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

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Message-ID: <87h6ht94xl.fsf@oracle.com>
Date: Tue, 27 Feb 2024 09:45:42 -0800
From: Ankur Arora <ankur.a.arora@...cle.com>
To: Raghavendra K T <raghavendra.kt@....com>
Cc: Ankur Arora <ankur.a.arora@...cle.com>,
        Thomas Gleixner
 <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
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Subject: Re: [PATCH 00/30] PREEMPT_AUTO: support lazy rescheduling


Raghavendra K T <raghavendra.kt@....com> writes:

> 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 for running all of these Raghu. The numbers look pretty good
(better than I expected honestly).

--
ankur