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SubjectRe: [PATCH v3 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs
On Fri, 07 Nov, at 01:06:12PM, Peter Zijlstra wrote:
> On Thu, Nov 06, 2014 at 12:23:21PM +0000, Matt Fleming wrote:
> > +/*
> > + * Exchange the RMID of a group of events.
> > + */
> > +static unsigned int
> > +intel_cqm_xchg_rmid(struct perf_event *group, unsigned int rmid)
> > +{
> > + struct perf_event *event;
> > + unsigned int old_rmid = group->hw.cqm_rmid;
> > + struct list_head *head = &group->hw.cqm_group_entry;
> > +
> > + lockdep_assert_held(&cache_mutex);
> > +
> > + /*
> > + * If our RMID is being deallocated, perform a read now.
> > + */
> > + if (__rmid_valid(old_rmid) && !__rmid_valid(rmid)) {
> > + struct intel_cqm_count_info info;
> > +
> > + local64_set(&group->count, 0);
> > + info.event = group;
> > +
> > + preempt_disable();
> > + smp_call_function_many(&cqm_cpumask, __intel_cqm_event_count,
> > + &info, 1);
> > + preempt_enable();
> > + }
>
> This suffers the same issue as before, why not call that one function
> and not reimplement it?
>
> Also, I don't think we'd ever swap an rmid for another valid one, right?
> So we could do this read/update unconditionally.

No, we never swap a valid RMID for another valid one, but we do make a
invalid -> valid transition, so doing the read wouldn't make sense
in that situation.

--
Matt Fleming, Intel Open Source Technology Center


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