Re: [PATCH v3 00/11] PCID and improved laziness

[Andy Lutomirski]

On Wed, Jun 21, 2017 at 11:23 AM, Linus Torvalds
<torvalds@xxxxxxxxxxxxxxxxxxxx> wrote:
> On Tue, Jun 20, 2017 at 10:22 PM, Andy Lutomirski <luto@xxxxxxxxxx> wrote:
>> There are three performance benefits here:
>
> Side note: can you post the actual performance numbers, even if only
> from some silly test program on just one platform? Things like lmbench
> pipe benchmark or something?
>
> Or maybe you did, and I just missed it. But when talking about
> performance, I'd really like to always see some actual numbers.

Here are some timings using KVM:

pingpong between two processes using eventfd:
patched: 883ns
unpatched: 1046ns (with considerably higher variance)

madvise(MADV_DONTNEED); write to the page; switch CPUs:
patched: ~12.5us
unpatched: 19us

The latter test is a somewhat contrived example to show off the
improved laziness.  Current kernels send an IPI on each iteration if
the system is otherwise idle.