Re: [PATCH RFC 0/2] Optimize the snmp stat aggregation for large cpus

From: Raghavendra K T
Date: Tue Aug 25 2015 - 11:58:58 EST

On 08/25/2015 08:03 PM, Eric Dumazet wrote:
On Tue, 2015-08-25 at 13:24 +0530, Raghavendra K T wrote:
While creating 1000 containers, perf is showing lot of time spent in
snmp_fold_field on a large cpu system.

The current patch tries to improve by reordering the statistics gathering.

Please note that similar overhead was also reported while creating
veth pairs

160 cpu (20 core) baremetal powerpc system with 1TB memory

I wonder if these kind of results would demonstrate cache coloring
problems on this host. Looks like all the per cpu data are colliding on
same cache lines.

It could be. My testing on a 128 cpu system with less memory did not
incur huge time penalty for 1000 containers.
But snmp_fold_field in general had the problem.
for e.g. same experiment I had around 15% overhead for snmp_fold reduced to 5% after the patch.

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