On Wed, 06 Jun 2012 19:02:16 -0400
Jung-uk Kim <j...@freebsd.org> wrote:
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> On 2012-06-06 17:58:57 -0400, Andriy Gapon wrote:
> > on 31/05/2012 23:28 Jung-uk Kim said the following:
> >> It is simple but I don't like locking scheduler, binding CPU, and
> >> writing the same MSR, multiple times for each core.
> >
> > Not sure if parse this. The MSR is _written_ /once/ for each
> > core. (BTW, "locking scheduler" is not a completely accurate
> > description of what thread_lock does)
>
> I apologize. I didn't see the whole picture and read your patch
> wrong.
>
> Any way, hwpstate still isn't quite right even without your patch.
>
> sys/kern/kern_cpu.c
> cpufreq_curr_sysctl() ->
> CPUFREQ_SET() -> /* for all CPU devices */
> cf_set_method() -> /* thread_lock(), sched_bind(), ...
> */ CPUFREQ_DRV_SET() ->
> sys/x86/cpufreq/hwpstate.c
> hwpstate_set() ->
> hwpstate_goto_pstate() /* for each CPU unit */
> /* thread_lock(), sched_bind(), ... */
>
> Therefore, "sysctl dev.cpu.0.cpufreq=<freq>" loops n^2 times (i.e., n
> times per CPU) where n is number of CPUs. At least, it should check
> unit == 0, e.g.,
>
> hwpstate_goto_pstate(...)
> {
> ...
> if (unit == 0) {
> /* XXX Is this really necessary? */
> CPU_FOREACH(i) {
> ...
> wrmsr(MSR_AMD_10H_11H_CONTROL, id);
> ...
> }
> }
> /* Check the current P-state. */
> for (...) {
> ...
> msr = rdmsr(MSR_AMD_10H_11H_STATUS);
> if (msr == id)
> break;
> ...
> }
> /* XXX Maybe your patch here? */
> ...
> }
>
> >> Besides, it introduces more delay and you may be reading the
> >> correct status because of that. :-P
> >
> > Having a separate reading pass does introduce more delay indeed.
> > Reading the correct status is a good thing, OTOH.
>
> That's what I said.
>
> > Why would anyone want to read incorrect status? (just want to note
> > that "correct" and "expected" are different things)
>
> Okay, okay.
>
> >> If people really think checking MSRC001_0071[18:16] is unworthy
> >> for
> >
> > Well, "other people" hasn't demonstrated/proved/convinced yet that
> > it is worthy
> >
> >> Bulldozer, I prefer skipping status check
> >
> > That's what I suggested from the very start.
>
> Buy me a Bulldozer and I'll fix it for you! :-P
If it's of any help, I have an Opteron 6274 I'd be willing to test some
patches on, to get Turbo Core working.
> >> but I disagree with this patch.
> >
> > Since I am not invested in this issue (I am not affected by the
> > problem and I do not have any personal attachment to the code in
> > question), I will just defer any decision to those who do care
> > about the problem. I hope that a fix will be provided in the end.
>
> Same here.
>
> Jung-uk Kim
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--
Theo
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