From: Leonard Crestez <firstname.lastname@example.org> To: Matthias Kaehlcke <email@example.com> Cc: "MyungJoo Ham" <firstname.lastname@example.org>, "Rafael J. Wysocki" <email@example.com>, "Chanwoo Choi" <firstname.lastname@example.org>, "Kyungmin Park" <email@example.com>, "Artur Świgoń" <firstname.lastname@example.org>, "Saravana Kannan" <email@example.com>, "Krzysztof Kozlowski" <firstname.lastname@example.org>, "Alexandre Bailon" <email@example.com>, "Georgi Djakov" <firstname.lastname@example.org>, "Abel Vesa" <email@example.com>, "Jacky Bai" <firstname.lastname@example.org>, "Viresh Kumar" <email@example.com>, dl-linux-imx <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org>, "email@example.com" <firstname.lastname@example.org> Subject: Re: [PATCH v9 0/8] PM / devfreq: Add dev_pm_qos support Date: Thu, 24 Oct 2019 16:21:12 +0000 Message-ID: <VI1PR04MB70236FB8DCC401EEAF97A424EE6A0@VI1PR04MB7023.eurprd04.prod.outlook.com> (raw) In-Reply-To: <20191023163443.GL20212@google.com> On 23.10.2019 19:34, Matthias Kaehlcke wrote: > On Wed, Oct 23, 2019 at 02:06:40PM +0000, Leonard Crestez wrote: >> On 2019-10-02 10:25 PM, Leonard Crestez wrote: >>> Add dev_pm_qos notifiers to devfreq core in order to support frequency >>> limits via dev_pm_qos_add_request. >>> >>> Unlike the rest of devfreq the dev_pm_qos frequency is measured in Khz, >>> this is consistent with current dev_pm_qos usage for cpufreq and >>> allows frequencies above 2Ghz (pm_qos expresses limits as s32). >>> >>> Like with cpufreq the handling of min_freq/max_freq is moved to the >>> dev_pm_qos mechanism. Constraints from userspace are no longer clamped on >>> store, instead all values can be written and we only check against OPPs in a >>> new devfreq_get_freq_range function. This is consistent with the design of >>> dev_pm_qos. >>> >>> Notifiers from pm_qos are executed under a single global dev_pm_qos_mtx and >>> need to take devfreq->lock. Notifier registration takes the same dev_pm_qos_mtx >>> so in order to prevent lockdep warnings it must be done outside devfreq->lock. >>> Current devfreq_add_device does all initialization under devfreq->lock and that >>> needs to be relaxed. >>> >>> Some of first patches in the series are bugfixes and cleanups, they could be >>> applied separately. >> >> Hello, >> >> This series was posted a few ago and all patches have been >> reviewed/tested-by multiple people. Possible minor hangups: >> >> 1) Matthias found it confusing that min/max_freq in sysfs changes >> on-the-fly. This is not a behavior change and I believe a decent >> workaround would be to implement separate user_min/max_freq files from >> which userspace will always read back the contraints it has written. > > As you said, it isn't a behavioral change, so it shouldn't be an issue > for this series. > > Regarding the workaround I think it would be clearer to have new > xyx_min/max_freq files for the aggregate values. min/max_freq are the > interface userspace uses to specify the limits, it would be strange to > use different files to read them out. > > In any case the aggregate values seem to be of little practical value, > except perhaps for monitoring, since they could be stale right after > userspace read them out. We could start with not providing them, and add > them if it turns out that they are actually needed. But the min/max_freq files right now already are already aggregates and sysfs is considered ABI. I wouldn't be surprised if somebody has an userspace daemon which uses them. My proposal is to add user_min/max_freq as a new finer-grained interface that you can both read and write to, no confusion here. Writes to min/max_freq would still be supported but only for compatibility with older releases. >> 2) There was an objection to removing devm from two allocs in PATCH 4. I >> believe current solution is acceptable but a possible alternative would >> be to split device_register into device_initialize and device_add: this >> should allow devm sooner. >> Link: https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.kernel.org%2Fpatch%2F11158385%2F%2322902151&data=02%7C01%7Cleonard.crestez%40nxp.com%7Cb89f3efc3c934030fb6108d757d6ecb2%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637074452911403311&sdata=DeOUpVjT1yZ2EWs50CFL98OoTjVMCpQDCM3qjCtKuW0%3D&reserved=0 >> >> Let me know if you think I should implement the options above and resend. >> >> The bigger problem is that DEV_PM_QOS_MIN/MAX_FREQUENCY was removed from >> pm core because only user (cpufreq) was refactored to use a new >> interface on top of cpufreq_policy. Links to discussion: >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Fpatchwork.kernel.org%2Fcover%2F11193021%2F&data=02%7C01%7Cleonard.crestez%40nxp.com%7Cb89f3efc3c934030fb6108d757d6ecb2%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637074452911408301&sdata=DxfUtaGch6MilSy5fX8AHN3%2BDIp8MrbQrHH%2B6VdRb%2FI%3D&reserved=0 >> >> https://eur01.safelinks.protection.outlook.com/?url=https%3A%2F%2Flore.kernel.org%2Flinux-pm%2FVI1PR04MB7023DF47D046AEADB4E051EBEE680%40VI1PR04MB7023.eurprd04.prod.outlook.com%2FT%2F%23u&data=02%7C01%7Cleonard.crestez%40nxp.com%7Cb89f3efc3c934030fb6108d757d6ecb2%7C686ea1d3bc2b4c6fa92cd99c5c301635%7C0%7C0%7C637074452911408301&sdata=sYQZUbzEk2DsWGQ5eQnu2m2%2Bsp%2BYBO16Abyjwf7Z1sQ%3D&reserved=0 >> >> I believe there is still significant value in supporting min/max >> frequency requests on a per-target-device basis. This makes much more >> sense for devfreq that for cpufreq because the whole point of devfreq is >> scaling arbitrary independent devices. > > Agreed. > > It seems Rafael would be ok with reverting the patch that removes > DEV_PM_QOS_MIN/MAX_FREQUENCY, IIUC he just doesn't want to keep it around > at this time because with the rest of his series there remain no in-tree > users.
prev parent reply index Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-10-02 19:25 Leonard Crestez 2019-10-02 19:25 ` [PATCH v9 1/8] PM / devfreq: Don't fail devfreq_dev_release if not in list Leonard Crestez 2019-10-02 19:25 ` [PATCH v9 2/8] PM / devfreq: Fix devfreq_notifier_call returning errno Leonard Crestez 2019-10-02 21:24 ` Matthias Kaehlcke 2019-10-02 23:47 ` Leonard Crestez 2019-10-31 2:29 ` Chanwoo Choi 2019-10-02 19:25 ` [PATCH v9 3/8] PM / devfreq: Set scaling_max_freq to max on OPP notifier error Leonard Crestez 2019-10-02 21:33 ` Matthias Kaehlcke 2019-10-31 2:21 ` Chanwoo Choi 2019-10-02 19:25 ` [PATCH v9 4/8] PM / devfreq: Move more initialization before registration Leonard Crestez 2019-10-31 3:15 ` Chanwoo Choi 2019-10-31 13:31 ` Leonard Crestez 2019-11-01 8:31 ` Chanwoo Choi 2019-11-01 14:36 ` Leonard Crestez 2019-10-02 19:25 ` [PATCH v9 5/8] PM / devfreq: Don't take lock in devfreq_add_device Leonard Crestez 2019-10-02 19:25 ` [PATCH v9 6/8] PM / devfreq: Introduce get_freq_range helper Leonard Crestez 2019-10-03 18:19 ` Matthias Kaehlcke 2019-10-03 19:16 ` Leonard Crestez 2019-10-03 19:36 ` Matthias Kaehlcke 2019-10-11 18:29 ` Matthias Kaehlcke 2019-10-31 2:44 ` Chanwoo Choi 2019-10-31 2:42 ` Chanwoo Choi 2019-10-31 13:12 ` Leonard Crestez 2019-10-02 19:25 ` [PATCH v9 7/8] PM / devfreq: Add PM QoS support Leonard Crestez 2019-10-02 22:22 ` Matthias Kaehlcke 2019-10-04 17:04 ` Matthias Kaehlcke 2019-10-31 3:01 ` Chanwoo Choi 2019-10-31 13:21 ` Leonard Crestez 2019-10-02 19:25 ` [PATCH v9 8/8] PM / devfreq: Use PM QoS for sysfs min/max_freq Leonard Crestez 2019-10-04 17:05 ` Matthias Kaehlcke 2019-10-31 3:10 ` Chanwoo Choi 2019-10-23 14:06 ` [PATCH v9 0/8] PM / devfreq: Add dev_pm_qos support Leonard Crestez 2019-10-23 16:34 ` Matthias Kaehlcke 2019-10-24 16:21 ` Leonard Crestez [this message]
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