linux-kernel - Re: [PATCH 1/3] soc: qcom: rpmh: Update dirty flag only when data changes

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Message-ID: <4e54da6a-3418-7f06-818c-7d87443b5253@codeaurora.org>
Date:   Wed, 12 Feb 2020 17:11:32 +0530
From:   Maulik Shah <mkshah@...eaurora.org>
To:     Evan Green <evgreen@...omium.org>
Cc:     Bjorn Andersson <bjorn.andersson@...aro.org>,
        Andy Gross <agross@...nel.org>,
        linux-arm-msm <linux-arm-msm@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>,
        Stephen Boyd <swboyd@...omium.org>,
        Doug Anderson <dianders@...omium.org>,
        Rajendra Nayak <rnayak@...eaurora.org>,
        Lina Iyer <ilina@...eaurora.org>, lsrao@...eaurora.org
Subject: Re: [PATCH 1/3] soc: qcom: rpmh: Update dirty flag only when data
 changes


On 2/5/2020 11:37 PM, Evan Green wrote:
> On Tue, Feb 4, 2020 at 8:14 PM Maulik Shah <mkshah@...eaurora.org> wrote:
>>
>> On 2/5/2020 6:05 AM, Evan Green wrote:
>>> On Mon, Feb 3, 2020 at 10:14 PM Maulik Shah <mkshah@...eaurora.org> wrote:
>>>> Currently rpmh ctrlr dirty flag is set for all cases regardless
>>>> of data is really changed or not.
>>>>
>>>> Add changes to update it when data is updated to new values.
>>>>
>>>> Signed-off-by: Maulik Shah <mkshah@...eaurora.org>
>>>> ---
>>>>    drivers/soc/qcom/rpmh.c | 15 +++++++++++----
>>>>    1 file changed, 11 insertions(+), 4 deletions(-)
>>>>
>>>> diff --git a/drivers/soc/qcom/rpmh.c b/drivers/soc/qcom/rpmh.c
>>>> index 035091f..c3d6f00 100644
>>>> --- a/drivers/soc/qcom/rpmh.c
>>>> +++ b/drivers/soc/qcom/rpmh.c
>>>> @@ -139,20 +139,27 @@ static struct cache_req *cache_rpm_request(struct rpmh_ctrlr *ctrlr,
>>>>    existing:
>>>>           switch (state) {
>>>>           case RPMH_ACTIVE_ONLY_STATE:
>>>> -               if (req->sleep_val != UINT_MAX)
>>>> +               if (req->sleep_val != UINT_MAX) {
>>>>                           req->wake_val = cmd->data;
>>>> +                       ctrlr->dirty = true;
>>>> +               }
>>> Don't you need to set dirty = true for ACTIVE_ONLY state always? The
>>> conditional is just saying "if nobody set a sleep vote, then maintain
>>> this vote when we wake back up".
>> The ACTIVE_ONLY vote is cached as wake_val to be apply when wakeup happens.
>>
>> In case value didn't change,wake_val is still same as older value and
>> there is no need to mark the entire cache as dirty.
>>
> Ah, I see it now. We don't actually cache active_only votes anywhere,
> since they're one time requests. The sleep/wake votes seem to be the
> only thing that gets cached.
>
> I was thinking it might be safer to also set dirty = true just after
> list_add_tail, since in the non-existing case this is a new batch that
> RPMh has never seen before and should always be written. But I suppose
> your checks here should cover that case, since sleep_val and wake_val
> are initialized to UINT_MAX. If you think the code might evolve, it
> might still be nice to add it.
current change seems good.
>
> While I'm looking at that, why do we have this needless INIT_LIST_HEAD?
>          INIT_LIST_HEAD(&req->list);
>          list_add_tail(&req->list, &ctrlr->cache);
>
> -Evan

Thanks for pointing this, i will remove this unnecessary INIT in next 
revision.

>
>> --
>> QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation

-- 
QUALCOMM INDIA, on behalf of Qualcomm Innovation Center, Inc. is a member of Code Aurora Forum, hosted by The Linux Foundation