On Thu, May 7, 2020 at 2:47 PM Andi Kleen <ak@xxxxxxxxxxxxxxx> wrote: > > > > - without this change events within a metric may get scheduled > > > together, after they may appear as part of a larger group and be > > > multiplexed at different times, lowering accuracy - however, less > > > multiplexing may compensate for this. > > > > I agree the heuristic in this patch set is naive and would welcome to > > improve it from your toplev experience. I think this change is > > progress on TopDownL1 - would you agree? > > TopdownL1 in non SMT mode should always fit. Inside a group > deduping always makes sense. > > The problem is SMT mode where it doesn't fit. toplev tries > to group each node and each level together. Thanks Andi, I've provided some examples of TopDownL3_SMT in the cover letter of the v3 patch set: https://lore.kernel.org/lkml/20200508053629.210324-1-irogers@xxxxxxxxxx/ I tested sandybridge and cascadelake and the results look similar to the non-SMT version. Let me know if there's a different variant to test. > > > > I'm wondering if what is needed are flags to control behavior. For > > example, avoiding the use of groups altogether. For TopDownL1 I see. > > Yes the current situation isn't great. > > For Topdown your patch clearly is an improvement, I'm not sure > it's for everything though. > > Probably the advanced heuristics are only useful for a few > formulas, most are very simple. So maybe it's ok. I guess > would need some testing over the existing formulas. Agreed, do you have a pointer on a metric group where things would obviously be worse? I started off with a cache miss and hit rate metric and similar to topdown this approach is a benefit. In v3 I've added a --metric-no-merge option to retain existing grouping behavior, I've also added a --metric-no-group that avoids groups for all metrics. This may be useful if the NMI watchdog can't be disabled. Thanks for the input! Ian > -Andi
