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

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Message-ID: <0f53d5b8-dbb7-4265-940a-2f2be3d0154d@kernel.org>
Date: Tue, 25 Nov 2025 08:48:48 +0100
From: "Christophe Leroy (CS GROUP)" <chleroy@...nel.org>
To: Shrikanth Hegde <sshegde@...ux.ibm.com>,
 Greg KH <gregkh@...uxfoundation.org>
Cc: 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, yury.norov@...il.com,
 maddy@...ux.ibm.com, srikar@...ux.ibm.com, pbonzini@...hat.com,
 seanjc@...gle.com, kprateek.nayak@....com, vschneid@...hat.com,
 iii@...ux.ibm.com, huschle@...ux.ibm.com, rostedt@...dmis.org,
 dietmar.eggemann@....com
Subject: Re: [PATCH 00/17] Paravirt CPUs and push task for less vCPU
 preemption

Hi Shrikanth,

Le 25/11/2025 à 03:39, Shrikanth Hegde a écrit :
> Hi Greg.
> 
> On 11/24/25 10:35 PM, Greg KH wrote:
>> On Wed, Nov 19, 2025 at 06:14:32PM +0530, Shrikanth Hegde wrote:
>>> Detailed problem statement and some of the implementation choices were
>>> discussed earlier[1].
>>>
>>> [1]: https://eur01.safelinks.protection.outlook.com/? 
>>> url=https%3A%2F%2Flore.kernel.org%2Fall%2F20250910174210.1969750-1- 
>>> sshegde%40linux.ibm.com%2F&data=05%7C02%7Cchristophe.leroy%40csgroup.eu%7Cc7e5a5830fcb4c796d4808de2bcbe09d%7C8b87af7d86474dc78df45f69a2011bb5%7C0%7C0%7C638996351808032890%7CUnknown%7CTWFpbGZsb3d8eyJFbXB0eU1hcGkiOnRydWUsIlYiOiIwLjAuMDAwMCIsIlAiOiJXaW4zMiIsIkFOIjoiTWFpbCIsIldUIjoyfQ%3D%3D%7C0%7C%7C%7C&sdata=cV8RTPdV3So1GwQ9uVYgUuGxSfxutSezpaNBq6RYn%2FI%3D&reserved=0
>>>
>>> This is likely the version which would be used for LPC2025 discussion on
>>> this topic. Feel free to provide your suggestion and hoping for a 
>>> solution
>>> that works for different architectures and it's use cases.
>>>
>>> All the existing alternatives such as cpu hotplug, creating isolated
>>> partitions etc break the user affinity. Since number of CPUs to use 
>>> change
>>> depending on the steal time, it is not driven by User. Hence it would be
>>> wrong to break the affinity. This series allows if the task is pinned
>>> only paravirt CPUs, it will continue running there.
>>>
>>> Changes compared v3[1]:
>>
>> There is no "v" for this series :(
>>
> 
> I thought about adding v1.
> 
> I made it as PATCH from RFC PATCH since functionally it should
> be complete now with arch bits. Since it is v1, I remember usually 
> people send out without adding v1. after v1 had tags such as v2.
> 
> I will keep v2 for the next series.
> 

But you are listing changes compared to v3, how can it be a v1 ? 
Shouldn't it be a v4 ? Or in reality a v5 as you already sent a v4 here [1].

[1] 
https://lore.kernel.org/all/20251119062100.1112520-1-sshegde@linux.ibm.com/

Christophe