Re: [9fans] 9front pegs CPU on VMware

[erik quanstrom <quanstro@labs.coraid.com>]

> /*
>  *  put the processor in the halt state if we've no processes to run.
>  *  an interrupt will get us going again.
>  */
> void
> idlehands(void)
> {
>         extern int nrdy;
>
>         if(conf.nmach == 1)
>                 halt();
>         else if(m->cpuidcx & Monitor)
>                 mwait(&nrdy);
> }
>
> the reason for not just unconditionally calling halt() on a
> *multiprocessor*
> is that this would keep the processor sleeping even when processes become
> ready to be executed. there is currently no way for the first woken
> processor
> to wakup another one other than the monitor/mwait mechanism; which for some
> reason seems not to be emulated in that vmware fusion setup. one can run
> aux/cpuid to see what processor features are supported.
>
> yes, theres the HZ tick that should wake up the sleeping processor
> eventually,
> but then it might be too late.

it won't be "too late"—as causing failures.  i've tried testing this and
generally found that reduced contention on the dog pile lock means
unconditionally halting gives a performance boost.

- erik