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Date: Mon, 21 Jan 2013 10:50:11 +0800
From: Michael Wang <wangyun@...ux.vnet.ibm.com>
To: Mike Galbraith <bitbucket@...ine.de>
CC: linux-kernel@...r.kernel.org, mingo@...hat.com,
peterz@...radead.org, mingo@...nel.org, a.p.zijlstra@...llo.nl
Subject: Re: [RFC PATCH 0/2] sched: simplify the select_task_rq_fair()
On 01/20/2013 12:09 PM, Mike Galbraith wrote:
> On Thu, 2013-01-17 at 13:55 +0800, Michael Wang wrote:
>> Hi, Mike
>>
>> I've send out the v2, which I suppose it will fix the below BUG and
>> perform better, please do let me know if it still cause issues on your
>> arm7 machine.
>
> s/arm7/aim7
>
> Someone swiped half of CPUs/ram, so the box is now 2 10 core nodes vs 4.
>
> stock scheduler knobs
>
> 3.8-wang-v2 avg 3.8-virgin avg vs wang
> Tasks jobs/min
> 1 436.29 435.66 435.97 435.97 437.86 441.69 440.09 439.88 1.008
> 5 2361.65 2356.14 2350.66 2356.15 2416.27 2563.45 2374.61 2451.44 1.040
> 10 4767.90 4764.15 4779.18 4770.41 4946.94 4832.54 4828.69 4869.39 1.020
> 20 9672.79 9703.76 9380.80 9585.78 9634.34 9672.79 9727.13 9678.08 1.009
> 40 19162.06 19207.61 19299.36 19223.01 19268.68 19192.40 19056.60 19172.56 .997
> 80 37610.55 37465.22 37465.22 37513.66 37263.64 37120.98 37465.22 37283.28 .993
> 160 69306.65 69655.17 69257.14 69406.32 69257.14 69306.65 69257.14 69273.64 .998
> 320 111512.36 109066.37 111256.45 110611.72 108395.75 107913.19 108335.20 108214.71 .978
> 640 142850.83 148483.92 150851.81 147395.52 151974.92 151263.65 151322.67 151520.41 1.027
> 1280 52788.89 52706.39 67280.77 57592.01 189931.44 189745.60 189792.02 189823.02 3.295
> 2560 75403.91 52905.91 45196.21 57835.34 217368.64 217582.05 217551.54 217500.74 3.760
>
> sched_latency_ns = 24ms
> sched_min_granularity_ns = 8ms
> sched_wakeup_granularity_ns = 10ms
>
> 3.8-wang-v2 avg 3.8-virgin avg vs wang
> Tasks jobs/min
> 1 436.29 436.60 434.72 435.87 434.41 439.77 438.81 437.66 1.004
> 5 2382.08 2393.36 2451.46 2408.96 2451.46 2453.44 2425.94 2443.61 1.014
> 10 5029.05 4887.10 5045.80 4987.31 4844.12 4828.69 4844.12 4838.97 .970
> 20 9869.71 9734.94 9758.45 9787.70 9513.34 9611.42 9565.90 9563.55 .977
> 40 19146.92 19146.92 19192.40 19162.08 18617.51 18603.22 18517.95 18579.56 .969
> 80 37177.91 37378.57 37292.31 37282.93 36451.13 36179.10 36233.18 36287.80 .973
> 160 70260.87 69109.05 69207.71 69525.87 68281.69 68522.97 68912.58 68572.41 .986
> 320 114745.56 113869.64 114474.62 114363.27 114137.73 114137.73 114137.73 114137.73 .998
> 640 164338.98 164338.98 164618.00 164431.98 164130.34 164130.34 164130.34 164130.34 .998
> 1280 209473.40 209134.54 209473.40 209360.44 210040.62 210040.62 210097.51 210059.58 1.003
> 2560 242703.38 242627.46 242779.34 242703.39 244001.26 243847.85 243732.91 243860.67 1.004
>
> As you can see, the load collapsed at the high load end with stock
> scheduler knobs (desktop latency). With knobs set to scale, the delta
> disappeared.
Thanks for the testing, Mike, please allow me to ask few questions.
What are those tasks actually doing? what's the workload?
And I'm confusing about how those new parameter value was figured out
and how could them help solve the possible issue?
Do you have any idea about which part in this patch set may cause the issue?
One change by designed is that, for old logical, if it's a wake up and
we found affine sd, the select func will never go into the balance path,
but the new logical will, in some cases, do you think this could be a
problem?
>
> I thought perhaps the bogus (shouldn't exist) CPU domain in mainline
> somehow contributes to the strange behavioral delta, but killing it made
> zero difference. All of these numbers for both trees were logged with
> the below applies, but as noted, it changed nothing.
The patch set was supposed to do accelerate by reduce the cost of
select_task_rq(), so it should be harmless for all the conditions.
Regards,
Michael Wang
>
> From: Alex Shi <alex.shi@...el.com>
> Date: Mon, 17 Dec 2012 09:42:57 +0800
> Subject: [PATCH 01/18] sched: remove SD_PERFER_SIBLING flag
>
> The flag was introduced in commit b5d978e0c7e79a. Its purpose seems
> trying to fullfill one node first in NUMA machine via pulling tasks
> from other nodes when the node has capacity.
>
> Its advantage is when few tasks share memories among them, pulling
> together is helpful on locality, so has performance gain. The shortage
> is it will keep unnecessary task migrations thrashing among different
> nodes, that reduces the performance gain, and just hurt performance if
> tasks has no memory cross.
>
> Thinking about the sched numa balancing patch is coming. The small
> advantage are meaningless to us, So better to remove this flag.
>
> Reported-by: Mike Galbraith <efault@....de>
> Signed-off-by: Alex Shi <alex.shi@...el.com>
> ---
> include/linux/sched.h | 1 -
> include/linux/topology.h | 2 --
> kernel/sched/core.c | 1 -
> kernel/sched/fair.c | 19 +------------------
> 4 files changed, 1 insertion(+), 22 deletions(-)
>
> diff --git a/include/linux/sched.h b/include/linux/sched.h
> index 5dafac3..6dca96c 100644
> --- a/include/linux/sched.h
> +++ b/include/linux/sched.h
> @@ -836,7 +836,6 @@ enum cpu_idle_type {
> #define SD_SHARE_PKG_RESOURCES 0x0200 /* Domain members share cpu pkg resources */
> #define SD_SERIALIZE 0x0400 /* Only a single load balancing instance */
> #define SD_ASYM_PACKING 0x0800 /* Place busy groups earlier in the domain */
> -#define SD_PREFER_SIBLING 0x1000 /* Prefer to place tasks in a sibling domain */
> #define SD_OVERLAP 0x2000 /* sched_domains of this level overlap */
>
> extern int __weak arch_sd_sibiling_asym_packing(void);
> diff --git a/include/linux/topology.h b/include/linux/topology.h
> index d3cf0d6..15864d1 100644
> --- a/include/linux/topology.h
> +++ b/include/linux/topology.h
> @@ -100,7 +100,6 @@ int arch_update_cpu_topology(void);
> | 1*SD_SHARE_CPUPOWER \
> | 1*SD_SHARE_PKG_RESOURCES \
> | 0*SD_SERIALIZE \
> - | 0*SD_PREFER_SIBLING \
> | arch_sd_sibling_asym_packing() \
> , \
> .last_balance = jiffies, \
> @@ -162,7 +161,6 @@ int arch_update_cpu_topology(void);
> | 0*SD_SHARE_CPUPOWER \
> | 0*SD_SHARE_PKG_RESOURCES \
> | 0*SD_SERIALIZE \
> - | 1*SD_PREFER_SIBLING \
> , \
> .last_balance = jiffies, \
> .balance_interval = 1, \
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 5dae0d2..8ed2784 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -6014,7 +6014,6 @@ sd_numa_init(struct sched_domain_topology_level *tl, int cpu)
> | 0*SD_SHARE_CPUPOWER
> | 0*SD_SHARE_PKG_RESOURCES
> | 1*SD_SERIALIZE
> - | 0*SD_PREFER_SIBLING
> | sd_local_flags(level)
> ,
> .last_balance = jiffies,
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index 59e072b..5d175f2 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -4339,13 +4339,9 @@ static bool update_sd_pick_busiest(struct lb_env *env,
> static inline void update_sd_lb_stats(struct lb_env *env,
> int *balance, struct sd_lb_stats *sds)
> {
> - struct sched_domain *child = env->sd->child;
> struct sched_group *sg = env->sd->groups;
> struct sg_lb_stats sgs;
> - int load_idx, prefer_sibling = 0;
> -
> - if (child && child->flags & SD_PREFER_SIBLING)
> - prefer_sibling = 1;
> + int load_idx;
>
> load_idx = get_sd_load_idx(env->sd, env->idle);
>
> @@ -4362,19 +4358,6 @@ static inline void update_sd_lb_stats(struct lb_env *env,
> sds->total_load += sgs.group_load;
> sds->total_pwr += sg->sgp->power;
>
> - /*
> - * In case the child domain prefers tasks go to siblings
> - * first, lower the sg capacity to one so that we'll try
> - * and move all the excess tasks away. We lower the capacity
> - * of a group only if the local group has the capacity to fit
> - * these excess tasks, i.e. nr_running < group_capacity. The
> - * extra check prevents the case where you always pull from the
> - * heaviest group when it is already under-utilized (possible
> - * with a large weight task outweighs the tasks on the system).
> - */
> - if (prefer_sibling && !local_group && sds->this_has_capacity)
> - sgs.group_capacity = min(sgs.group_capacity, 1UL);
> -
> if (local_group) {
> sds->this_load = sgs.avg_load;
> sds->this = sg;
>
>
--
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