From: Krzysztof Kozlowski <krzk@xxxxxxxxxx> Date: 2020-05-12 17:05:28 To: Lukasz Luba <lukasz.luba@xxxxxxx> Cc: Bernard Zhao <bernard@xxxxxxxx>,Kukjin Kim <kgene@xxxxxxxxxx>,linux-pm@xxxxxxxxxxxxxxx,"linux-samsung-soc@xxxxxxxxxxxxxxx" <linux-samsung-soc@xxxxxxxxxxxxxxx>,linux-arm-kernel@xxxxxxxxxxxxxxxxxxx,"linux-kernel@xxxxxxxxxxxxxxx" <linux-kernel@xxxxxxxxxxxxxxx>,opensource.kernel@xxxxxxxx Subject: Re: [PATCH] memory/samsung: reduce unnecessary mutex lock area>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. > >> 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. > Sure, I will resubmit a patch in v2. Best regards, Bernard >Best regards, >Krzysztof
