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Re: task switch from net-rx to idle when there is napi processing to be done

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On 01/26/2012 07:29 AM, Steven Rostedt wrote:
On Wed, 2012-01-25 at 03:30 -0800, Venkat Subbiah wrote:
On 01/25/2012 12:55 AM, Uwe Kleine-König wrote:
Hello,

On Tue, Jan 24, 2012 at 06:39:34PM -0800, Venkat Subbiah wrote:
In the process of debugging a napi ethernet driver performance
issue, what I am noticing is

1. While the driver is in the middle of a napi packet processing
loop, there is a task switch from
sirq-net-rx to idle even though there is pending napi processing to be done.
I didn't check your logs below, but maybe this is related to the default
settings in /proc/sys/kernel/sched_rt_period_us and
/proc/sys/kernel/sched_rt_runtime_us? That is 0.05s per second is
reserved for non-RT tasks tasks such that a run-away realtime process
will not lock up the machine.

To verify that, try

	echo -1>   /proc/sys/kernel/sched_rt_runtime_us

.
Thanks for you response. That was it. Setting this to -1 does the expected.
Note, you should also have seen a warning in the logs when an RT task is
throttled. Did you see such a thing?
I didn't get to the console,but it is in the kernel logs.

-- Steve




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