Messages in this thread | | | Date | Thu, 12 Jan 2006 10:39:10 -0800 | From | Martin Bligh <> | Subject | Re: -mm seems significanty slower than mainline on kernbench |
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>> >> But I was thinking more about the code that (in the original) handled >> the case where the number of tasks to be moved was less than 1 but >> more than 0 (i.e. the cases where "imbalance" would have been reduced >> to zero when divided by SCHED_LOAD_SCALE). I think that I got that >> part wrong and you can end up with a bias load to be moved which is >> less than any of the bias_prio values for any queued tasks (in >> circumstances where the original code would have rounded up to 1 and >> caused a move). I think that the way to handle this problem is to >> replace 1 with "average bias prio" within that logic. This would >> guarantee at least one task with a bias_prio small enough to be moved. >> >> I think that this analysis is a strong argument for my original patch >> being the cause of the problem so I'll go ahead and generate a fix. >> I'll try to have a patch available later this morning. > > > Attached is a patch that addresses this problem. Unlike the description > above it does not use "average bias prio" as that solution would be very > complicated. Instead it makes the assumption that NICE_TO_BIAS_PRIO(0) > is a "good enough" for this purpose as this is highly likely to be the > median bias prio and the median is probably better for this purpose than > the average. > > Signed-off-by: Peter Williams <pwil3058@bigpond.com.au>
Doesn't fix the perf issue.
M.
> Peter > > > ------------------------------------------------------------------------ > > Index: MM-2.6.X/kernel/sched.c > =================================================================== > --- MM-2.6.X.orig/kernel/sched.c 2006-01-12 09:23:38.000000000 +1100 > +++ MM-2.6.X/kernel/sched.c 2006-01-12 10:44:50.000000000 +1100 > @@ -2116,11 +2116,11 @@ find_busiest_group(struct sched_domain * > (avg_load - this_load) * this->cpu_power) > / SCHED_LOAD_SCALE; > > - if (*imbalance < SCHED_LOAD_SCALE) { > + if (*imbalance < NICE_TO_BIAS_PRIO(0) * SCHED_LOAD_SCALE) { > unsigned long pwr_now = 0, pwr_move = 0; > unsigned long tmp; > > - if (max_load - this_load >= SCHED_LOAD_SCALE*2) { > + if (max_load - this_load >= NICE_TO_BIAS_PRIO(0) * SCHED_LOAD_SCALE*2) { > *imbalance = NICE_TO_BIAS_PRIO(0); > return busiest; > }
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