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Subject: Re: [PATCH 1/2] memory: samsung: exynos5422-dmc: Adjust polling
 interval and uptreshold
To:     Lukasz Luba <lukasz.luba@arm.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
From:   Bartlomiej Zolnierkiewicz <b.zolnierkie@samsung.com>
Message-ID: <ef88644a-a75d-82c0-8b60-eb2810c68f58@samsung.com>
Date:   Fri, 10 Jul 2020 15:49:33 +0200
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        <CGME20200708153448epcas1p438fae2327ac69fcc1a78d9c73cfda501@epcas1p4.samsung.com>
        <20200708153420.29484-2-lukasz.luba@arm.com>
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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?

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)?

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
>>