Re: [patch] sched-2.5.59-A2

Erich Focht
2003-01-17T14:25:59Z

Hi Ingo,

I tried your patch on the small NEC TX7 I can access easilly (8
Itanium2 CPUs on 4 nodes). I actually used your patch on top of the
2.5.52-ia64 kernel, but that shouldn't matter.

I like the cleanup of the topology.h. Also the renaming to
prev_cpu_load. There was a mistake (I think) in the call to
load_balance() in the idle path, guess you wanted to have:
+ load_balance(this_rq, 1, __node_to_cpu_mask(this_node));
instead of
+ load_balance(this_rq, 1, this_cpumask);
otherwise you won't load balance at all for idle cpus.

Here are the results:

kernbench (average of 5 kernel compiles) (standard error in brackets)
---------
Elapsed UserTime SysTime
orig 134.43(1.79) 944.79(0.43) 21.41(0.28)
ingo 136.74(1.58) 951.55(0.73) 21.16(0.32)
ingofix 135.22(0.59) 952.17(0.78) 21.16(0.19)

hackbench (chat benchmark alike) (elapsed time for N groups of 20
--------- senders & receivers, stats from 10 measurements)

N=10 N=25 N=50 N=100
orig 0.77(0.03) 1.91(0.06) 3.77(0.06) 7.78(0.21)
ingo 1.70(0.35) 3.11(0.47) 4.85(0.55) 8.80(0.98)
ingofix 1.16(0.14) 2.67(0.53) 5.05(0.26) 9.99(0.13)

numabench (N memory intensive tasks running in parallel, disturbed for
--------- a short time by a "hackbench 10" call)

numa_test N=4 ElapsedTime TotalUserTime TotalSysTime
orig: 26.13(2.54) 86.10(4.47) 0.09(0.01)
ingo: 27.60(2.16) 88.06(4.58) 0.11(0.01)
ingofix: 25.51(3.05) 83.55(2.78) 0.10(0.01)

numa_test N=8 ElapsedTime TotalUserTime TotalSysTime
orig: 24.81(2.71) 164.94(4.82) 0.17(0.01)
ingo: 27.38(3.01) 170.06(5.60) 0.30(0.03)
ingofix: 29.08(2.79) 172.10(4.48) 0.32(0.03)

numa_test N=16 ElapsedTime TotalUserTime TotalSysTime
orig: 45.19(3.42) 332.07(5.89) 0.32(0.01)
ingo: 50.18(0.38) 359.46(9.31) 0.46(0.04)
ingofix: 50.30(0.42) 357.38(9.12) 0.46(0.01)

numa_test N=32 ElapsedTime TotalUserTime TotalSysTime
orig: 86.84(1.83) 671.99(9.98) 0.65(0.02)
ingo: 93.44(2.13) 704.90(16.91) 0.82(0.06)
ingofix: 93.92(1.28) 727.58(9.26) 0.77(0.03)

>From these results I would prefer to either leave the numa scheduler
as it is or to introduce an IDLE_NODEBALANCE_TICK and a
BUSY_NODEBALANCE_TICK instead of just having one NODE_REBALANCE_TICK
which balances very rarely. In that case it would make sense to keep
the cpus_to_balance() function.

Best regards,
Erich

On Friday 17 January 2003 09:47, Ingo Molnar wrote:
> Martin, Erich,
>
> could you give the attached patch a go, it implements my
> cleanup/reorganization suggestions ontop of 2.5.59:
>
> - decouple the 'slow' rebalancer from the 'fast' rebalancer and attach it
> to the scheduler tick. Remove rq->nr_balanced.
>
> - do idle-rebalancing every 1 msec, intra-node rebalancing every 200
> msecs and inter-node rebalancing every 400 msecs.
>
> - move the tick-based rebalancing logic into rebalance_tick(), it looks
> more organized this way and we have all related code in one spot.
>
> - clean up the topology.h include file structure. Since generic kernel
> code uses all the defines already, there's no reason to keep them in
> asm-generic.h. I've created a linux/topology.h file that includes
> asm/topology.h and takes care of the default and generic definitions.
> Moved over a generic topology definition from mmzone.h.
>
> - renamed rq->prev_nr_running[] to rq->prev_cpu_load[] - this further
> unifies the SMP and NUMA balancers and is more in line with the
> prev_node_load name.
>
> If performance drops due to this patch then the benchmarking goal would be
> to tune the following frequencies:
>
> #define IDLE_REBALANCE_TICK (HZ/1000 ?: 1)
> #define BUSY_REBALANCE_TICK (HZ/5 ?: 1)
> #define NODE_REBALANCE_TICK (BUSY_REBALANCE_TICK * 2)
>
> In theory NODE_REBALANCE_TICK could be defined by the NUMA platform,
> although in the past such per-platform scheduler tunings used to end
> 'orphaned' after some time. 400 msecs is pretty conservative at the
> moment, it could be made more frequent if benchmark results support it.
>
> the patch compiles and boots on UP and SMP, it compiles on x86-NUMA.
>
> Ingo