Custom Linux Kernel Scheduler issue

Greg KH greg at
Thu Nov 24 02:18:50 EST 2016

On Thu, Nov 24, 2016 at 02:01:41AM -0500, Kenneth Adam Miller wrote:
> Hello,
> I have a scheduler issue in two different respects:
> 1) I have a process that is supposed to tight loop, and it is being
> given very very little time on the system. I don't want that - I want
> those who would use the processor to be given the resources to run as
> fast as they each can.

What is causing it to give up its timeslice?  Is it waiting for I/O?
Doing something else to sleep?

> 2) I am seeing with perf that the maximum overhead at each section
> does not sum up to be more than 15 percent. Total, probably something
> like 18% of cpu time is used, and my binary has rocketed in slowness
> from about 2 seconds or less total to several minutes.

What changed to make things slower?  Did you change kernel versions or
did you change something in your userspace program?

> I think that
> the linux scheduler isn't scheduling it, because this process is just
> some unit tests that double as benchmarks in that they shm_open a file
> and write into it with memcpy's.

Are you sure that I/O isn't happening here like through swap or
something else?

What does perf say is taking all of your time?


greg k-h

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