Re: [PATCH] sched/fair: ensure tasks spreading in LLC during LB
On Mon, Nov 02, 2020 at 11:24:57AM +0100, Vincent Guittot wrote: > schbench shows latency increase for 95 percentile above since: > commit 0b0695f2b34a ("sched/fair: Rework load_balance()") > > Align the behavior of the load balancer with the wake up path, which tries > to select an idle CPU which belongs to the LLC for a waking task. > > calculate_imbalance() will use nr_running instead of the spare > capacity when CPUs share resources (ie cache) at the domain level. This > will ensure a better spread of tasks on idle CPUs. > > Running schbench on a hikey (8cores arm64) shows the problem: > > tip/sched/core : > schbench -m 2 -t 4 -s 1 -c 100 -r 10 > Latency percentiles (usec) > 50.0th: 33 > 75.0th: 45 > 90.0th: 51 > 95.0th: 4152 > *99.0th: 14288 > 99.5th: 14288 > 99.9th: 14288 > min=0, max=14276 > > tip/sched/core + patch : > schbench -m 2 -t 4 -s 1 -c 100 -r 10 > Latency percentiles (usec) > 50.0th: 34 > 75.0th: 47 > 90.0th: 52 > 95.0th: 78 > *99.0th: 94 > 99.5th: 94 > 99.9th: 94 > min=0, max=94 > > Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()") > Reported-by: Chris Mason > Suggested-by: Rik van Riel > Signed-off-by: Vincent Guittot Acked-by: Mel Gorman -- Mel Gorman SUSE Labs
Re: [PATCH] sched/fair: ensure tasks spreading in LLC during LB
On Mon, Nov 02, 2020 at 11:24:57AM +0100, Vincent Guittot wrote: > schbench shows latency increase for 95 percentile above since: > commit 0b0695f2b34a ("sched/fair: Rework load_balance()") > > Align the behavior of the load balancer with the wake up path, which tries > to select an idle CPU which belongs to the LLC for a waking task. > > calculate_imbalance() will use nr_running instead of the spare > capacity when CPUs share resources (ie cache) at the domain level. This > will ensure a better spread of tasks on idle CPUs. > > Running schbench on a hikey (8cores arm64) shows the problem: > > tip/sched/core : > schbench -m 2 -t 4 -s 1 -c 100 -r 10 > Latency percentiles (usec) > 50.0th: 33 > 75.0th: 45 > 90.0th: 51 > 95.0th: 4152 > *99.0th: 14288 > 99.5th: 14288 > 99.9th: 14288 > min=0, max=14276 > > tip/sched/core + patch : > schbench -m 2 -t 4 -s 1 -c 100 -r 10 > Latency percentiles (usec) > 50.0th: 34 > 75.0th: 47 > 90.0th: 52 > 95.0th: 78 > *99.0th: 94 > 99.5th: 94 > 99.9th: 94 > min=0, max=94 > > Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()") > Reported-by: Chris Mason > Suggested-by: Rik van Riel > Signed-off-by: Vincent Guittot Thanks!
Re: [PATCH] sched/fair: ensure tasks spreading in LLC during LB
On Mon, 2020-11-02 at 11:24 +0100, Vincent Guittot wrote: > Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()") > Reported-by: Chris Mason > Suggested-by: Rik van Riel > Signed-off-by: Vincent Guittot Tested-and-reviewed-by: Rik van Riel Thank you! -- All Rights Reversed. signature.asc Description: This is a digitally signed message part
[PATCH] sched/fair: ensure tasks spreading in LLC during LB
schbench shows latency increase for 95 percentile above since: commit 0b0695f2b34a ("sched/fair: Rework load_balance()") Align the behavior of the load balancer with the wake up path, which tries to select an idle CPU which belongs to the LLC for a waking task. calculate_imbalance() will use nr_running instead of the spare capacity when CPUs share resources (ie cache) at the domain level. This will ensure a better spread of tasks on idle CPUs. Running schbench on a hikey (8cores arm64) shows the problem: tip/sched/core : schbench -m 2 -t 4 -s 1 -c 100 -r 10 Latency percentiles (usec) 50.0th: 33 75.0th: 45 90.0th: 51 95.0th: 4152 *99.0th: 14288 99.5th: 14288 99.9th: 14288 min=0, max=14276 tip/sched/core + patch : schbench -m 2 -t 4 -s 1 -c 100 -r 10 Latency percentiles (usec) 50.0th: 34 75.0th: 47 90.0th: 52 95.0th: 78 *99.0th: 94 99.5th: 94 99.9th: 94 min=0, max=94 Fixes: 0b0695f2b34a ("sched/fair: Rework load_balance()") Reported-by: Chris Mason Suggested-by: Rik van Riel Signed-off-by: Vincent Guittot --- kernel/sched/fair.c | 3 ++- 1 file changed, 2 insertions(+), 1 deletion(-) diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c index aa4c6227cd6d..210b15f068a6 100644 --- a/kernel/sched/fair.c +++ b/kernel/sched/fair.c @@ -9031,7 +9031,8 @@ static inline void calculate_imbalance(struct lb_env *env, struct sd_lb_stats *s * emptying busiest. */ if (local->group_type == group_has_spare) { - if (busiest->group_type > group_fully_busy) { + if ((busiest->group_type > group_fully_busy) && + !(env->sd->flags & SD_SHARE_PKG_RESOURCES)) { /* * If busiest is overloaded, try to fill spare * capacity. This might end up creating spare capacity -- 2.17.1