linux-kernel - Re: [PATCH 00/17] Paravirt CPUs and push task for less vCPU preemption

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Message-ID: <aUBHw7MvOQYusuuA@yury>
Date: Mon, 15 Dec 2025 12:39:15 -0500
From: Yury Norov <yury.norov@...il.com>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>
Cc: Ilya Leoshkevich <iii@...ux.ibm.com>, linux-kernel@...r.kernel.org,
	linuxppc-dev@...ts.ozlabs.org, mingo@...hat.com,
	peterz@...radead.org, juri.lelli@...hat.com,
	vincent.guittot@...aro.org, tglx@...utronix.de, maddy@...ux.ibm.com,
	srikar@...ux.ibm.com, gregkh@...uxfoundation.org,
	pbonzini@...hat.com, seanjc@...gle.com, kprateek.nayak@....com,
	vschneid@...hat.com, huschle@...ux.ibm.com, rostedt@...dmis.org,
	dietmar.eggemann@....com, christophe.leroy@...roup.eu,
	linux-s390@...r.kernel.org
Subject: Re: [PATCH 00/17] Paravirt CPUs and push task for less vCPU
 preemption

On Fri, Dec 05, 2025 at 11:00:18AM +0530, Shrikanth Hegde wrote:
> 
> 
> On 12/4/25 6:58 PM, Ilya Leoshkevich wrote:
> > On Wed, 2025-11-19 at 18:14 +0530, Shrikanth Hegde wrote:

...

> > Others have already commented on the naming, and I would agree that
> > "paravirt" is really misleading. I cannot say that the previous "cpu-
> > avoid" one was perfect, but it was much better.

It was my suggestion to switch names. cpu-avoid is definitely a
no-go. Because it doesn't explain anything and only confuses.

I suggested 'paravirt' (notice - only suggested) because the patch
series is mainly discussing paravirtualized VMs. But now I'm not even
sure that the idea of the series is:

1. Applicable only to paravirtualized VMs; and 
2. Preemption and rescheduling throttling requires another in-kernel
   concept other than nohs, isolcpus, cgroups and similar.

Shrikanth, can you please clarify the scope of the new feature? Would
it be useful for non-paravirtualized VMs, for example? Any other
task-cpu bonding problems?

On previous rounds you tried to implement the same with cgroups, as
far as I understood. Can you discuss that? What exactly can't be done
with the existing kernel APIs?

Thanks,
Yury

> > [1] https://github.com/iii-i/linux/commits/iii/poc/cpu-avoid/v3/
> 
> Will look into it. one thing to to be careful are CPU numbers.