[dpdk-dev] Having troubles binding an SR-IOV VF to uio_pci_generic on Amazon instance
Alexander Duyck
alexander.duyck at gmail.com
Thu Oct 1 23:17:49 CEST 2015
On 10/01/2015 02:42 AM, Michael S. Tsirkin wrote:
> On Thu, Oct 01, 2015 at 12:22:46PM +0300, Avi Kivity wrote:
>> even when they are some users
>> prefer to avoid the performance penalty.
> I don't think there's a measureable penalty from passing through the
> IOMMU, as long as mappings are mostly static (i.e. iommu=pt). I sure
> never saw any numbers that show such.
It depends on the IOMMU. I believe Intel had a performance penalty on
all CPUs prior to Ivy Bridge. Since then things have improved to where
they are comparable to bare metal.
The graph on page 5 of
https://networkbuilders.intel.com/docs/Network_Builders_RA_vBRAS_Final.pdf
shows the penalty clear as day. Pretty much anything before Ivy Bridge
w/ small packets is slowed to a crawl with an IOMMU enabled.
- Alex
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