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

[Venkat Subbiah <vsubbiah@caviumnetworks.com>]

On 01/25/2012 01:18 AM, Mike Galbraith wrote:
> On Wed, 2012-01-25 at 09:55 +0100, 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
> Hm, makes sense if this is a UP box.  SMP would just go borrow a cup of
> runtime from a neighbor.
Yes this experiment was when running with only one core.
> 	-Mike
>
>

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