote: >> On Mon, Apr 24, 2017 at 9:38 PM, Will Deacon <will.dea...@arm.com> wrote: >> > On Mon, Apr 24, 2017 at 05:29:36PM +0530, Geetha sowjanya wrote: >> >> From: Geetha <gak...@cavium.com> >> >> >> >> When large memory is being unmapped, huge no of tlb invalidation cmds are >> >> submitted followed by a SYNC command. This sometimes hits CMD queue full >> >> and >> >> poll on queue drain is being timedout throwing error message 'CMD_SYNC >> >> timeout'. >> >> >> >> Although there is no functional issue, error message confuses user. Hence >> >> increased >> >> poll timeout to 500us >> > >> > Hmm, what are you doing to unmap that much? Is this VFIO teardown? Do you >> > have 7c6d90e2bb1a ("iommu/io-pgtable-arm: Fix iova_to_phys for block >> > entries") applied? >> >> Yes it's VFIO teardown and again yes the above fix is applied. >> But i didn't get how above fix is related. >> TLB invalidation commands are submitted at 'arm_smmu_tlb_inv_range_nosync()' >> and it's a loop over granule size. >> >> 1357 do { >> 1358 arm_smmu_cmdq_issue_cmd(smmu, &cmd); >> 1359 cmd.tlbi.addr += granule; >> 1360 } while (size -= granule); >> >> So if invalidation size is big then huge no of invalidation commands >> will be submitted >> irrespective of fix that you pointed above, right ? > > VFIO has some logic to batch up invalidations, but this didn't work properly > for us without the fix above. However, I guess you have a huge memory range > that's mapped with 2M sections or something, so there are still loads of > entries to invalidate. > > I would much prefer it if VFIO could just teardown the whole address space > so that we could do an invalidate all, but there's a chicken-and-egg problem > with page accounting iirc. >
We can definitely look into this from VFIO perspective but for now I am guessing this patch is fine, as no functionality is being changed. What do you say ? Thanks, Sunil.