lkml.org 
[lkml]   [2014]   [Jan]   [14]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [patch/rfc] perf on raspberry-pi without overflow interrupt
On Mon, Jan 13, 2014 at 11:55:17PM -0500, Vince Weaver wrote:
> On Fri, 10 Jan 2014, Peter Zijlstra wrote:
>
> > On Thu, Jan 09, 2014 at 11:08:47PM -0500, Vince Weaver wrote:
> > > On Thu, 9 Jan 2014, Will Deacon wrote:
> > >
> > > > I'd rather see it in the generic code if at all possible. Maybe we could add
> > > > a flags field to perf_pmu_register?
> > >
> > > I can look into adding the check in generic code.
> >
> > Adding something like this to the generic code would mean adding a
> > struct pmu capabilities field and visiting all existing PMU
> > implementations to properly fill this out.
>
> I don't see an existing pmu capabilities struct... or do you mean
> coming up with one?

Yeah, adding one.

> Would it only hold an "overflow_interrupt_available" flag, or are
> there other generic capabilities it would be handy to know about?

Possible (other) flags could be:

PMU_HAS_INT -- would allow sampling events
PMU_HAS_PRECISE -- would allow any ::precise value
PMU_HAS_FILTER -- would allow all os/user/etc. flags

> > There's a number of hardware PMU implementations that do not have an
> > interrupt and would need to set this flag.
>
> Well that can be added gradually, right? Things wouldn't get any worse if
> we add a generic check without auditing all code, things will just behave
> the same as before for those architectures.

Right, doing a sweep once every so often is useful to find more patterns
though.

> There is some subtlety here though. On ARM (or at least rasp-pi) the
> overflow hardware is there, just no interrupt is hooked up. So things
> like counter overflow are handled as long as overflows aren't faster than
> context switch time. It's just sampled events aren't possible.
>
> On architectures without overflow support at all (I've had such hardware;
> some SPARC machines, the Playstation 3 hypervisor) then counter overflow
> isn't possible without a periodic timer (sort of like what is done with
> Intel uncore). Is that something that should be in generic code too?

Maybe yeah, if there's enough replication of this it certainly makes
sense to lift it into generic code.


\
 
 \ /
  Last update: 2014-01-14 12:41    [W:0.053 / U:2.784 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site