Re: [PATCH 4/4] MSR: msr Batch processing feature

Andy Lutomirski
2016-02-26T02:48:57Z

On Thu, Feb 25, 2016 at 4:02 PM, Marty McFadden <mcfadden8@llnl.gov> wrote:
> Provides a new ioctl interface through /dev/cpu/msr_batch.
>
> This implementation will cause an Inter Processor Interrupt to be sent
> to each destination processor and will wait until all processors have
> finished processing their respective batch of MSR operations before
> returning.

This comes up periodicially, and it needs to be benchmarked against
the sane way to do it in userspace:

For each CPU: sched_setaffinity to bind to that CPU, and then a bunch
of conventional MSR accesses. Optionally do all the CPUs at once
using lots of threads.

Please do this benchmark on a kernel that is *not* using nohz_full.
The nohz_full implementaion in current kernels has abysmal syscall
performance, but that's improving rapidly.

--Andy