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

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Date: Sat, 24 Feb 2024 08:45:06 +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 11:58 AM, Raghavendra K T wrote:
> 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.
> 

I see that

d) patched + PREEMPT_AUTO=y voluntary preemption CONFIG_PREEMPT, 
PREEMPT_RCU = y

All the results at 80% confidence
		case (d)
HashJoin         0%
Graph500         0%
XSBench          +1.2%
NAS-ft           +2.1%

In general averages are better for all the benchmarks but at 99%
confidence there seem to be no difference.

Overall looks on par or better for case (d)

Thanks and Regards
- Raghu