Re: [PATCH v3 0/7] x86: Rewrite switch_to()

[Ingo Molnar]

* Brian Gerst <brgerst@xxxxxxxxx> wrote:

> On Sat, Aug 13, 2016 at 1:16 PM, Linus Torvalds
> <torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> > On Sat, Aug 13, 2016 at 9:38 AM, Brian Gerst <brgerst@xxxxxxxxx> wrote:
> >> This patch set simplifies the switch_to() code, by moving the stack switch
> >> code out of line into an asm stub before calling __switch_to().  This ends
> >> up being more readable, and using the C calling convention instead of
> >> clobbering all registers improves code generation.  It also allows newly
> >> forked processes to construct a special stack frame to seamlessly flow
> >> to ret_from_fork, instead of using a test and branch, or an unbalanced
> >> call/ret.
> >
> > Do you have performance numbers? Is it noticeable/measurable?
> 
> How do I measure it?  The perf documentation isn't easy to understand.

Something like this:

  taskset 1 perf stat -a -e '{instructions,cycles}' --repeat 10 perf bench sched pipe

... will give a very good idea about the general impact of these changes on 
context switch overhead.

Thanks,

	Ingo