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Subject: Re: [PATCH 1/2] memory: samsung: exynos5422-dmc: Adjust polling
 interval and uptreshold
To:     Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Cc:     Krzysztof Kozlowski <krzk@kernel.org>,
        Chanwoo Choi <cw00.choi@samsung.com>,
        linux-kernel@vger.kernel.org, linux-pm@vger.kernel.org,
        linux-arm-kernel@lists.infradead.org,
        linux-samsung-soc@vger.kernel.org, willy.mh.wolff.ml@gmail.com,
        k.konieczny@samsung.com, chanwoo@kernel.org,
        myungjoo.ham@samsung.com, kyungmin.park@samsung.com,
        s.nawrocki@samsung.com, kgene@kernel.org
References: <20200708153420.29484-1-lukasz.luba@arm.com>
 <CGME20200708153448epcas1p438fae2327ac69fcc1a78d9c73cfda501@epcas1p4.samsung.com>
 <20200708153420.29484-2-lukasz.luba@arm.com>
 <fa3f651a-3c2b-188b-e2dc-4fd05ce4a1b7@samsung.com>
 <a676fc18-6f1f-8502-e8d5-5ad1ccf0eec6@arm.com> <20200710124503.GB22897@pi3>
 <0bfb4332-9a2e-9ff9-1a86-d9875a8f34bb@arm.com>
 <ef88644a-a75d-82c0-8b60-eb2810c68f58@samsung.com>
From:   Lukasz Luba <lukasz.luba@arm.com>
Message-ID: <b0ecbdd9-f445-b2f7-755a-cbc10cb1e56c@arm.com>
Date:   Fri, 10 Jul 2020 15:00:37 +0100
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On 7/10/20 2:49 PM, Bartlomiej Zolnierkiewicz wrote:
> 
> On 7/10/20 2:56 PM, Lukasz Luba wrote:
>>
>>
>> On 7/10/20 1:45 PM, Krzysztof Kozlowski wrote:
>>> On Fri, Jul 10, 2020 at 09:34:45AM +0100, Lukasz Luba wrote:
>>>> Hi Chanwoo,
>>>>
>>>> On 7/9/20 5:08 AM, Chanwoo Choi wrote:
>>>>> Hi Lukasz,
>>>>>
>>>>> On 7/9/20 12:34 AM, Lukasz Luba wrote:
>>>>>> In order to react faster and make better decisions under some workloads,
>>>>>> benchmarking the memory subsystem behavior, adjust the polling interval
>>>>>> and upthreshold value used by the simple_ondemand governor.
>>>>>>
>>>>>> Reported-by: Willy Wolff <willy.mh.wolff.ml@gmail.com>
>>>>>> Signed-off-by: Lukasz Luba <lukasz.luba@arm.com>
>>>>>> ---
>>>>>>     drivers/memory/samsung/exynos5422-dmc.c | 4 ++--
>>>>>>     1 file changed, 2 insertions(+), 2 deletions(-)
>>>>>>
>>>>>> diff --git a/drivers/memory/samsung/exynos5422-dmc.c b/drivers/memory/samsung/exynos5422-dmc.c
>>>>>> index 93e9c2429c0d..e03ee35f0ab5 100644
>>>>>> --- a/drivers/memory/samsung/exynos5422-dmc.c
>>>>>> +++ b/drivers/memory/samsung/exynos5422-dmc.c
>>>>>> @@ -1466,10 +1466,10 @@ static int exynos5_dmc_probe(struct platform_device *pdev)
>>>>>>              * Setup default thresholds for the devfreq governor.
>>>>>>              * The values are chosen based on experiments.
>>>>>>              */
>>>>>> -        dmc->gov_data.upthreshold = 30;
>>>>>> +        dmc->gov_data.upthreshold = 10;
>>>>>>             dmc->gov_data.downdifferential = 5;
>>>>>> -        exynos5_dmc_df_profile.polling_ms = 500;
>>>>>> +        exynos5_dmc_df_profile.polling_ms = 100;
>>>>>>         }
>>>>>>
>>>>>
>>>>> Reviewed-by: Chanwoo Choi <cw00.choi@samsung.com>
>>>>>
>>>>
>>>> Thank you for the review. Do you think this patch could go through
>>>> your tree together with your patches?
>>>>
>>>> I don't know Krzysztof's opinion about the patch 2/2, but
>>>> I would expect, assuming the patch itself is correct, he would
>>>> like to take it into his next/dt branch.
>>>
>>> In the cover letter you mentioned that this is a follow up for the
>>> Chanwoo's patchset. But are these patches really depending on it? Can
>>> they be picked up independently?
>>
>>
>> They are not heavily dependent on Chanwoo's patches.
>> Yes, they can be picked up independently.
> 
> Hmmm, are you sure?

In a sense: in two phases (first the Chanwoo's changes land into
devfreq, then when Krzysztof prepares his topic branches for
arm soc, I assumed Chanwoo's patches are mainline and will be there
already).

> 
> Sure, they will apply fine but without Chanwoo's patches won't they
> cause the dmc driver to use using polling mode with deferred timer
> (unintended/bad behavior) instead of IRQs (current behavior) or
> polling mode with delayed timer (future behavior)?

I was assuming that it will take longer, when Krzysztof is going to pick
patch 2/2, definitely after a while (and it could be also the case for
patch 1/1 if Krzysztof was going to take it).

I think there is no rush and it can go in two phases.

Good point Bartek for clarifying this. I wasn't clear in the messages.
Thank you for keeping eye on this.

Regards,
Lukasz


> 
> Best regards,
> --
> Bartlomiej Zolnierkiewicz
> Samsung R&D Institute Poland
> Samsung Electronics
> 
>> I just wanted to mention that the patch 1/2 was produced on the
>> code base which had already applied Chanwoo's patch for DMC.
>> If you like to take both 1/2 and 2/2 into your tree, it's good.
>>
>> Thank you for having a look on this.
>>
>> Regards,
>> Lukasz
>>
>>
>>>
>>> The DTS patch must go through arm soc, so I will take it. If it really
>>> depends on driver changes, then it has to wait for next release.
>>>
>>> Best regards,
>>> Krzysztof
>>>
>