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Date: Tue, 10 Aug 2021 10:36:47 +0100 From: John Garry <john.garry@...wei.com> To: Ming Lei <ming.lei@...hat.com> CC: Robin Murphy <robin.murphy@....com>, <linux-kernel@...r.kernel.org>, <linux-nvme@...ts.infradead.org>, <iommu@...ts.linux-foundation.org>, "Will Deacon" <will@...nel.org>, <linux-arm-kernel@...ts.infradead.org> Subject: Re: [bug report] iommu_dma_unmap_sg() is very slow then running IO from remote numa node On 28/07/2021 16:17, Ming Lei wrote: >>>> Have you tried turning off the IOMMU to ensure that this is really just >>>> 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). >>> Bypassing SMMU via iommu.passthrough=1 basically doesn't make a difference >>> on this issue. >> A ~90% throughput drop still seems to me to be too high to be a software >> issue. More so since I don't see similar on my system. And that throughput >> drop does not lead to a total CPU usage drop, from the fio log. >> >> Do you know if anyone has run memory benchmark tests on this board to find >> out NUMA effect? I think lmbench or stream could be used for this. > https://lore.kernel.org/lkml/YOhbc5C47IzC893B@T590/ Hi Ming, Out of curiosity, did you investigate this topic any further? And you also asked about my results earlier: On 22/07/2021 16:54, Ming Lei wrote: >> [ 52.035895] nvme 0000:81:00.0: Adding to iommu group 5 >> [ 52.047732] nvme nvme0: pci function 0000:81:00.0 >> [ 52.067216] nvme nvme0: 22/0/2 default/read/poll queues >> [ 52.087318] nvme0n1: p1 >> >> So I get these results: >> cpu0 335K >> cpu32 346K >> cpu64 300K >> cpu96 300K >> >> So still not massive changes. > In your last email, the results are the following with irq mode io_uring: > > cpu0 497K > cpu4 307K > cpu32 566K > cpu64 488K > cpu96 508K > > So looks you get much worse result with real io_polling? > Would the expectation be that at least I get the same performance with io_polling here? Anything else to try which you can suggest to investigate this lower performance? Thanks, John
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