Messages in this thread | | | Date | Mon, 18 Jan 2016 19:06:14 +0100 | From | Peter Zijlstra <> | Subject | Re: [PATCH 09/11] x86, perf: Support sysfs files depending on SMT status |
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On Fri, Jan 15, 2016 at 05:12:51PM -0800, Andi Kleen wrote: > +ssize_t events_ht_sysfs_show(struct device *dev, struct device_attribute *attr, > + char *page) > +{ > + struct perf_pmu_events_ht_attr *pmu_attr = > + container_of(attr, struct perf_pmu_events_ht_attr, attr); > + > + /* > + * Report conditional events depending on Hyper-Threading. > + * > + * This is overly conservative as usually the HT special > + * handling is not needed if the other CPU thread is idle. > + * > + * Note this does not (cannot) handle the case when thread > + * siblings are invisible, for example with virtualization > + * if they are owned by some other guest. The user tool > + * has to re-read when a thread sibling gets onlined later. > + */ > + > + return sprintf(page, "%s", > + x86_pmu.ht_on ? > + pmu_attr->event_str_ht : > + pmu_attr->event_str_noht); > +}
So one obvious problem with this is that a concurrent hotplug operation can toggle ht_on resulting in bogus measurements.
I'm not sure there's anything we can do about that, other than WARN in the tool if it finds inconsistent results; does it?
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