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[Xen-users] Bad TCP accept performance

To: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: [Xen-users] Bad TCP accept performance
From: Carl Byström <cgbystrom@xxxxxxxxx>
Date: Mon, 23 May 2011 18:31:01 +0200
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I've been running some simple tests trying to find out why the TCP accept() rate has been so low on my Xen guest.
The rate at which I can accept new TCP connections is about five times better on a bare metal machine compared to my guest.
Been using netperf with the TCP_CRR test to simulate this behavior.

I originally posted this question at Server Fault (http://serverfault.com/questions/272483/why-is-tcp-accept-performance-so-bad-under-xen) along with lots of more details how I have performed these tests.
After a suggestion from a user there, I decided to try this list. Judging from the number of views the questions did receive at Server Fault and being top-3 voted at Hacker News, I presume this issue is something a lot of users care about.
One user at HN also reported that this apparently is a known issue and is due to small packet performance, affecting both Xen and KVM.

After collecting feedback from SF and HN users, my question is: what can you do to improve small packet performance in Xen?
Is this a fundamentally difficult problem to solve with Xen or is there a "quick fix"?


Carl Byström
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