[ovs-dev] [PATCH] Improve MPLSoGRE performance by reducing EMC hash collisions.

Ilya Maximets i.maximets at samsung.com
Wed Aug 14 08:12:23 UTC 2019

On 13.08.2019 20:49, Nitin Katiyar wrote:
> When a packet is received, the RSS hash is calculated if it is not
> already available. The Exact Match Cache (EMC) entry is then looked up
> using this RSS hash.
> When a MPLSoGRE encapsulated packet is received, the GRE header is
> popped, the RSS hash is invalidated and the packet is recirculated for
> further processing. When the recirculated packet is processed, the MPLS
> header is popped and the packet is recirculated again. Since the RSS
> hash has not been invalidated here, the EMC lookup will hit the same
> entry as that after the first recirculation. This degrades performance
> severely.

Hmm. Function 'dpif_netdev_packet_get_rss_hash()' accounts recirculation
depth into the hash to avoid such cases. Why this doesn't work for you?

Best regards, Ilya Maximets.

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