Messages in this thread | | | Date | Mon, 10 Nov 2014 21:58:46 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH v3 10/11] perf/x86/intel: Perform rotation on Intel CQM RMIDs |
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On Mon, Nov 10, 2014 at 08:43:53PM +0000, Matt Fleming wrote: > 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.
Ah indeed.
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