On Wed, May 28, 2014 at 6:51 PM, Andi Kleen <[email protected]> wrote: >> The only part I don't quite follow here is this: >> if (__test_and_set_bit(bit, (unsigned long *)&status)) >> continue; >> >> Which seems to indicate the code is making sure each counter is >> processed only once. But it can only be processed once, if you have >> only one record. And if you have multiple, you want to be able to >> handle the same counter multiple times, at least once perf PEBS >> record. So I am a bit confused about this test. > > Each PEBS record is only for a single counter overflow. So it > always should only be a single perf event. > So, you're telling me this is a sanity check. That p->status can only have one bit set. Somehow that's not how I recall it working.
The point is that a single PEBS record is enough for multiple events when the overflows occur simultaneously because they all get the same machine state which is correct. A single entry also saves space in the buffer. -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
