Messages in this thread | | | From | Andi Kleen <> | Subject | Re: [PATCH v1 1/2] perf,x86: add Intel RAPL PMU support | Date | Mon, 07 Oct 2013 14:45:44 -0700 |
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Stephane Eranian <eranian@google.com> writes: > >>> + goto again; >>> + >>> + struct rapl_pmu *pmu = __get_cpu_var(rapl_pmu); >>> + >>> + if (WARN_ON_ONCE(!(event->hw.state & PERF_HES_STOPPED))) >>> + return; >>> + >>> + event->hw.state = 0; >>> + >>> + local64_set(&event->hw.prev_count, rapl_read_counter(event)); >>> + >>> + pmu->n_active++; >> >> What lock protects this add? >> > None. I will add one. Bu then I am wondering about if it is really > necessary given > that RAPL event are system-wide and this pinned to a CPU. If the call came > from another CPU, then it IPI there, and that means that CPU is executing that > code. Any other CPU will need IPI too, and that interrupt will be kept pending. > Am I missing a test case here? Are IPI reentrant?
they can be if interrupts are enabled (likely here)
> >>> +} >>> + >>> +static ssize_t rapl_get_attr_cpumask(struct device *dev, >>> + struct device_attribute *attr, char *buf) >>> +{ >>> + int n = cpulist_scnprintf(buf, PAGE_SIZE - 2, &rapl_cpu_mask); >> >> Check n here in case it overflowed >> > But isn't that what the -2 and the below \n\0 are for?
I know it's very unlikely and other stuff would break, but
Assuming you have a system with some many CPUs that they don't fit into a page. Then the scnprintf would fail, but you would corrupt random data because you write before the buffer.
>> Doesn't this need a lock of some form? AFAIK we can do parallel >> CPU startup now. >> > Did not know about this change? But then that means all the other > perf_event *_starting() and maybe even _*prepare() routines must also > use locks. I can add that to RAPL.
Yes may be broken everywhere.
>>> + /* check supported CPU */ >>> + switch (boot_cpu_data.x86_model) { >>> + case 42: /* Sandy Bridge */ >>> + case 58: /* Ivy Bridge */ >>> + case 60: /* Haswell */ >> >> Need more model numbers for Haswell (see the main perf driver) >> > Don't have all the models to test...
It should be all the same.
-Andi -- ak@linux.intel.com -- Speaking for myself only
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