On Mon, Jul 26, 2021 at 3:51 PM John Garry<john.garry@xxxxxxxxxx> wrote:
On 23/07/2021 11:21, Ming Lei wrote:Bypassing SMMU via iommu.passthrough=1 basically doesn't make a difference
Have you tried turning off the IOMMU to ensure that this is really justThanks, I was also going to suggest the latter, since it's whatThe improvement from 'iommu.strict=0' is very small:
arm_smmu_cmdq_issue_cmdlist() does with IRQs masked that should be most
indicative of where the slowness most likely stems from.
an IOMMU problem?
You can try setting CONFIG_ARM_SMMU_V3=n in the defconfig or passing
cmdline param iommu.passthrough=1 to bypass the the SMMU (equivalent to
disabling for kernel drivers).
on this issue.
And from fio log, submission latency is good, but completion latency
is pretty bad,
and maybe it is something that writing to PCI memory isn't committed to HW in