On Sat, Sep 27, 2014 at 06:47:41PM +0200, Frederic Weisbecker wrote: Trim replies already -- I should really go write that auto-bounce for excessive quoting already.
> I wonder if it's worth to create such an arch callback and core corner case. > How about just scheduling out then in the events that have lbr, wouldn't we > have more simple code in the end? That depends a bit, the lbr save/restore is indeed very expensive (at least 16 msr reads and 16 msr writes -- when assuming 16 deep lbr), but this is still on about the same order of msr writes required to switch 4 counters (esp. if we include the PEBS msrs). So at that point we still win about half the context switch cost by not doing an unconditional sched out / sched in. Also, there are more consumers of this thing. > Besides, BTS would benefit from that too. I can't seem to find where it is > flushed when a task context switches inside a same perf context. It seems > that it doesn't happen, BTS traces are flushed only on event stop (and > overflow IRQ) > and events aren't stopped if a context switch happens in the same perf > context. > Having Y task bts traces from task X event is probably not what we want. Flushing the BTS is indeed a good point, but that would definitely benefit from this, draining the BTS buffer is likely faster than doing all those MSR writes. -- 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/
