On Wed, Oct 22, 2014 at 11:04:31PM +0200, Stephane Eranian wrote: > Here is a simple case: > Limiting each HT to only 2 counters, can be any, 2 out of 4 possible. > > HT0: you measure a MEM* in ctr2, it is started first, and it keeps running > HT1: you measure PREC_DIST with PEBS (it requires ctr2) > > HT0 is measuring a corrupting event on ctr2, this prevents ctr2 on HT1 > from being used. > HT1 is starved, it cannot measure PREC_DIST > > Yes you have a quota of 2 out of 4 counters. > > The quota dynamic or static can help mitigate the starvation. The only > way to eliminate > it is to force multiplexing even though you are using fewer counters > than actually avail.
Ah yes, the very narrowly constrained events. Those suck indeed. And I imagine rotation might not even help here -- rotation doesn't guarantee SMT1 will try and schedule before SMT0, in fact there are setups (staggered tick) where its almost guaranteed not to. Still I suppose for 'normal' event its a much better state, SMT1 can always schedule some events. -- 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/
