linux-kernel - Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice

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Message-ID: <20250201115906.GB8256@noisy.programming.kicks-ass.net>
Date: Sat, 1 Feb 2025 12:59:06 +0100
From: Peter Zijlstra <peterz@...radead.org>
To: Steven Rostedt <rostedt@...dmis.org>
Cc: linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>,
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	broonie@...il.com
Subject: Re: [RFC][PATCH 1/2] sched: Extended scheduler time slice

On Fri, Jan 31, 2025 at 05:58:38PM -0500, Steven Rostedt wrote:
> From: "Steven Rostedt (Google)" <rostedt@...dmis.org>
> 
> This is to improve user space implemented spin locks or any critical
> section. It may also be extended for VMs and their guest spin locks as
> well, but that will come later.
> 
> This adds a new field in the struct rseq called cr_counter. This is a 32 bit
> field where bit zero is a flag reserved for the kernel, and the other 31
> bits can be used as a counter (although the kernel doesn't care how they
> are used, as any bit set means the same).
> 
> This works in tandem with PREEMPT_LAZY, where a task can tell the kernel
> via the rseq structure that it is in a critical section (like holding a
> spin lock) that it will be leaving very shortly, and to ask the kernel to
> not preempt it at the moment.

I still have full hate for this approach.