On Wed, Jul 24, 2019 at 03:25:07PM +0100, John Garry wrote: > On 24/07/2019 13:20, Will Deacon wrote: > > On Wed, Jul 24, 2019 at 10:58:26AM +0100, John Garry wrote: > > > On 11/07/2019 18:19, Will Deacon wrote: > > > > This is a significant rework of the RFC I previously posted here: > > > > > > > > https://lkml.kernel.org/r/20190611134603.4253-1-will.dea...@arm.com > > > > > > > > But this time, it looks like it might actually be worthwhile according > > > > to my perf profiles, where __iommu_unmap() falls a long way down the > > > > profile for a multi-threaded netperf run. I'm still relying on others to > > > > confirm this is useful, however. > > > > > > > > Some of the changes since last time are: > > > > > > > > * Support for constructing and submitting a list of commands in the > > > > driver > > > > > > > > * Numerous changes to the IOMMU and io-pgtable APIs so that we can > > > > submit commands in batches > > > > > > > > * Removal of cmpxchg() from cmdq_shared_lock() fast-path > > > > > > > > * Code restructuring and cleanups > > > > > > > > This current applies against my iommu/devel branch that Joerg has pulled > > > > for 5.3. If you want to test it out, I've put everything here: > > > > > > > > > > > > https://git.kernel.org/pub/scm/linux/kernel/git/will/linux.git/log/?h=iommu/cmdq > > > > > > > > Feedback welcome. I appreciate that we're in the merge window, but I > > > > wanted to get this on the list for people to look at as an RFC. > > > > > > > > > > I tested storage performance on this series, which I think is a better > > > scenario to test than network performance, that being generally limited by > > > the network link speed. > > > > Interesting, thanks for sharing. Do you also see a similar drop in CPU time > > to the one reported by Ganapat? > > Not really, CPU load reported by fio is mostly the same.
That's a pity. Maybe the cmdq isn't actually getting hit very heavily by fio. > > > Baseline performance (will/iommu/devel, commit 9e6ea59f3) > > > 8x SAS disks D05 839K IOPS > > > 1x NVMe D05 454K IOPS > > > 1x NVMe D06 442k IOPS > > > > > > Patchset performance (will/iommu/cmdq) > > > 8x SAS disk D05 835K IOPS > > > 1x NVMe D05 472K IOPS > > > 1x NVMe D06 459k IOPS > > > > > > So we see a bit of an NVMe boost, but about the same for 8x disks. No > > > iommu > > > performance is about 918K IOPs for 8x disks, so it is not limited by the > > > medium. > > > > It would be nice to know if this performance gap is because of Linux, or > > simply because of the translation overhead in the SMMU hardware. Are you > > able to get a perf profile to see where we're spending time? > > I'll look to do that, but I'd really expect it to be down to the time linux > spends on the DMA map and unmaps. Right, and it would be good to see how much of that is in SMMUv3-specific code. Another interesting thing to try would be reducing the depth of the io-pgtable. We currently key that off VA_BITS which may be much larger than you need (by virtue of being a compile-time value). Will _______________________________________________ iommu mailing list iommu@lists.linux-foundation.org https://lists.linuxfoundation.org/mailman/listinfo/iommu
