Re: UDP-U stream performance regression on 32-rc1 kernel

From: Ingo Molnar
Date: Tue Nov 03 2009 - 12:45:49 EST

* Zhang, Yanmin <yanmin_zhang@xxxxxxxxxxxxxxx> wrote:

> On Tue, 2009-11-03 at 11:47 +0800, Alex Shi wrote:
> > We found the UDP-U 1k/4k stream of netperf benchmark have some
> > performance regression from 10% to 20% on our Tulsa and some NHM
> > machines.
> ï perf events shows function find_busiest_group consumes about 4.5% cpu
> time with the patch while it only consumes 0.5% cpu time without the
> patch.
> The communication between netperf client and netserver is very fast.
> When netserver receives a message and there is no new message
> available, it goes to sleep and scheduler calls idle_balance =>
> load_balance_newidle. load_balance_newidle spends too much time and a
> new message arrives quickly before load_balance_newidle ends.
> As the comments in the patch say hackbench benefits from it, I tested
> hackbench on Nehalem and core2 machines. hackbench does benefit from
> it, about 6% on nehalem machines, but doesn't benefit on core2
> machines.

Can you confirm that -tip:

has it fixed (or at least improved)?

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