Re: [PATCH] memory/samsung: reduce unnecessary mutex lock area

[Lukasz Luba]

On 5/12/20 10:05 AM, Krzysztof Kozlowski wrote:
> On Tue, 12 May 2020 at 10:47, Lukasz Luba <lukasz.luba@xxxxxxx> wrote:
> > Hi Krzysztof,
> >
> > I am sorry, I was a bit busy recently.
> >
> > On 5/12/20 7:50 AM, Krzysztof Kozlowski wrote:
> > > On Fri, May 08, 2020 at 06:13:38AM -0700, Bernard Zhao wrote:
> > > > Maybe dmc->df->lock is unnecessary to protect function
> > > > exynos5_dmc_perf_events_check(dmc). If we have to protect,
> > > > dmc->lock is more better and more effective.
> > > > Also, it seems not needed to protect "if (ret) & dev_warn"
> > > > branch.
> > > >
> > > > Signed-off-by: Bernard Zhao <bernard@xxxxxxxx>
> > > > ---
> > > >    drivers/memory/samsung/exynos5422-dmc.c | 6 ++----
> > > >    1 file changed, 2 insertions(+), 4 deletions(-)
> > >
> > > I checked the concurrent accesses and it looks correct.
> > >
> > > Lukasz, any review from your side?
> >
> > The lock from devfreq lock protects from a scenario when
> > concurrent access from devfreq framework uses internal dmc fields 'load'
> > and 'total' (which are set to 'busy_time', 'total_time').
> > The .get_dev_status can be called at any time (even due to thermal
> > devfreq cooling action) and reads above fields.
> > That's why the calculation of the new values inside dmc is protected.
>
> I looked at this path (get_dev_status) and currently in devfreq it
> will be only called from update_devfreq() -> get_target_freq()... at
> least when looking at devfreq core and governors. On the other hand
> you are right that this is public function and this call scenario
> might change. It could be called directly from other paths sooner or
> later.

Indeed, I am currently changing this while I am adding devfreq devices
to the Energy Model.

> > This patch should not be taken IMO. Maybe we can release lock before the
> > if statement, just to speed-up.
>
> Yep.
>
> Bernard, you can send just this part of the patch.

Thank you Bernard and please submit the patch v2.

> Best regards,
> Krzysztof

Thank you Krzysztof for your time spent on this.


Regards,
Lukasz