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[Xen-devel] Xen network performance degradation with a net-front commit


I'm observing a huge performance drop for memcached workload on x86
with the following commit, which was merged to Linux kernel 4.5.
Before this patch, memcached overhead is about 113% (i.e. 13% slower
than native Linux) [1], but with this patch it becomes 175%. I
observed even bigger performance drop on other hardware platforms.

commit 7d0105b5334b9722b7d33acad613096dfcf3330e
Author: Malcolm Crossley <malcolm.crossley@xxxxxxxxxx>
Date:   Tue Jan 26 17:12:44 2016 +0000

    xen-netfront: request Tx response events more often

I'm comparing performance between Linux kernel 4.0 and 4.15 in DomU,
and I'm seeing this behavior both with Xen 4.5.0 and Xen 4.10.1. I'm
using 4vcpus for Dom0 and pvhvm DomU.

I wonder in what scenario this patch helps to improve performance and
doesn't? I also wonder if others observed a similar behavior?


[1] http://www.cs.columbia.edu/~cdall/pubs/isca2016-dall.pdf

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