Re: [PATCH] sched/fair: Preserve PLACE_DEADLINE_INITIAL deadline

From: K Prateek Nayak
Date: Thu Oct 05 2023 - 10:36:04 EST

Hello Daniel,

On 10/4/2023 6:47 AM, Daniel Jordan wrote:
> An entity is supposed to get an earlier deadline with
> PLACE_DEADLINE_INITIAL when it's forked, but the deadline gets
> overwritten soon after in enqueue_entity() the first time a forked
> entity is woken so that PLACE_DEADLINE_INITIAL is effectively a no-op.
>
> Placing in task_fork_fair() seems unnecessary since none of the values
> that get set (slice, vruntime, deadline) are used before they're set
> again at enqueue time, so get rid of that and just pass ENQUEUE_INITIAL
> to enqueue_entity() via wake_up_new_task().
>
> Fixes: e8f331bcc270 ("sched/smp: Use lag to simplify cross-runqueue placement")
> Signed-off-by: Daniel Jordan <daniel.m.jordan@xxxxxxxxxx>

I got a chance to this this on a 3rd Generation EPYC system. I don't
see anything out of the ordinary except for a small regression on
hackbench. I'll leave the full result below.

o System details

- 3rd Generation EPYC System
- 2 sockets each with 64C/128T
- NPS1 (Each socket is a NUMA node)
- Boost enabled, C2 Disabled (POLL and MWAIT based C1 remained enabled)


o Kernel Details

- tip: tip:sched/core at commit d4d6596b4386 ("sched/headers: Remove
duplicate header inclusions")

- place-deadline-fix: tip + this patch


o Benchmark Results

==================================================================
Test : hackbench
Units : Normalized time in seconds
Interpretation: Lower is better
Statistic : AMean
==================================================================
Case: tip[pct imp](CV) place-deadline-fix[pct imp](CV)
1-groups 1.00 [ -0.00]( 2.58) 1.04 [ -3.63]( 3.14)
2-groups 1.00 [ -0.00]( 1.87) 1.03 [ -2.98]( 1.85)
4-groups 1.00 [ -0.00]( 1.63) 1.02 [ -2.35]( 1.59)
8-groups 1.00 [ -0.00]( 1.38) 1.03 [ -2.92]( 1.20)
16-groups 1.00 [ -0.00]( 2.67) 1.02 [ -1.61]( 2.08)


==================================================================
Test : tbench
Units : Normalized throughput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Clients: tip[pct imp](CV) place-deadline-fix[pct imp](CV)
1 1.00 [ 0.00]( 0.59) 1.02 [ 2.09]( 0.07)
2 1.00 [ 0.00]( 1.19) 1.02 [ 2.38]( 0.82)
4 1.00 [ 0.00]( 0.33) 1.03 [ 2.89]( 0.99)
8 1.00 [ 0.00]( 0.76) 1.02 [ 2.10]( 0.46)
16 1.00 [ 0.00]( 1.10) 1.01 [ 0.81]( 0.49)
32 1.00 [ 0.00]( 1.47) 1.02 [ 1.77]( 0.58)
64 1.00 [ 0.00]( 1.77) 1.02 [ 1.83]( 1.77)
128 1.00 [ 0.00]( 0.41) 1.02 [ 2.49]( 0.52)
256 1.00 [ 0.00]( 0.63) 1.03 [ 3.03]( 1.38)
512 1.00 [ 0.00]( 0.32) 1.02 [ 1.61]( 0.45)
1024 1.00 [ 0.00]( 0.22) 1.01 [ 1.00]( 0.26)


==================================================================
Test : stream-10
Units : Normalized Bandwidth, MB/s
Interpretation: Higher is better
Statistic : HMean
==================================================================
Test: tip[pct imp](CV) place-deadline-fix[pct imp](CV)
Copy 1.00 [ 0.00]( 9.30) 0.85 [-15.36](11.26)
Scale 1.00 [ 0.00]( 6.67) 0.98 [ -2.36]( 7.53)
Add 1.00 [ 0.00]( 6.77) 0.92 [ -7.86]( 7.83)
Triad 1.00 [ 0.00]( 7.36) 0.94 [ -5.57]( 6.82)


==================================================================
Test : stream-100
Units : Normalized Bandwidth, MB/s
Interpretation: Higher is better
Statistic : HMean
==================================================================
Test: tip[pct imp](CV) place-deadline-fix[pct imp](CV)
Copy 1.00 [ 0.00]( 1.83) 0.96 [ -3.68]( 5.08)
Scale 1.00 [ 0.00]( 6.41) 1.03 [ 2.66]( 5.28)
Add 1.00 [ 0.00]( 6.23) 1.02 [ 1.54]( 4.97)
Triad 1.00 [ 0.00]( 0.89) 0.94 [ -5.68]( 6.78)


==================================================================
Test : netperf
Units : Normalized Througput
Interpretation: Higher is better
Statistic : AMean
==================================================================
Clients: tip[pct imp](CV) place-deadline-fix[pct imp](CV)
1-clients 1.00 [ 0.00]( 0.05) 1.02 [ 1.83]( 1.98)
2-clients 1.00 [ 0.00]( 0.93) 1.02 [ 1.87]( 2.45)
4-clients 1.00 [ 0.00]( 0.54) 1.02 [ 2.19]( 1.99)
8-clients 1.00 [ 0.00]( 0.48) 1.02 [ 2.29]( 2.27)
16-clients 1.00 [ 0.00]( 0.42) 1.02 [ 1.60]( 1.70)
32-clients 1.00 [ 0.00]( 0.78) 1.02 [ 1.88]( 2.08)
64-clients 1.00 [ 0.00]( 1.45) 1.02 [ 2.33]( 2.18)
128-clients 1.00 [ 0.00]( 0.97) 1.02 [ 2.38]( 1.95)
256-clients 1.00 [ 0.00]( 4.57) 1.02 [ 2.50]( 5.42)
512-clients 1.00 [ 0.00](52.74) 1.03 [ 3.38](49.69)


==================================================================
Test : schbench
Units : Normalized 99th percentile latency in us
Interpretation: Lower is better
Statistic : Median
==================================================================
#workers: tip[pct imp](CV) place-deadline-fix[pct imp](CV)
1 1.00 [ -0.00]( 3.95) 0.90 [ 10.26](31.80)
2 1.00 [ -0.00](10.45) 1.08 [ -7.89](15.33)
4 1.00 [ -0.00]( 4.76) 0.93 [ 7.14]( 3.95)
8 1.00 [ -0.00]( 9.35) 1.06 [ -6.25]( 8.90)
16 1.00 [ -0.00]( 8.84) 0.92 [ 8.06]( 4.39)
32 1.00 [ -0.00]( 3.33) 1.04 [ -4.40]( 3.68)
64 1.00 [ -0.00]( 6.70) 0.96 [ 4.17]( 2.75)
128 1.00 [ -0.00]( 0.71) 0.96 [ 3.55]( 1.26)
256 1.00 [ -0.00](31.20) 1.28 [-28.21]( 9.69)
512 1.00 [ -0.00]( 4.98) 1.00 [ 0.48]( 2.76)


==================================================================
Test : ycsb-cassandra
Units : Normalized throughput
Interpretation: Higher is better
Statistic : Mean
==================================================================
Metric tip place-deadline-fix(pct imp)
Throughput 1.00 1.01 (%diff: 1.06%)


==================================================================
Test : ycsb-mondodb
Units : Normalized throughput
Interpretation: Higher is better
Statistic : Mean
==================================================================
Metric tip place-deadline-fix(pct imp)
Throughput 1.00 1.00 (%diff: 0.25%)


==================================================================
Test : DeathStarBench
Units : Normalized throughput
Interpretation: Higher is better
Statistic : Mean
==================================================================
Pinning scaling tip place-deadline-fix(pct imp)
1CCD 1 1.00 1.00 (%diff: -0.32%)
2CCD 2 1.00 1.00 (%diff: -0.26%)
4CCD 4 1.00 1.00 (%diff: 0.17%)
8CCD 8 1.00 1.00 (%diff: -0.17%)


--
I see there is a v2. I'll give that a spin as well.

> ---
>
> Tested on top of peterz/sched/eevdf from 2023-10-03.
>
> kernel/sched/core.c | 2 +-
> kernel/sched/fair.c | 1 -
> 2 files changed, 1 insertion(+), 2 deletions(-)
>
> diff --git a/kernel/sched/core.c b/kernel/sched/core.c
> index 779cdc7969c81..500e2dbfd41dd 100644
> --- a/kernel/sched/core.c
> +++ b/kernel/sched/core.c
> @@ -4854,7 +4854,7 @@ void wake_up_new_task(struct task_struct *p)
> update_rq_clock(rq);
> post_init_entity_util_avg(p);
>
> - activate_task(rq, p, ENQUEUE_NOCLOCK);
> + activate_task(rq, p, ENQUEUE_INITIAL | ENQUEUE_NOCLOCK);
> trace_sched_wakeup_new(p);
> wakeup_preempt(rq, p, WF_FORK);
> #ifdef CONFIG_SMP
> diff --git a/kernel/sched/fair.c b/kernel/sched/fair.c
> index a0b4dac2662c9..5872b8a3f5891 100644
> --- a/kernel/sched/fair.c
> +++ b/kernel/sched/fair.c
> @@ -12446,7 +12446,6 @@ static void task_fork_fair(struct task_struct *p)
> curr = cfs_rq->curr;
> if (curr)
> update_curr(cfs_rq);
> - place_entity(cfs_rq, se, ENQUEUE_INITIAL);
> rq_unlock(rq, &rf);
> }
>

--
Thanks and Regards,
Prateek