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Date: Tue, 24 Nov 2009 07:36:53 +0100 From: Nick Piggin <npiggin@...e.de> To: Ingo Molnar <mingo@...e.hu> Cc: Peter Zijlstra <peterz@...radead.org>, Linux Kernel Mailing List <linux-kernel@...r.kernel.org> Subject: Re: newidle balancing in NUMA domain? On Mon, Nov 23, 2009 at 01:46:15PM +0100, Ingo Molnar wrote: > > * Nick Piggin <npiggin@...e.de> wrote: > > > > (I hope i explained my point clearly enough.) > > > > > > No argument that it could be done cleaner - the duality right now of > > > both having the fuzzy stats and the rate limiting should be decided > > > one way or another. > > > > Well, I would say please keep domain balancing behaviour at least > > somewhat close to how it was with O(1) scheduler at least until CFS is > > more sorted out. There is no need to knee jerk because BFS is better > > at something. > > Well, see the change (commit 0ec9fab3d) attached below - even in > hindsight it was well argued by Mike with quite a few numbers: +68% in > x264 performance. Quite a few being one test case, and on a program with a horrible parallelism design (rapid heavy weight forks to distribute small units of work). > If you think it's a bad change (combined with newidle-rate-limit) then > please show the numbers that counter it and preferably extend 'perf > bench sched' with the testcases that you care about most. > > IIRC (and Peter mentioned this too) Mike got into the whole kbuild angle > due to comparing mainline scheduler to BFS - but that's really a > positive thing IMO, not some "knee-jerk reaction". It is a knee-jerk "we have to be better than BFS" reaction. It is quite obvious that vasty increasing inter node balancing and remote cacheline touches is not a good idea (unless it helps _reasonably_ designed programs without unduely hurting others). And when you are changing all this desktop interactivity stuff, I would ask please not to make these kinds of "improvements" to domains balancing. I don't think that is too much to ask given track record of scheduler problems. Finally, I didn't realise I would have to be responsible for shooting down every "ooh shiny" change that gets pushed into the scheduler. I would have hoped they are ensured to be rather well thought out and reviewed and tested first. I do think it is a bad change, for extensive reasons I explained. It will obviously cause regressions on workloads with lots of newidle events that are un-balanceable (which would include _well tuned_ net work and data base servers). And it does. I thought you'd have been aware of that. http://patchwork.kernel.org/patch/58931/ > > Ingo > > -----------------------> > >From 0ec9fab3d186d9cbb00c0f694d4a260d07c198d9 Mon Sep 17 00:00:00 2001 > From: Mike Galbraith <efault@....de> > Date: Tue, 15 Sep 2009 15:07:03 +0200 > Subject: [PATCH] sched: Improve latencies and throughput > > Make the idle balancer more agressive, to improve a > x264 encoding workload provided by Jason Garrett-Glaser: > > NEXT_BUDDY NO_LB_BIAS > encoded 600 frames, 252.82 fps, 22096.60 kb/s > encoded 600 frames, 250.69 fps, 22096.60 kb/s > encoded 600 frames, 245.76 fps, 22096.60 kb/s > > NO_NEXT_BUDDY LB_BIAS > encoded 600 frames, 344.44 fps, 22096.60 kb/s > encoded 600 frames, 346.66 fps, 22096.60 kb/s > encoded 600 frames, 352.59 fps, 22096.60 kb/s > > NO_NEXT_BUDDY NO_LB_BIAS > encoded 600 frames, 425.75 fps, 22096.60 kb/s > encoded 600 frames, 425.45 fps, 22096.60 kb/s > encoded 600 frames, 422.49 fps, 22096.60 kb/s > > Peter pointed out that this is better done via newidle_idx, > not via LB_BIAS, newidle balancing should look for where > there is load _now_, not where there was load 2 ticks ago. > > Worst-case latencies are improved as well as no buddies > means less vruntime spread. (as per prior lkml discussions) > > This change improves kbuild-peak parallelism as well. > > Reported-by: Jason Garrett-Glaser <darkshikari@...il.com> > Signed-off-by: Mike Galbraith <efault@....de> > Signed-off-by: Peter Zijlstra <a.p.zijlstra@...llo.nl> > LKML-Reference: <1253011667.9128.16.camel@...ge.simson.net> > Signed-off-by: Ingo Molnar <mingo@...e.hu> > --- > arch/ia64/include/asm/topology.h | 5 +++-- > arch/powerpc/include/asm/topology.h | 2 +- > arch/sh/include/asm/topology.h | 3 ++- > arch/x86/include/asm/topology.h | 4 +--- > include/linux/topology.h | 2 +- > kernel/sched_features.h | 2 +- > 6 files changed, 9 insertions(+), 9 deletions(-) > > diff --git a/arch/ia64/include/asm/topology.h b/arch/ia64/include/asm/topology.h > index 47f3c51..42f1673 100644 > --- a/arch/ia64/include/asm/topology.h > +++ b/arch/ia64/include/asm/topology.h > @@ -61,7 +61,7 @@ void build_cpu_to_node_map(void); > .cache_nice_tries = 2, \ > .busy_idx = 2, \ > .idle_idx = 1, \ > - .newidle_idx = 2, \ > + .newidle_idx = 0, \ > .wake_idx = 0, \ > .forkexec_idx = 1, \ > .flags = SD_LOAD_BALANCE \ > @@ -87,10 +87,11 @@ void build_cpu_to_node_map(void); > .cache_nice_tries = 2, \ > .busy_idx = 3, \ > .idle_idx = 2, \ > - .newidle_idx = 2, \ > + .newidle_idx = 0, \ > .wake_idx = 0, \ > .forkexec_idx = 1, \ > .flags = SD_LOAD_BALANCE \ > + | SD_BALANCE_NEWIDLE \ > | SD_BALANCE_EXEC \ > | SD_BALANCE_FORK \ > | SD_BALANCE_WAKE \ > diff --git a/arch/powerpc/include/asm/topology.h b/arch/powerpc/include/asm/topology.h > index a6b220a..1a2c9eb 100644 > --- a/arch/powerpc/include/asm/topology.h > +++ b/arch/powerpc/include/asm/topology.h > @@ -57,7 +57,7 @@ static inline int pcibus_to_node(struct pci_bus *bus) > .cache_nice_tries = 1, \ > .busy_idx = 3, \ > .idle_idx = 1, \ > - .newidle_idx = 2, \ > + .newidle_idx = 0, \ > .wake_idx = 0, \ > .flags = SD_LOAD_BALANCE \ > | SD_BALANCE_EXEC \ > diff --git a/arch/sh/include/asm/topology.h b/arch/sh/include/asm/topology.h > index 9054e5c..c843677 100644 > --- a/arch/sh/include/asm/topology.h > +++ b/arch/sh/include/asm/topology.h > @@ -15,13 +15,14 @@ > .cache_nice_tries = 2, \ > .busy_idx = 3, \ > .idle_idx = 2, \ > - .newidle_idx = 2, \ > + .newidle_idx = 0, \ > .wake_idx = 0, \ > .forkexec_idx = 1, \ > .flags = SD_LOAD_BALANCE \ > | SD_BALANCE_FORK \ > | SD_BALANCE_EXEC \ > | SD_BALANCE_WAKE \ > + | SD_BALANCE_NEWIDLE \ > | SD_SERIALIZE, \ > .last_balance = jiffies, \ > .balance_interval = 1, \ > diff --git a/arch/x86/include/asm/topology.h b/arch/x86/include/asm/topology.h > index 4b1b335..7fafd1b 100644 > --- a/arch/x86/include/asm/topology.h > +++ b/arch/x86/include/asm/topology.h > @@ -116,14 +116,12 @@ extern unsigned long node_remap_size[]; > > # define SD_CACHE_NICE_TRIES 1 > # define SD_IDLE_IDX 1 > -# define SD_NEWIDLE_IDX 2 > # define SD_FORKEXEC_IDX 0 > > #else > > # define SD_CACHE_NICE_TRIES 2 > # define SD_IDLE_IDX 2 > -# define SD_NEWIDLE_IDX 2 > # define SD_FORKEXEC_IDX 1 > > #endif > @@ -137,7 +135,7 @@ extern unsigned long node_remap_size[]; > .cache_nice_tries = SD_CACHE_NICE_TRIES, \ > .busy_idx = 3, \ > .idle_idx = SD_IDLE_IDX, \ > - .newidle_idx = SD_NEWIDLE_IDX, \ > + .newidle_idx = 0, \ > .wake_idx = 0, \ > .forkexec_idx = SD_FORKEXEC_IDX, \ > \ > diff --git a/include/linux/topology.h b/include/linux/topology.h > index c87edcd..4298745 100644 > --- a/include/linux/topology.h > +++ b/include/linux/topology.h > @@ -151,7 +151,7 @@ int arch_update_cpu_topology(void); > .cache_nice_tries = 1, \ > .busy_idx = 2, \ > .idle_idx = 1, \ > - .newidle_idx = 2, \ > + .newidle_idx = 0, \ > .wake_idx = 0, \ > .forkexec_idx = 1, \ > \ > diff --git a/kernel/sched_features.h b/kernel/sched_features.h > index 891ea0f..e98c2e8 100644 > --- a/kernel/sched_features.h > +++ b/kernel/sched_features.h > @@ -67,7 +67,7 @@ SCHED_FEAT(AFFINE_WAKEUPS, 1) > * wakeup-preemption), since its likely going to consume data we > * touched, increases cache locality. > */ > -SCHED_FEAT(NEXT_BUDDY, 1) > +SCHED_FEAT(NEXT_BUDDY, 0) > > /* > * Prefer to schedule the task that ran last (when we did -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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