linux-kernel - Re: [RFC PATCH v2 0/5] Idle Load Balance fixes and softirq enhancements

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Message-ID: <fdce27c2-ecf0-6c89-a372-3f93ce99ca61@amd.com>
Date: Wed, 4 Sep 2024 19:19:53 +0530
From: K Prateek Nayak <kprateek.nayak@....com>
To: Ingo Molnar <mingo@...hat.com>, Peter Zijlstra <peterz@...radead.org>,
	Juri Lelli <juri.lelli@...hat.com>, Vincent Guittot
	<vincent.guittot@...aro.org>, Dietmar Eggemann <dietmar.eggemann@....com>,
	Steven Rostedt <rostedt@...dmis.org>, Ben Segall <bsegall@...gle.com>, "Mel
 Gorman" <mgorman@...e.de>, Valentin Schneider <vschneid@...hat.com>, "Thomas
 Gleixner" <tglx@...utronix.de>
CC: Leonardo Bras <leobras@...hat.com>, "Paul E. McKenney"
	<paulmck@...nel.org>, Rik van Riel <riel@...riel.com>, Thorsten Blum
	<thorsten.blum@...lux.com>, Zqiang <qiang.zhang1211@...il.com>, Tejun Heo
	<tj@...nel.org>, Lai Jiangshan <jiangshanlai@...il.com>, Caleb Sander Mateos
	<csander@...estorage.com>, <linux-kernel@...r.kernel.org>, "Gautham R .
 Shenoy" <gautham.shenoy@....com>, Chen Yu <yu.c.chen@...el.com>, Julia Lawall
	<Julia.Lawall@...ia.fr>, Sebastian Andrzej Siewior <bigeasy@...utronix.de>
Subject: Re: [RFC PATCH v2 0/5] Idle Load Balance fixes and softirq
 enhancements

On 9/4/2024 4:42 PM, K Prateek Nayak wrote:
> Hello folks,
> 
> [..snip..]
> 
> Chenyu had reported a regression when running a modified version of
> ipistorm that performs a fixed set of IPIs between two CPUs on his
> setup with the whole v1 applied. I've benchmarked this series on both an
> AMD and an Intel system to catch any significant regression early.
> Following are the numbers from a dual socket Intel Ice Lake Xeon server
> (2 x 32C/64T) and 3rd Generation AMD EPYC system (2 x 64C/128T) running
> ipistorm between CPU8 and CPU16 (unless stated otherwise with *):
> 
> base: tip/master at commit 5566819aeba0 ("Merge branch into tip/master:
>        'x86/timers'") based on v6.11-rc6 + Patch from [1]

So that should have been the SM_IDLE fast path patch in [3]
https://lore.kernel.org/lkml/20240809092240.6921-1-kprateek.nayak@amd.com/

> 
>     ==================================================================
>     Test          : ipistorm (modified)
>     Units         : % improvement over base kernel
>     Interpretation: Higher is better
>     ======================= Intel Ice Lake Xeon ======================
>     kernel:					[pct imp]
>     performance gov, boost on			  -3%
>     powersave gov, boost on			  -2%
>     performance gov, boost off			  -3%
>     performance gov, boost off, cross node *	  -3%
>     ==================== 3rd Generation AMD EPYC =====================
>     kernel:					[pct imp]
>     performance gov, boost on, !PREEMPT_RT	  36%
>     performance gov, boost on,  PREEMPT_RT	  54%
>     ==================================================================

PREEMPT_RT kernel is based on:

     git.kernel.org/pub/scm/linux/kernel/git/rt/linux-rt-devel.git linux-6.11.y-rt-rebase

at commit 01ab72c93f63 ("Add localversion for -RT release") with the
addition of commit e68ac2b48849 ("softirq: Remove unused 'action'
parameter from action callback") from tip:irq/core and the SM_IDLE
fast-path patch from [3].

> 
> * cross node setup used CPU 16 on Node 0 and CPU 17 on Node 1 on the
>    dual socket Intel Ice Lake Xeon system.
> 
> Improvements on PREEMPT_RT can perhaps be attributed to cacheline
> aligning the per-cpu softirq_ctrl variable.
> 
> This series has been marked RFC since this is my first attempt at
> dealing with PREEMPT_RT nuances. Any and all feedback is appreciated.
> 
> [1] https://lore.kernel.org/lkml/20240710090210.41856-1-kprateek.nayak@amd.com/
> [2] https://lore.kernel.org/lkml/fcf823f-195e-6c9a-eac3-25f870cb35ac@inria.fr/
> [3] https://lore.kernel.org/lkml/20240809092240.6921-1-kprateek.nayak@amd.com/
> [4] https://lore.kernel.org/lkml/225e6d74-ed43-51dd-d1aa-c75c86dd58eb@amd.com/
> [5] https://lore.kernel.org/lkml/20240710150557.GB27299@noisy.programming.kicks-ass.net/
> ---
> [..snip..]
> 

-- 
Thanks and Regards,
Prateek