Re: [PATCH v2 00/12] sched: Address schbench regression

[Beata Michalska <beata.michalska@arm.com>]

On Thu, Jul 17, 2025 at 03:04:55PM +0200, Beata Michalska wrote:
> Hi Peter,
> 
> Below are the results of running the schbench on Altra
> (as a reminder 2-core MC, 2 Numa Nodes, 160 cores)
> 
> `Legend:
> - 'Flags=none' means neither TTWU_QUEUE_DEFAULT nor
>   TTWU_QUEUE_DELAYED is set (or available).
> - '*…*' marks Top-3 Min & Max, Bottom-3 Std dev, and
>   Top-3 90th-percentile values.
> 
> Base 6.16-rc5
>   Flags=none
>   Min=681870.77 | Max=913649.50 | Std=53802.90       | 90th=890201.05
> 
> sched/fair: bump sd->max_newidle_lb_cost when newidle balance fails
>   Flags=none
>   Min=770952.12 | Max=888047.45 | Std=34430.24       | 90th=877347.24
> 
> sched/psi: Optimize psi_group_change() cpu_clock() usage
>   Flags=none
>   Min=748137.65 | Max=936312.33 | Std=56818.23       | 90th=*921497.27*
> 
> sched/deadline: Less agressive dl_server handling
>   Flags=none
>   Min=783621.95 | Max=*944604.67* | Std=43538.64     | 90th=*909961.16*
> 
> sched: Optimize ttwu() / select_task_rq()
>   Flags=none
>   Min=*826038.87* | Max=*1003496.73* | Std=49875.43  | 90th=*971944.88*
> 
> sched: Use lock guard in ttwu_runnable()
>   Flags=none
>   Min=780172.75 | Max=914170.20 | Std=35998.33       | 90th=866095.80
> 
> sched: Add ttwu_queue controls
>   Flags=TTWU_QUEUE_DEFAULT
>   Min=*792430.45* | Max=903422.78 | Std=33582.71     | 90th=887256.68
> 
>   Flags=none
>   Min=*803532.80* | Max=894772.48 | Std=29359.35     | 90th=877920.34
> 
> sched: Introduce ttwu_do_migrate()
>   Flags=TTWU_QUEUE_DEFAULT
>   Min=749824.30 | Max=*965139.77* | Std=57022.47     | 90th=903659.07
>  
>   Flags=none
>   Min=787464.65 | Max=885349.20 | Std=27030.82       | 90th=875750.44
> 
> psi: Split psi_ttwu_dequeue()
>   Flags=TTWU_QUEUE_DEFAULT
>   Min=762960.98 | Max=916538.12 | Std=42002.19       | 90th=876425.84
>  
>   Flags=none
>   Min=773608.48 | Max=920812.87 | Std=42189.17       | 90th=871760.47
> 
> sched: Re-arrange __ttwu_queue_wakelist()
>   Flags=TTWU_QUEUE_DEFAULT
>   Min=702870.58 | Max=835243.42 | Std=44224.02       | 90th=825311.12
> 
>   Flags=none
>   Min=712499.38 | Max=838492.03 | Std=38351.20       | 90th=817135.94
> 
> sched: Use lock guard in sched_ttwu_pending()
>   Flags=TTWU_QUEUE_DEFAULT
>   Min=729080.55 | Max=853609.62 | Std=43440.63       | 90th=838684.48
> 
>   Flags=none
>   Min=708123.47 | Max=850804.48 | Std=40642.28       | 90th=830295.08
> 
> sched: Change ttwu_runnable() vs sched_delayed
>   Flags=TTWU_QUEUE_DEFAULT
>   Min=580218.87 | Max=838684.07 | Std=57078.24       | 90th=792973.33
> 
>   Flags=none
>   Min=721274.90 | Max=784897.92 | Std=*19017.78*     | 90th=774792.30
> 
> sched: Add ttwu_queue support for delayed tasks
>   Flags=none
>   Min=712979.48 | Max=830192.10 | Std=33173.90       | 90th=798599.66
> 
>   Flags=TTWU_QUEUE_DEFAULT
>   Min=698094.12 | Max=857627.93 | Std=38294.94       | 90th=789981.59
>  
>   Flags=TTWU_QUEUE_DEFAULT/TTWU_QUEUE_DELAYED
>   Min=683348.77 | Max=782179.15 | Std=25086.71       | 90th=750947.00
> 
>   Flags=TTWU_QUEUE_DELAYED
>   Min=669822.23 | Max=807768.85 | Std=38766.41       | 90th=794052.05
> 
> sched: fix ttwu_delayed
This one is actually:
sched: Add ttwu_queue support for delayed tasks
+
https://lore.kernel.org/all/0672c7df-543c-4f3e-829a-46969fad6b34@amd.com/

Apologies for that.

---
BR
Beata
>   Flags=none
>   Min=671844.35 | Max=798737.67 | Std=33438.64       | 90th=788584.62
> 
>   Flags=TTWU_QUEUE_DEFAULT
>   Min=688607.40 | Max=828679.53 | Std=33184.78       | 90th=782490.23
> 
>   Flags=TTWU_QUEUE_DEFAULT/TTWU_QUEUE_DELAYED
>   Min=579171.13 | Max=643929.18 | Std=*14644.92*     | 90th=639764.16
> 
>   Flags=TTWU_QUEUE_DELAYED
>   Min=614265.22 | Max=675172.05 | Std=*13309.92*     | 90th=647181.10
> 
> 
> Best overall performer:
> sched: Optimize ttwu() / select_task_rq()
>   Flags=none
>   Min=*826038.87* | Max=*1003496.73* | Std=49875.43 | 90th=*971944.88*
> 
> Hope this will he somehwat helpful.
> 
> ---
> BR
> Beata
> 
> On Wed, Jul 02, 2025 at 01:49:24PM +0200, Peter Zijlstra wrote:
> > Hi!
> > 
> > Previous version:
> > 
> >   https://lkml.kernel.org/r/20250520094538.086709102@infradead.org
> > 
> > 
> > Changes:
> >  - keep dl_server_stop(), just remove the 'normal' usage of it (juril)
> >  - have the sched_delayed wake list IPIs do select_task_rq() (vingu)
> >  - fixed lockdep splat (dietmar)
> >  - added a few preperatory patches
> > 
> > 
> > Patches apply on top of tip/master (which includes the disabling of private futex)
> > and clm's newidle balance patch (which I'm awaiting vingu's ack on).
> > 
> > Performance is similar to the last version; as tested on my SPR on v6.15 base:
> > 
> > v6.15:
> > schbench-6.15.0-1.txt:average rps: 2891403.72
> > schbench-6.15.0-2.txt:average rps: 2889997.02
> > schbench-6.15.0-3.txt:average rps: 2894745.17
> > 
> > v6.15 + patches 1-10:
> > schbench-6.15.0-dirty-4.txt:average rps: 3038265.95
> > schbench-6.15.0-dirty-5.txt:average rps: 3037327.50
> > schbench-6.15.0-dirty-6.txt:average rps: 3038160.15
> > 
> > v6.15 + all patches:
> > schbench-6.15.0-dirty-deferred-1.txt:average rps: 3043404.30
> > schbench-6.15.0-dirty-deferred-2.txt:average rps: 3046124.17
> > schbench-6.15.0-dirty-deferred-3.txt:average rps: 3043627.10
> > 
> > 
> > Patches can also be had here:
> > 
> >   git://git.kernel.org/pub/scm/linux/kernel/git/peterz/queue.git sched/core
> > 
> > 
> > I'm hoping we can get this merged for next cycle so we can all move on from this.
> > 
> > 
>