Messages in this thread |  | | Date | Wed, 24 Sep 2014 21:27:39 +0100 | From | Matt Fleming <> | Subject | Re: [PATCH 08/11] perf/x86/intel: Add Intel Cache QoS Monitoring support |
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On Wed, 24 Sep, at 09:40:10AM, Andi Kleen wrote: > Matt Fleming <matt@console-pimps.org> writes: > > > > diff --git a/arch/x86/kernel/cpu/Makefile b/arch/x86/kernel/cpu/Makefile > > index 7e1fd4e08552..8abb18fbcd13 100644 > > --- a/arch/x86/kernel/cpu/Makefile > > +++ b/arch/x86/kernel/cpu/Makefile > > @@ -38,7 +38,7 @@ obj-$(CONFIG_CPU_SUP_INTEL) += perf_event_p6.o perf_event_knc.o perf_event_p4.o > > obj-$(CONFIG_CPU_SUP_INTEL) += perf_event_intel_lbr.o perf_event_intel_ds.o perf_event_intel.o > > obj-$(CONFIG_CPU_SUP_INTEL) += perf_event_intel_uncore.o perf_event_intel_uncore_snb.o > > obj-$(CONFIG_CPU_SUP_INTEL) += perf_event_intel_uncore_snbep.o perf_event_intel_uncore_nhmex.o > > -obj-$(CONFIG_CPU_SUP_INTEL) += perf_event_intel_rapl.o > > +obj-$(CONFIG_CPU_SUP_INTEL) += perf_event_intel_rapl.o perf_event_intel_cqm.o > > What's missing to be able to make this a module?
Not sure, that's not something I'd thought of. I simply copied every other PMU driver in this directory.
But as an experiment I tried it, and the only thing that appears to be necessary is adding EXPORT_SYMBOL_GPL() to events_sysfs_show.
> > + > > + /* > > + * Is @cpu a designated cqm reader? > > + */ > > + if (!cpumask_test_and_clear_cpu(cpu, &cqm_cpumask)) > > + return; > > + > > + for_each_online_cpu(i) { > > Likely possible cpus to avoid races? Otherwise you'll need more locking.
I was under the impression that CPU_DOWN_PREPARE notifiers were serialized against cpu hotplug. And reading the code, that does appear to be so.
What race have you got in mind?
> > +static int __init intel_cqm_init(void) > > +{ > > + int i, cpu, ret; > > + > > + if (!cpu_has(&boot_cpu_data, X86_FEATURE_CQM_OCCUP_LLC)) > > + return -ENODEV; > > This should use cpufeature.h
What? Please be more explicit.
> > + > > + cqm_l3_scale = boot_cpu_data.x86_cache_occ_scale; > > + > > + /* > > + * It's possible that not all resources support the same number > > + * of RMIDs. Instead of making scheduling much more complicated > > + * (where we have to match a task's RMID to a cpu that supports > > + * that many RMIDs) just find the minimum RMIDs supported across > > + * all cpus. > > + * > > + * Also, check that the scales match on all cpus. > > + */ > > + for_each_online_cpu(cpu) { > > And this should take the cpu hotplug lock (although it may be > latent at this point if it's only running at early initializion)
Good catch, this is racy. I'll fix this up.
> But in fact what good is the test then if you only > every likely check cpu #0?
We don't, we check every online cpu, not just cpu 0.
-- Matt Fleming, Intel Open Source Technology Center
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