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

[Venkat Subbiah <vsubbiah@caviumnetworks.com>]

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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