From: Leonard Crestez <leonard.crestez@nxp.com> To: Chanwoo Choi <cw00.choi@samsung.com>, Matthias Kaehlcke <mka@chromium.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: "Kyungmin Park" <kyungmin.park@samsung.com>, "MyungJoo Ham" <myungjoo.ham@samsung.com>, "Artur Świgoń" <a.swigon@partner.samsung.com>, "Saravana Kannan" <saravanak@google.com>, "Krzysztof Kozlowski" <krzk@kernel.org>, "Alexandre Bailon" <abailon@baylibre.com>, "Georgi Djakov" <georgi.djakov@linaro.org>, "Jacky Bai" <ping.bai@nxp.com>, "Viresh Kumar" <viresh.kumar@linaro.org>, "NXP Linux Team" <linux-imx@nxp.com>, linux-pm@vger.kernel.org, linux-arm-kernel@lists.infradead.org Subject: [PATCH RFC 0/2] PM / devfreq: Add dev_pm_qos support with minimal changes Date: Tue, 19 Nov 2019 18:12:12 +0200 [thread overview] Message-ID: <cover.1574179738.git.leonard.crestez@nxp.com> (raw) 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, this means that calls into dev_pm_qos while holding devfreq->lock are not allowed (lockdep warns about possible deadlocks). Fix this by only adding the qos request and notifiers after devfreq->lock is released inside devfreq_add_device. In theory this means sysfs writes are possible before the min/max requests are initialized so we guard against that explictly. The dev_pm_qos_update_request function would otherwise print a big WARN splat. Alternatively devfreq initialization could be refactored to avoid taking devfreq->lock but that requires several intricate changes: https://patchwork.kernel.org/cover/11242865/ I considered making dev_pm_qos call notifiers outside the lock but that's another complex refactoring and it's difficult to ensure correctness. If two identical qos requests are made in parallel then the second shouldn't return until all notifiers are completely executed for the first and QOS is enforced; otherwise it mostly defeats the purpose of making proactive requests. This series implements the minimal changes in order to implement dev_pm_qos support for devfreq. It only costs a little defensive programming. This series is also marked as [RFC] because it depends on restoring DEV_PM_QOS_MIN/MAX_FREQUENCY inside the pm core: https://patchwork.kernel.org/cover/11250413/ --- Changes since "big version" v10: * Drop accepted cleanups * Work with current locking approach (split cleanups into other series) * Drop acks and deliberately relabel as a new series. It still incorporates most previous discussion but takes a different approach to locking. * Don't print errors if devfreq_dev_release is called on error cleanup from devfreq_add_device, just accept that requests and notifiers might not be registered yet. I wish dev_pm_qos cleanups behaved like standard "kfree" and silently did nothing when there's nothing to be done. Link to v10: https://patchwork.kernel.org/project/linux-arm-kernel/list/?series=196443 Leonard Crestez (2): PM / devfreq: Add PM QoS support PM / devfreq: Use PM QoS for sysfs min/max_freq drivers/devfreq/devfreq.c | 151 ++++++++++++++++++++++++++++++++++---- include/linux/devfreq.h | 14 +++- 2 files changed, 145 insertions(+), 20 deletions(-) -- 2.17.1
WARNING: multiple messages have this Message-ID (diff)
From: Leonard Crestez <leonard.crestez@nxp.com> To: Chanwoo Choi <cw00.choi@samsung.com>, Matthias Kaehlcke <mka@chromium.org>, "Rafael J. Wysocki" <rjw@rjwysocki.net> Cc: "Artur Świgoń" <a.swigon@partner.samsung.com>, "Jacky Bai" <ping.bai@nxp.com>, "Saravana Kannan" <saravanak@google.com>, linux-pm@vger.kernel.org, "Viresh Kumar" <viresh.kumar@linaro.org>, "Krzysztof Kozlowski" <krzk@kernel.org>, "Kyungmin Park" <kyungmin.park@samsung.com>, "MyungJoo Ham" <myungjoo.ham@samsung.com>, "Alexandre Bailon" <abailon@baylibre.com>, "Georgi Djakov" <georgi.djakov@linaro.org>, linux-arm-kernel@lists.infradead.org, "NXP Linux Team" <linux-imx@nxp.com> Subject: [PATCH RFC 0/2] PM / devfreq: Add dev_pm_qos support with minimal changes Date: Tue, 19 Nov 2019 18:12:12 +0200 [thread overview] Message-ID: <cover.1574179738.git.leonard.crestez@nxp.com> (raw) 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, this means that calls into dev_pm_qos while holding devfreq->lock are not allowed (lockdep warns about possible deadlocks). Fix this by only adding the qos request and notifiers after devfreq->lock is released inside devfreq_add_device. In theory this means sysfs writes are possible before the min/max requests are initialized so we guard against that explictly. The dev_pm_qos_update_request function would otherwise print a big WARN splat. Alternatively devfreq initialization could be refactored to avoid taking devfreq->lock but that requires several intricate changes: https://patchwork.kernel.org/cover/11242865/ I considered making dev_pm_qos call notifiers outside the lock but that's another complex refactoring and it's difficult to ensure correctness. If two identical qos requests are made in parallel then the second shouldn't return until all notifiers are completely executed for the first and QOS is enforced; otherwise it mostly defeats the purpose of making proactive requests. This series implements the minimal changes in order to implement dev_pm_qos support for devfreq. It only costs a little defensive programming. This series is also marked as [RFC] because it depends on restoring DEV_PM_QOS_MIN/MAX_FREQUENCY inside the pm core: https://patchwork.kernel.org/cover/11250413/ --- Changes since "big version" v10: * Drop accepted cleanups * Work with current locking approach (split cleanups into other series) * Drop acks and deliberately relabel as a new series. It still incorporates most previous discussion but takes a different approach to locking. * Don't print errors if devfreq_dev_release is called on error cleanup from devfreq_add_device, just accept that requests and notifiers might not be registered yet. I wish dev_pm_qos cleanups behaved like standard "kfree" and silently did nothing when there's nothing to be done. Link to v10: https://patchwork.kernel.org/project/linux-arm-kernel/list/?series=196443 Leonard Crestez (2): PM / devfreq: Add PM QoS support PM / devfreq: Use PM QoS for sysfs min/max_freq drivers/devfreq/devfreq.c | 151 ++++++++++++++++++++++++++++++++++---- include/linux/devfreq.h | 14 +++- 2 files changed, 145 insertions(+), 20 deletions(-) -- 2.17.1 _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel
next reply other threads:[~2019-11-19 16:13 UTC|newest] Thread overview: 18+ messages / expand[flat|nested] mbox.gz Atom feed top 2019-11-19 16:12 Leonard Crestez [this message] 2019-11-19 16:12 ` [PATCH RFC 0/2] PM / devfreq: Add dev_pm_qos support with minimal changes Leonard Crestez 2019-11-19 16:12 ` [PATCH RFC 1/2] PM / devfreq: Add PM QoS support Leonard Crestez 2019-11-19 16:12 ` Leonard Crestez 2019-12-02 1:13 ` Chanwoo Choi 2019-12-02 1:13 ` Chanwoo Choi 2019-11-19 16:12 ` [PATCH RFC 2/2] PM / devfreq: Use PM QoS for sysfs min/max_freq Leonard Crestez 2019-11-19 16:12 ` Leonard Crestez 2019-11-21 23:16 ` Matthias Kaehlcke 2019-11-21 23:16 ` Matthias Kaehlcke 2019-11-25 16:46 ` Leonard Crestez 2019-11-25 16:46 ` Leonard Crestez 2019-12-02 1:18 ` Chanwoo Choi 2019-12-02 1:18 ` Chanwoo Choi 2019-12-04 10:46 ` [PATCH RFC 0/2] PM / devfreq: Add dev_pm_qos support with minimal changes Rafael J. Wysocki 2019-12-04 10:46 ` Rafael J. Wysocki 2019-12-05 0:52 ` Chanwoo Choi 2019-12-05 0:52 ` Chanwoo Choi
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