On 05/02/2013 10:13 AM, Yan Burman wrote:
-----Original Message-----
From: Michael S. Tsirkin [mailto:[email protected]]
Sent: Thursday, May 02, 2013 04:56
To: Or Gerlitz
Cc: Roland Dreier; [email protected]; Yan Burman; linux-
[email protected]
Subject: Re: decent performance drop for SCSI LLD / SAN initiator when
iommu is turned on
On Thu, May 02, 2013 at 02:11:15AM +0300, Or Gerlitz wrote:
Hi Roland, IOMMU folks,
So we've noted that when configuring the kernel&& booting with intel
iommu set to on on a physical node (non VM, and without enabling SRIOV
by the HW device driver) raw performance of the iSER (iSCSI RDMA) SAN
initiator is reduced notably, e.g in the testbed we looked today we
had ~260K 1KB random IOPS and 5.5GBs BW for 128KB IOs with iommu
turned off for single LUN, and ~150K IOPS and 4GBs BW with iommu
turned on. No change on the target node between runs.
That's why we have iommu=pt.
See definition of iommu_pass_through in arch/x86/kernel/pci-dma.c.
I tried passing "intel_iommu=on iommu=pt" to 3.8.11 kernel and I still get
performance degradation.
I get the same numbers with iommu=pt as without it.
I wanted to send perf output, but currently I seem to have some problem with
its output.
Will try to get perf differences next week.
Yan
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dmesg dump? -- interested to see if x2apic is on, and if MSI is used (or not)
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