linux-kernel - Re: Poor UDP performance using 2.6.21-rc5-rt5

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Date:	Mon, 2 Apr 2007 11:37:40 +0200
From:	Ingo Molnar <mingo@...e.hu>
To:	Dave Sperry <dave_sperry@...e.org>
Cc:	linux-rt-users@...r.kernel.org, linux-kernel@...r.kernel.org
Subject: Re: Poor UDP performance using 2.6.21-rc5-rt5


* Dave Sperry <dave_sperry@...e.org> wrote:

> I checked the clock source and in both the vanilla and rt cases and 
> they were both acpi_pm

ok, thanks for double-checking that.

> Here's the oprofile for my vanilla case:

i tried your workload and i think i managed to optimize it some more: i 
have uploaded the -rt8 kernel with these improvements included - could 
you try it? Is there any measurable improvement relative to -rt5?

one more thing to improve netperf performance is to do this before 
running it:

  chrt -f -p 50 $$

this will put netperf on the same priority level as the net hardirq and 
the net softirq (which both default to SCHED_FIFO:50), and should result 
in a (much) reduced context-switch rate.

Or, if networking is not latency-critical, then you could move the net 
hardirq and softirq threads to SCHED_BATCH, and run netperf under 
SCHED_BATCH as well, using:

  chrt -b -p 0 $$

and figuring out the active softirq hardirq thread PIDs and "chrt -b" 
-ing them too.

	Ingo
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