powerpc: implement arch_scale_smt_power for Power7
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From: Peter Zijlstra on 2 Mar 2010 09:50 On Sat, 2010-02-27 at 21:21 +1100, Michael Neuling wrote: > In message <11927.1267010024(a)neuling.org> you wrote: > > > > If there's less the group will normally be balanced and we fall out and > > > > end up in check_asym_packing(). > > > > > > > > So what I tried doing with that loop is detect if there's a hole in the > > > > packing before busiest. Now that I think about it, what we need to check > > > > is if this_cpu (the removed cpu argument) is idle and less than busiest. > > > > > > > > So something like: > > > > > > > > static int check_asym_pacing(struct sched_domain *sd, > > > > struct sd_lb_stats *sds, > > > > int this_cpu, unsigned long *imbalance) > > > > { > > > > int busiest_cpu; > > > > > > > > if (!(sd->flags & SD_ASYM_PACKING)) > > > > return 0; > > > > > > > > if (!sds->busiest) > > > > return 0; > > > > > > > > busiest_cpu = group_first_cpu(sds->busiest); > > > > if (cpu_rq(this_cpu)->nr_running || this_cpu > busiest_cpu) > > > > return 0; > > > > > > > > *imbalance = (sds->max_load * sds->busiest->cpu_power) / > > > > SCHED_LOAD_SCALE; > > > > return 1; > > > > } > > > > > > > > Does that make sense? > > > > > > I think so. > > > > > > I'm seeing check_asym_packing do the right thing with the simple SMT2 > > > with 1 process case. It marks cpu0 as imbalanced when cpu0 is idle and > > > cpu1 is busy. > > > > > > Unfortunately the process doesn't seem to be get migrated down though. > > > Do we need to give *imbalance a higher value? > > > > So with ego help, I traced this down a bit more. > > > > In my simple test case (SMT2, t0 idle, t1 active) if f_b_g() hits our > > new case in check_asym_packing(), load_balance then runs f_b_q(). > > f_b_q() has this: > > > > if (capacity && rq->nr_running == 1 && wl > imbalance) > > continue; > > > > when check_asym_packing() hits, wl = 1783 and imbalance = 1024, so we > > continue and busiest remains NULL. > > > > load_balance then does "goto out_balanced" and it doesn't attempt to > > move the task. > > > > Based on this and on egos suggestion I pulled in Suresh Siddha patch > > from: http://lkml.org/lkml/2010/2/12/352. This fixes the problem. The > > process is moved down to t0. > > > > I've only tested SMT2 so far. > > I'm finding this SMT2 result to be unreliable. Sometimes it doesn't work > for the simple 1 process case. It seems to change boot to boot. > Sometimes it works as expected with t0 busy and t1 idle, but other times > it's the other way around. > > When it doesn't work, check_asym_packing() is still marking processes to > be pulled down but only gets run about 1 in every 4 calls to > load_balance(). > > For 2 of the other calls to load_balance, idle is CPU_NEWLY_IDLE and > hence check_asym_packing() doesn't get called. This results in > sd->nr_balance_failed being reset. When load_balance is next called and > check_asym_packing() hits, need_active_balance() returns 0 as > sd->nr_balance_failed is too small. This means the migration thread on > t1 is not woken and the process remains there. > > So why does thread0 change from NEWLY_IDLE to IDLE and visa versa, when > there is nothing running on it? Is this expected? Ah, yes, you should probably allow both those. NEWLY_IDLE is when we are about to schedule the idle thread, IDLE is when a tick hits the idle thread. I'm thinking that NEWLY_IDLE should also solve the NO_HZ case, since we'll have passed through that before we enter tickless state, just make sure SD_BALANCE_NEWIDLE is set on the relevant levels (should already be so). -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo(a)vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/ |