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 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.

Then  I tried playing with these settings and set

/proc/sys/kernel/sched_rt_runtime_us to   95000
/proc/sys/kernel/sched_rt_period_us    to 100000

And even with  the switch from sirq-net-rx to idle happens every seconds 
and stays in idle for 0.05 seconds.  Are they any restrictions on what 
these can be set to? I guess these setting may not be reasonable. I did 
verify by doing a cat of these files and read back the expected values.

Then I tried

/proc/sys/kernel/sched_rt_period_us     to 1000000
/proc/sys/kernel/sched_rt_runtime_us   to 980000

Even here the idle is for 0.05 seconds

> Best regards
> Uwe
>

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