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Mon, 19 Oct 2020 02:46:35 -0700 (PDT) Date: Mon, 19 Oct 2020 15:16:33 +0530 From: Viresh Kumar To: Nicola Mazzucato Subject: Re: [PATCH v2 2/2] [RFC] CPUFreq: Add support for cpu-perf-dependencies Message-ID: <20201019094633.m3yvxurfm2xwsb6a@vireshk-i7> References: <2417d7b5-bc58-fa30-192c-e5991ec22ce0@arm.com> <20201008110241.dcyxdtqqj7slwmnc@vireshk-i7> <20201008150317.GB20268@arm.com> <56846759-e3a6-9471-827d-27af0c3d410d@arm.com> <20201009053921.pkq4pcyrv4r7ylzu@vireshk-i7> <20201012154915.GD16519@bogus> <20201012165219.GA3573@arm.com> <17819d4d-9e7e-9a38-4227-d0d10a0749f1@arm.com> <20201014042531.r7iykzygkvmpsqck@vireshk-i7> <503af305-77a4-964a-ed17-8df8b4e3a546@arm.com> MIME-Version: 1.0 Content-Disposition: inline In-Reply-To: <503af305-77a4-964a-ed17-8df8b4e3a546@arm.com> User-Agent: NeoMutt/20180716-391-311a52 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20201019_054638_242480_3498C9CF X-CRM114-Status: GOOD ( 36.25 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: devicetree@vger.kernel.org, linux-pm@vger.kernel.org, vireshk@kernel.org, daniel.lezcano@linaro.org, rjw@rjwysocki.net, linux-kernel@vger.kernel.org, robh+dt@kernel.org, linux-arm-kernel@lists.infradead.org, Sudeep Holla , chris.redpath@arm.com, Ionela Voinescu , morten.rasmussen@arm.com, Lukasz Luba Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+linux-arm-kernel=archiver.kernel.org@lists.infradead.org On 19-10-20, 09:50, Nicola Mazzucato wrote: > Hi Viresh, > > thank you for your suggestion on using 'opp-shared'. > I think it could work for most of the cases we explained earlier. > > Summarising, there are two parts of this entire proposal: > 1) where/how to get the information: now we are focusing on taking advantage of > 'opp-shared' within an empty opp table > 2) and how/where this information will be consumed > > Further details below: > > 1) a CPUFreq driver that takes the OPPs from firmware, can call > dev_pm_opp_of_get_sharing_cpus like you suggested. When doing so, a provided > cpumaksk will be populated with the corresponding cpus that share the same > (empty) table opp in DT. > All good so far. Great. > The current opp core is not expecting an empty table and therefore some errors > are thrown when this happens. > Since we are now allowing this corner-case, I am presenting below where I think > some minor corrections may be needed: > > --- a/drivers/opp/of.c > +++ b/drivers/opp/of.c > @@ static void _opp_table_alloc_required_tables(struct opp_table *opp_table, > struct device_node *required_np, *np; > int count, i; > > /* Traversing the first OPP node is all we need */ > np = of_get_next_available_child(opp_np, NULL); > if (!np) { > - dev_err(dev, "Empty OPP table\n"); > + dev_warn(dev, "Empty OPP table\n"); > + > + /* > + * With empty table we remove shared_opp. This is to leave the > + * responsibility to decide which opp are shared to the opp users > + */ > + opp_table->shared_opp = OPP_TABLE_ACCESS_EXCLUSIVE; > + > return; > } > > @@ int dev_pm_opp_of_find_icc_paths(struct device *dev, > int ret, i, count, num_paths; > struct icc_path **paths; > > ret = _bandwidth_supported(dev, opp_table); > - if (ret <= 0) > + if (ret == -EINVAL) > + return 0; /* Empty OPP table is a valid corner-case, let's not > fail */ > + else if (ret <= 0) > return ret; > > The above are not 'strictly' necessary to achieve the intended goal, but they > make clearer that an empty table is now allowed and not an error anymore. > What it is your point of view on this? Why is this stuff getting called in your case ? We shouldn't be trying to create an OPP table here and it should still be an error in the code if we are asked to parse an empty OPP table. > In addition, I think it would also be appropriate to update the documentation > (Documentation/devicetree/bindings/opp/opp.txt) to reflect this new case > (required properties etc). > Any different thoughts? Yes, this needs a small update in the required-opps section. > 2) Once the driver gets the 'performance dependencies' by > dev_pm_opp_of_get_sharing_cpus(), this information will have to be shared with > EAS, thermal, etc.. The natural way to do so would be to add a new cpumask like > I proposed in this RFC. > I see this as an improvement for the whole subsystem and a scalable choice since > we can unambiguously provide the correct information to whoever needs it, given > that we don't enforce "hw dependencies" for related_cpus. > The changes would be trivial (it's in the original RFC). > On the other hand, we can't unload this h/w detail into related_cpus IMO as we > are dealing with per-cpu systems in this context. > Hope it makes sense? I will have another look at this stuff, honestly I haven't looked at this in detail yet. But I do understand that we can't really use related-cpu here without changing its earlier meaning. -- viresh _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel