From mboxrd@z Thu Jan 1 00:00:00 1970 From: Dmitry Osipenko Subject: Re: [PATCH v4 05/16] PM / devfreq: tegra: Don't set EMC clock rate to maximum on probe Date: Tue, 4 Jun 2019 16:05:31 +0300 Message-ID: <71f7b41c-b33f-92fa-e0a5-85fefeb57274@gmail.com> References: <20190501233815.32643-1-digetx@gmail.com> <20190501233815.32643-6-digetx@gmail.com> <20190604110042.GE16519@ulmo> Mime-Version: 1.0 Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 8bit Return-path: In-Reply-To: <20190604110042.GE16519@ulmo> Content-Language: en-US Sender: linux-kernel-owner@vger.kernel.org To: Thierry Reding Cc: Jonathan Hunter , MyungJoo Ham , Kyungmin Park , Chanwoo Choi , Tomeu Vizoso , linux-pm@vger.kernel.org, linux-tegra@vger.kernel.org, linux-kernel@vger.kernel.org List-Id: linux-tegra@vger.kernel.org 04.06.2019 14:00, Thierry Reding пишет: > On Thu, May 02, 2019 at 02:38:04AM +0300, Dmitry Osipenko wrote: >> There is no real benefit from doing so, hence let's drop that rate setting >> for consistency. >> >> Reviewed-by: Chanwoo Choi >> Signed-off-by: Dmitry Osipenko >> --- >> drivers/devfreq/tegra-devfreq.c | 2 -- >> 1 file changed, 2 deletions(-) > > Do you have any numbers to tell how long it would take for the EMC rate > to get incremented? My understanding is that ACTMON basically reacts to > system load, so I could imagine that not setting to the maximum > frequency after this is loaded might make the system slow in the short > term. Only after ACTMON has collected enough data to determine that it > needs to clock the EMC higher would system speed resume normal. > > I guess technically this patch doesn't change anything if the system > already boots at the highest EMC frequency anyway, which I think it does > on many (although not all) devices. > > Anyway, you said you've tested this and are satisfied with the > performance, so it can't be that bad: > > Acked-by: Thierry Reding It takes 12ms for ACTMON to react and then about (couple) hundred microseconds to change memory freq. This is a very short period of time that human being can't notice. AFAIK, in practice there are no devices in the wild that boot up with DRAM clocked at lowest rate. Most devices have a video output and thus require significant memory bandwidth at a boot time already. Secondly, higher memory bandwidth is only really needed for a cases like multimedia, in most generic cases CPU is hitting cache and not utilizing DRAM a lot.