linux-kernel - Re: [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling

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Date: Fri, 23 Feb 2024 11:58:09 +0530
From: Raghavendra K T <raghavendra.kt@....com>
To: Ankur Arora <ankur.a.arora@...cle.com>,
 Thomas Gleixner <tglx@...utronix.de>
Cc: linux-kernel@...r.kernel.org, peterz@...radead.org,
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Subject: Re: [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling

On 2/23/2024 8:44 AM, Ankur Arora wrote:
> 
> Thomas Gleixner <tglx@...utronix.de> writes:
> 
>> On Wed, Feb 21 2024 at 22:57, Raghavendra K T wrote:
>>> On 2/21/2024 10:45 PM, Thomas Gleixner wrote:
>>>> On Wed, Feb 21 2024 at 17:53, Raghavendra K T wrote:
>>>>> Configuration tested.
>>>>> a) Base kernel (6.7),
>>>>
>>>> Which scheduling model is the baseline using?
>>>>
>>>
>>> baseline is also PREEMPT_DYNAMIC with voluntary preemption
>>>
>>>>> b) patched with PREEMPT_AUTO voluntary preemption.
>>>>> c) patched with PREEMPT_DYNAMIC voluntary preemption.
>>
>> Which RCU variant do you have enabled with a, b, c ?
>>
>> I.e. PREEMPT_RCU=?
> 
> Raghu please confirm this, but if the defaults were chosen
> then we should have:
> 
>>> baseline is also PREEMPT_DYNAMIC with voluntary preemption
> PREEMPT_RCU=y
> 
>>>>> b) patched with PREEMPT_AUTO voluntary preemption.
> 
> If this was built with PREEMPT_VOLUNTARY then, PREEMPT_RCU=n.
> If with CONFIG_PREEMPT, PREEMPT_RCU=y.
> 
> Might be worth rerunning the tests with the other combination
> as well (still with voluntary preemption).
> 
>>>>> c) patched with PREEMPT_DYNAMIC voluntary preemption.
> PREEMPT_RCU=y

Hello Thomas, Ankur,
Yes, Ankur's understanding is right, defaults were chosen all the time so
for
a) base 6.7.0+ + PREEMPT_DYNAMIC with voluntary preemption PREEMPT_RCU=y
b) patched + PREEMPT_AUTO voluntary preemption. PREEMPT_RCU = n
c) patched + PREEMPT_DYNAMIC with voluntary preemption PREEMPT_RCU=y

I will check with other combination (CONFIG_PREEMPT/PREEMPT_RCU) for (b)
and comeback if I see anything interesting.

Thanks and Regards
- Raghu