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Date: Tue, 12 May 2020 10:23:03 +0100 From: Lukasz Luba <lukasz.luba@....com> To: Krzysztof Kozlowski <krzk@...nel.org> Cc: Bernard Zhao <bernard@...o.com>, Kukjin Kim <kgene@...nel.org>, linux-pm@...r.kernel.org, "linux-samsung-soc@...r.kernel.org" <linux-samsung-soc@...r.kernel.org>, linux-arm-kernel@...ts.infradead.org, "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>, opensource.kernel@...o.com Subject: Re: [PATCH] memory/samsung: reduce unnecessary mutex lock area On 5/12/20 10:05 AM, Krzysztof Kozlowski wrote: > On Tue, 12 May 2020 at 10:47, Lukasz Luba <lukasz.luba@....com> 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@...o.com> >>>> --- >>>> 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
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