Re: [PATCH v2 net-next] tcp: avoid expensive pskb_expand_head() calls

Eric Dumazet
2012-04-19T14:10:57Z

On Thu, 2012-04-19 at 15:52 +0200, Eric Dumazet wrote:

> And disabling GRO on receiver definitely demonstrates the problem, even
> with a single flow. (and performance drops from 9410 Mbit to 6050 Mbit)

That insane.

Performance drops so much because we _drop_ incoming ACKS :

< TCPSackShifted: 39117
< TCPSackMerged: 16500
< TCPSackShiftFallback: 5092
< TCPBacklogDrop: 27965
---
> TCPSackShifted: 35122
> TCPSackMerged: 16368
> TCPSackShiftFallback: 4889
> TCPBacklogDrop: 23247

Hmm, maybe we should reduce skb->truesize for small packets before
queueing them in socket backlog...