linux-kernel - Re: [PATCH v1] sched/uclamp: Exclude kernel threads from uclamp logic

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Message-ID: <20250710100311.15cc55ce@batman.local.home>
Date: Thu, 10 Jul 2025 10:03:11 -0400
From: Steven Rostedt <rostedt@...dmis.org>
To: Zihuan Zhang <zhangzihuan@...inos.cn>
Cc: Christian Loehle <christian.loehle@....com>, xuewen.yan@...soc.com,
 vincent.guittot@...aro.org, mingo@...hat.com, peterz@...radead.org,
 juri.lelli@...hat.com, bsegall@...gle.com, mgorman@...e.de,
 vschneid@...hat.com, hongyan.xia2@....com, linux-kernel@...r.kernel.org,
 ke.wang@...soc.com, di.shen@...soc.com, xuewen.yan94@...il.com,
 kprateek.nayak@....com, kuyo.chang@...iatek.com, juju.sung@...iatek.com,
 qyousef@...alina.io
Subject: Re: [PATCH v1] sched/uclamp: Exclude kernel threads from uclamp
 logic

On Thu, 10 Jul 2025 08:55:28 +0800
Zihuan Zhang <zhangzihuan@...inos.cn> wrote:

> The motivation behind this patch is to explore whether it’s worth 
> optimizing the uclamp hot path a bit further. Since kernel threads 
> typically don’t benefit from uclamp adjustments and often just inherit 
> default values (e.g., max=1024), we were wondering if skipping the 
> aggregation logic for such cases could slightly reduce overhead in some 
> workloads.
> 
> Of course, we want to be conservative and avoid breaking any legitimate 
> usage. So I’d love to hear your opinion — do you think it’s worthwhile 
> to pursue this kind of micro-optimization in uclamp, or is the potential 
> gain too marginal to justify the added logic?

My honest opinion is that if there's not a huge issue you are trying
to solve, then it's best to leave things as is. Tweaking this for
micro-optimizations usually end up causing a regression somewhere you
never expected.

-- Steve