On 10/29/24 08:05, Jeff Law wrote: > On 10/20/24 1:40 PM, Vineet Gupta wrote: >> Pressure senstive scheduling seems to prefer "wide" schedules with more >> parallelism tending to more spills. This works better for in-order >> cores [1][2]. > I'm not really sure I'd characterize it that way, but I can also see how > you got to the wide vs narrow characterization. > > In my mind what we're really doing is refining a bit of the pressure > reduction heuristic to more accurately reflect the result of issuing > insns that reduce pressure. So it's more like a level of how > aggressively we try to reduce pressure.
Right, this characterization wasn't my first choice either but from earlier discussions on the list it seems the existing behavior was "as-designed" and more of a feature than anti-feature. So I wanted this patch to come out as neutral vs. being pejorative (as in it makes spilling less aggressive)... >> This patch allows for an opt-in target hook >> TARGET_SCHED_PRESSURE_PREFER_NARROW: >> >> - The default hook (returns false) preserves existing behavior of wider >> schedules, more parallelism and potentially more spills. >> >> - targets implementing the hook as true get the reverse effect. > I think we need a better name/description here. If SCHED_PRESSURE_MODEL > was a target hook then I'd probably be looking to make it an integer > indicating how aggressively to try and reduce pressure. So perhaps > TARGET_SCHED_PRESSURE_AGGRESSIVE? I don't particularly like it, but I > like it better than the PREFER_NARROW idea. Everything else I've come > up with has been scarily verbose. > > TARGET_SCHED_PRESSURE_INCLUDE_PRESSURE_REDUCING_INSNS is on the absurd > side. Removing the second PRESSURE makes me think of vector reductions, > so I didn't want to do that :-) > > Certainly open to more ideas on the naming, which I think will impact > the documentation & comments as well. > > And to be 100% clear, no concerns with the behavior of the patch, it's > really just the naming convention, documentation/comments. > > Thoughts? I agree the NARROW/WIDE stuff is obfuscating things in technicalities. How about TARGET_SCHED_PRESSURE_SPILL_AGGRESSIVE with true (default) being existing behavior and false being new semantics. Its a bit verbose but I think clear enough. > ps. I've got to get out of my bubble more often. Picked up a bug at > the RVI summit... Clearly my immune system isn't firing on all cylinders. Oh gosh. Get well soon ! Thx, -Vineet
