linux-kernel - Re: [PATCH 1/2] memory: samsung: exynos5422-dmc: Adjust polling interval and uptreshold

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Date:   Fri, 10 Jul 2020 15:19:21 +0200
From:   Krzysztof Kozlowski <krzk@...nel.org>
To:     Marek Szyprowski <m.szyprowski@...sung.com>
Cc:     Lukasz Luba <lukasz.luba@....com>,
        Chanwoo Choi <cw00.choi@...sung.com>,
        linux-kernel@...r.kernel.org, linux-pm@...r.kernel.org,
        linux-arm-kernel@...ts.infradead.org,
        linux-samsung-soc@...r.kernel.org, willy.mh.wolff.ml@...il.com,
        k.konieczny@...sung.com, b.zolnierkie@...sung.com,
        chanwoo@...nel.org, myungjoo.ham@...sung.com,
        kyungmin.park@...sung.com, s.nawrocki@...sung.com, kgene@...nel.org
Subject: Re: [PATCH 1/2] memory: samsung: exynos5422-dmc: Adjust polling
 interval and uptreshold

On Fri, Jul 10, 2020 at 03:13:18PM +0200, Marek Szyprowski wrote:
> Hi Lukasz,
> 
> On 10.07.2020 10:34, 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@...il.com>
> >>> Signed-off-by: Lukasz Luba <lukasz.luba@....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@...sung.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.
> 
> Is there really a need to remove the interrupts property? imho they are 
> correct hw description, it just a matter of the driver to use or not to 
> use them.

That's actually very good point. I would also prefer to leave them.
However I understood that driver chooses mode depending on the property.

In such case, maybe as you said, let's switch to polling mode
unconditionally?

Best regards,
Krzysztof