On Thu, Jan 24, 2019 at 12:10 AM Nadav Har'El <[email protected]> wrote:
> On Wed, Dec 19, 2018 at 2:26 PM Waldemar Kozaczuk <[email protected]> > wrote: > >> This patch adds "emms" instruction in critical places >> > > Thank you so much for working on this, and sorry for having delayed my > review for SO long. > I'm basically happy with this patch except one thing that nags me - I > don't understand why the > *second* EMMS call, the one in switch_to(), is necessary. And I'd really > like to understand. > I have a *guess* below why it might be necessary, and I would be really > grateful if you could > check my guess. I also have a couple of other small comments below. > > By the way, I checked whether these new EMMS calls have any performance penalty for context switches (especially voluntary ones, which are supposed to be faster) by using tests/misc-ctxsw.so, and I was pleasantly surprised that there wasn't any measureable difference! On my machine, the single-CPU ("colocated") voluntary context switch time measured in this test was around 400 nanoseconds, with about 8 nanoseconds variations, but various estimates I read on the web suggest EMMS latency is between 1-2 nanoseconds, so it is very much below my noise level, and therefore negligible. Which is great news. Nadav. -- You received this message because you are subscribed to the Google Groups "OSv Development" group. To unsubscribe from this group and stop receiving emails from it, send an email to [email protected]. For more options, visit https://groups.google.com/d/optout.
