On Mon, Oct 14, 2024 at 11:40:21AM -0400, Liang, Kan wrote:
>
>
> On 2024-10-14 7:56 a.m., Peter Zijlstra wrote:
> > On Thu, Aug 01, 2024 at 04:58:23AM +0000, Mingwei Zhang wrote:
> >
> >> @@ -5941,8 +5942,21 @@ void perf_put_mediated_pmu(void)
> >> }
> >> EXPORT_SYMBOL_GPL(perf_put_mediated_pmu);
> >>
> >> +static void perf_switch_interrupt(bool enter, u32 guest_lvtpc)
> >> +{
> >> + /* Mediated passthrough PMU should have PASSTHROUGH_VPMU cap. */
> >> + if (!passthru_pmu)
> >> + return;
> >> +
> >> + if (passthru_pmu->switch_interrupt &&
> >> + try_module_get(passthru_pmu->module)) {
> >> + passthru_pmu->switch_interrupt(enter, guest_lvtpc);
> >> + module_put(passthru_pmu->module);
> >> + }
> >> +}
> >
> > Should we move the whole module reference to perf_pmu_(,un}register() ?
>
> A PMU module can be load/unload anytime. How should we know if the PMU
> module is available when the reference check is moved to
> perf_pmu_(,un}register()?
Feh, dunno. I never really use modules. I just think the above is naf --
doubly so because you're saying the SRCU smp_mb() are expensive; but
this module reference crap is more expensive than that.
(IOW, the SRCU smp_mb() cannot have been the problem)
