From: Peter Zijlstra <peterz@infradead.org>
To: Mario Roy <marioeroy@gmail.com>
Cc: Chris Mason <clm@meta.com>,
Joseph Salisbury <joseph.salisbury@oracle.com>,
Adam Li <adamli@os.amperecomputing.com>,
Hazem Mohamed Abuelfotoh <abuehaze@amazon.com>,
Josh Don <joshdon@google.com>,
mingo@redhat.com, juri.lelli@redhat.com,
vincent.guittot@linaro.org, dietmar.eggemann@arm.com,
rostedt@goodmis.org, bsegall@google.com, mgorman@suse.de,
vschneid@redhat.com, linux-kernel@vger.kernel.org,
kprateek.nayak@amd.com
Subject: Re: [PATCH 4/4] sched/fair: Proportional newidle balance
Date: Tue, 27 Jan 2026 11:40:41 +0100 [thread overview]
Message-ID: <20260127104041.GD217302@noisy.programming.kicks-ass.net> (raw)
In-Reply-To: <20260123110306.GA217302@noisy.programming.kicks-ass.net>
On Fri, Jan 23, 2026 at 12:03:06PM +0100, Peter Zijlstra wrote:
> On Fri, Jan 23, 2026 at 11:50:46AM +0100, Peter Zijlstra wrote:
> > On Sun, Jan 18, 2026 at 03:46:22PM -0500, Mario Roy wrote:
> > > The patch "Proportional newidle balance" introduced a regression
> > > with Linux 6.12.65 and 6.18.5. There is noticeable regression with
> > > easyWave testing. [1]
> > >
> > > The CPU is AMD Threadripper 9960X CPU (24/48). I followed the source
> > > to install easyWave [2]. That is fetching the two tar.gz archives.
> >
> > What is the actual configuration of that chip? Is it like 3*8 or 4*6
> > (CCX wise). A quick google couldn't find me the answer :/
>
> Obviously I found it right after sending this. It's a 4x6 config.
> Meaning it needs newidle to balance between those 4 domains.
So with the below patch on top of my Xeon w7-2495X (which is 24-core
48-thread) I too have 4 LLC :-)
And I think I can see a slight difference, but nowhere near as terrible.
Let me go stick some tracing on.
cpu0 0 0 0 0 0 0 199480591279 9327118209 21136
domain0 SMT 0000,01000001 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain1 MC 1111,11111111 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain2 PKG ffff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
cpu1 0 0 0 0 0 0 205007928818 2654503460 14772
domain0 SMT 0000,02000002 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain1 MC 2222,22222222 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain2 PKG ffff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
cpu2 0 0 0 0 0 0 190458000839 2361863044 13265
domain0 SMT 0000,04000004 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain1 MC 4444,44444444 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain2 PKG ffff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
cpu3 0 0 0 0 0 0 193040171114 2769182152 16215
domain0 SMT 0000,08000008 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain1 MC 8888,88888888 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
domain2 PKG ffff,ffffffff 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0 0
...
easywave# echo NI_RANDOM > /debug/sched/features; OMP_NUM_THREADS=48 ./src/easywave -grid examples/e2Asean.grd -source examples/BengkuluSept2007.flt -time 300
easyWave ver.2013-04-11
Model time = 00:00:00, elapsed: 2 msec
Model time = 00:10:00, elapsed: 6 msec
Model time = 00:20:00, elapsed: 13 msec
Model time = 00:30:00, elapsed: 21 msec
Model time = 00:40:00, elapsed: 33 msec
Model time = 00:50:00, elapsed: 59 msec
Model time = 01:00:00, elapsed: 136 msec
Model time = 01:10:00, elapsed: 160 msec
Model time = 01:20:00, elapsed: 189 msec
Model time = 01:30:00, elapsed: 266 msec
Model time = 01:40:00, elapsed: 321 msec
Model time = 01:50:00, elapsed: 401 msec
Model time = 02:00:00, elapsed: 482 msec
Model time = 02:10:00, elapsed: 619 msec
Model time = 02:20:00, elapsed: 731 msec
Model time = 02:30:00, elapsed: 856 msec
Model time = 02:40:00, elapsed: 1013 msec
Model time = 02:50:00, elapsed: 1204 msec
Model time = 03:00:00, elapsed: 1437 msec
Model time = 03:10:00, elapsed: 1715 msec
Model time = 03:20:00, elapsed: 1952 msec
Model time = 03:30:00, elapsed: 2713 msec
Model time = 03:40:00, elapsed: 3090 msec
Model time = 03:50:00, elapsed: 3644 msec
Model time = 04:00:00, elapsed: 4157 msec
Model time = 04:10:00, elapsed: 4632 msec
Model time = 04:20:00, elapsed: 5131 msec
Model time = 04:30:00, elapsed: 5685 msec
Model time = 04:40:00, elapsed: 6404 msec
Model time = 04:50:00, elapsed: 7154 msec
Model time = 05:00:00, elapsed: 8143 msec
easywave# echo NO_NI_RANDOM > /debug/sched/features; OMP_NUM_THREADS=48 ./src/easywave -grid examples/e2Asean.grd -source examples/BengkuluSept2007.flt -time 300
easyWave ver.2013-04-11
Model time = 00:00:00, elapsed: 1 msec
Model time = 00:10:00, elapsed: 6 msec
Model time = 00:20:00, elapsed: 12 msec
Model time = 00:30:00, elapsed: 21 msec
Model time = 00:40:00, elapsed: 33 msec
Model time = 00:50:00, elapsed: 94 msec
Model time = 01:00:00, elapsed: 114 msec
Model time = 01:10:00, elapsed: 138 msec
Model time = 01:20:00, elapsed: 191 msec
Model time = 01:30:00, elapsed: 227 msec
Model time = 01:40:00, elapsed: 272 msec
Model time = 01:50:00, elapsed: 322 msec
Model time = 02:00:00, elapsed: 381 msec
Model time = 02:10:00, elapsed: 458 msec
Model time = 02:20:00, elapsed: 634 msec
Model time = 02:30:00, elapsed: 861 msec
Model time = 02:40:00, elapsed: 1050 msec
Model time = 02:50:00, elapsed: 1265 msec
Model time = 03:00:00, elapsed: 1463 msec
Model time = 03:10:00, elapsed: 1658 msec
Model time = 03:20:00, elapsed: 1892 msec
Model time = 03:30:00, elapsed: 2243 msec
Model time = 03:40:00, elapsed: 2672 msec
Model time = 03:50:00, elapsed: 3038 msec
Model time = 04:00:00, elapsed: 3462 msec
Model time = 04:10:00, elapsed: 3961 msec
Model time = 04:20:00, elapsed: 4455 msec
Model time = 04:30:00, elapsed: 5040 msec
Model time = 04:40:00, elapsed: 5594 msec
Model time = 04:50:00, elapsed: 6190 msec
Model time = 05:00:00, elapsed: 7065 msec
---
diff --git a/arch/x86/include/asm/processor.h b/arch/x86/include/asm/processor.h
index a24c7805acdb..d0d7cefb6cd3 100644
--- a/arch/x86/include/asm/processor.h
+++ b/arch/x86/include/asm/processor.h
@@ -699,6 +699,11 @@ static inline u32 per_cpu_l2c_id(unsigned int cpu)
return per_cpu(cpu_info.topo.l2c_id, cpu);
}
+static inline u32 per_cpu_core_id(unsigned int cpu)
+{
+ return per_cpu(cpu_info.topo.core_id, cpu);
+}
+
#ifdef CONFIG_CPU_SUP_AMD
/*
* Issue a DIV 0/1 insn to clear any division data from previous DIV
diff --git a/arch/x86/kernel/smpboot.c b/arch/x86/kernel/smpboot.c
index 5cd6950ab672..5e7349c0f6ed 100644
--- a/arch/x86/kernel/smpboot.c
+++ b/arch/x86/kernel/smpboot.c
@@ -438,6 +438,9 @@ static bool match_llc(struct cpuinfo_x86 *c, struct cpuinfo_x86 *o)
if (per_cpu_llc_id(cpu1) != per_cpu_llc_id(cpu2))
return false;
+ if ((per_cpu_core_id(cpu1) % 4) != (per_cpu_core_id(cpu2) % 4))
+ return false;
+
/*
* Allow the SNC topology without warning. Return of false
* means 'c' does not share the LLC of 'o'. This will be
next prev parent reply other threads:[~2026-01-27 10:40 UTC|newest]
Thread overview: 69+ messages / expand[flat|nested] mbox.gz Atom feed top
2025-11-07 16:06 [PATCH 0/4] sched: The newidle balance regression Peter Zijlstra
2025-11-07 16:06 ` [PATCH 1/4] sched/fair: Revert max_newidle_lb_cost bump Peter Zijlstra
2025-11-14 12:19 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2025-11-17 16:23 ` tip-bot2 for Peter Zijlstra
2025-11-07 16:06 ` [PATCH 2/4] sched/fair: Small cleanup to sched_balance_newidle() Peter Zijlstra
2025-11-10 13:55 ` Dietmar Eggemann
2025-11-10 14:04 ` Peter Zijlstra
2025-11-12 14:37 ` Shrikanth Hegde
2025-11-12 14:42 ` Peter Zijlstra
2025-11-12 15:08 ` Peter Zijlstra
2025-11-12 15:28 ` Shrikanth Hegde
2025-11-14 9:49 ` Peter Zijlstra
2025-11-14 10:22 ` Vincent Guittot
2025-11-14 11:05 ` Peter Zijlstra
2025-11-14 13:11 ` Vincent Guittot
2025-11-14 12:19 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2025-11-17 16:23 ` tip-bot2 for Peter Zijlstra
2025-11-07 16:06 ` [PATCH 3/4] sched/fair: Small cleanup to update_newidle_cost() Peter Zijlstra
2025-11-14 12:19 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2025-11-17 16:23 ` tip-bot2 for Peter Zijlstra
2025-11-07 16:06 ` [PATCH 4/4] sched/fair: Proportional newidle balance Peter Zijlstra
2025-11-10 13:55 ` Dietmar Eggemann
2025-11-11 9:07 ` Adam Li
2025-11-11 9:20 ` Peter Zijlstra
2025-11-12 12:04 ` Adam Li
2025-11-12 13:41 ` Peter Zijlstra
2025-11-12 15:42 ` Shrikanth Hegde
2025-11-14 9:35 ` Peter Zijlstra
2025-11-14 12:18 ` [tip: sched/core] " tip-bot2 for Peter Zijlstra
2025-11-17 16:23 ` tip-bot2 for Peter Zijlstra
2026-01-18 20:46 ` [PATCH 4/4] " Mario Roy
2026-01-23 10:50 ` Peter Zijlstra
2026-01-23 11:03 ` Peter Zijlstra
2026-01-23 12:24 ` K Prateek Nayak
2026-01-28 4:08 ` K Prateek Nayak
2026-01-27 4:15 ` Mario Roy
2026-01-27 10:40 ` Peter Zijlstra [this message]
2026-01-27 15:17 ` Peter Zijlstra
2026-01-30 1:44 ` Mario Roy
2026-01-30 4:14 ` Mario Roy
2026-02-24 9:13 ` [tip: sched/core] sched/fair: More complex proportional " tip-bot2 for Peter Zijlstra
2026-01-25 12:22 ` [PATCH 4/4] sched/fair: Proportional " Mohamed Abuelfotoh, Hazem
2026-01-27 8:44 ` Peter Zijlstra
2026-01-28 15:48 ` Mohamed Abuelfotoh, Hazem
2026-01-29 9:19 ` Peter Zijlstra
2026-01-29 9:24 ` Peter Zijlstra
2026-01-30 16:12 ` Mohamed Abuelfotoh, Hazem
2026-01-30 13:16 ` Mohamed Abuelfotoh, Hazem
2026-02-02 10:51 ` Peter Zijlstra
2026-02-02 11:07 ` Mohamed Abuelfotoh, Hazem
2026-02-04 12:45 ` Mohamed Abuelfotoh, Hazem
2026-02-04 13:27 ` Peter Zijlstra
2026-02-04 13:59 ` Mohamed Abuelfotoh, Hazem
2026-02-04 14:05 ` Peter Zijlstra
2026-02-04 22:48 ` Mohamed Abuelfotoh, Hazem
2026-01-27 8:50 ` Peter Zijlstra
2026-01-27 9:13 ` Peter Zijlstra
2026-01-28 16:24 ` Mohamed Abuelfotoh, Hazem
2026-01-28 16:03 ` Mohamed Abuelfotoh, Hazem
2026-04-29 8:51 ` Qing Wang
2026-05-06 2:44 ` [PATCH] sched/fair: Replace random newidle_balance with Bresenham accumulator Qing Wang
2026-05-13 2:21 ` Qing Wang
2026-05-13 5:29 ` K Prateek Nayak
2026-05-14 2:22 ` Qing Wang
2026-06-02 5:46 ` [PATCH v2] " Qing Wang
2025-11-10 19:47 ` [PATCH 0/4] sched: The newidle balance regression Chris Mason
2025-11-11 19:08 ` Josh Don
2025-11-12 21:59 ` Chris Mason
2025-11-14 9:37 ` Peter Zijlstra
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20260127104041.GD217302@noisy.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=abuehaze@amazon.com \
--cc=adamli@os.amperecomputing.com \
--cc=bsegall@google.com \
--cc=clm@meta.com \
--cc=dietmar.eggemann@arm.com \
--cc=joseph.salisbury@oracle.com \
--cc=joshdon@google.com \
--cc=juri.lelli@redhat.com \
--cc=kprateek.nayak@amd.com \
--cc=linux-kernel@vger.kernel.org \
--cc=marioeroy@gmail.com \
--cc=mgorman@suse.de \
--cc=mingo@redhat.com \
--cc=rostedt@goodmis.org \
--cc=vincent.guittot@linaro.org \
--cc=vschneid@redhat.com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is an external index of several public inboxes,
see mirroring instructions on how to clone and mirror
all data and code used by this external index.