Re: [PATCH v13 0/4] PM / Domains: Support hierarchical CPU arrangement (PSCI/ARM)

From: Ulf Hansson
Date: Tue Apr 09 2019 - 07:57:42 EST

On Wed, 27 Mar 2019 at 15:35, Ulf Hansson <ulf.hansson@xxxxxxxxxx> wrote:
> Changes in v13:
> - Use WRITE|READ_ONCE when reading/writing the "next_hrtimer" variable in the
> struct cpuidle_device. Also reset the same variable after resumed from idle to
> avoid it from containing a stale value.
> - Added acks from Daniel Lezcano.
> - The entire v13 series, including the PSCI/ARM changes are available in a
> git branch [3].

Rafael, I have address the received comments on this version $subject
series, is there anything that is holding you back from queuing it?

If you like I can send a pull-request, to simplify for you.

Moreover, there is another series which I have pinged you about
earlier, which I would appreciate to queue via your tree. It's acked
by PSCI maintainers and is ready to go. "[PATCH v2 0/5] drivers:
firmware: psci: Some cleanup and refactoring".

Kind regards

> Changes in v12:
> - Drop the patches for restructuring tick_nohz_get_sleep_length(). Instead
> replace them all with a new timer/cpuidle patch, according to suggestions by
> Rafael.
> - The entire v12 series, including the PSCI/ARM changes are available in a
> git branch [2].
> Changes in v11:
> - This version contains only the infrastructure changes that is needed for
> deployment. The PSCI/ARM changes have also been updated and tested, but I will
> post them separately. Still, to provide completeness, I have published a branch
> containing everything to a git tree [1], feel free to have a look and test.
> - The v10 series contained a patch, "timer: Export next wakeup time of a CPU",
> which has been replaced by a couple of new patches, whom reworks the existing
> tick_nohz_get_sleep_length() function, to provide the next timer expiration
> instead of the duration.
> - More changelogs are available per patch.
> Changes in v10:
> - Quite significant changes have been to the PSCI driver deployment. According
> to an agreement with Lorenzo, the hierarchical CPU layout for PSCI should be
> orthogonal to whether the PSCI FW supports OSI or not. This has been taken
> care of in this version.
> - Drop the generic attach/detach helpers of CPUs to genpd, instead make that
> related code internal to PSCI, for now.
> - Fix "BUG: sleeping for invalid context" for hotplug, as reported by Raju.
> - Addressed various comments from version 8 and 9.
> - Clarified changelogs and re-wrote the cover-letter to better explain the
> motivations behind these changes.
> Background:
> For ARM64/ARM based platforms CPUs are often arranged in a hierarchical manner.
> From a CPU idle state perspective, this means some states may be shared among a
> group of CPUs (aka CPU cluster).
> To deal with idle management of a group of CPUs, sometimes the kernel needs to
> be involved to manage the last-man standing algorithm, simply because it can't
> rely solely on power management FWs to deal with this. Depending on the
> platform, of course.
> There are a couple of typical scenarios for when the kernel needs to be in
> control, dealing with synchronization of when the last CPU in a cluster is about
> to enter a deep idle state.
> 1)
> The kernel needs to carry out so called last-man activities before the
> CPU cluster can enter a deep idle state. This may for example involve to
> configure external logics for wakeups, as the GIC may no longer be functional
> once a deep cluster idle state have been entered. Likewise, these operations
> may need to be restored, when the first CPU wakes up.
> 2)
> Other more generic I/O devices, such as an MMC controller for example, may be a
> part of the same power domain as the CPU cluster, due to a shared power-rail.
> For these scenarios, when the MMC controller is in use dealing with an MMC
> request, a deeper idle state of the CPU cluster may needs to be temporarily
> disabled. This is needed to retain the MMC controller in a functional state,
> else it may loose its register-context in the middle of serving a request.
> In this series, we are extending the generic PM domain (aka genpd) to be used
> for also CPU devices. Hence the goal is to re-use much of its current code to
> help us manage the last-man standing synchronization. Moreover, as we already
> use genpd to model power domains for generic I/O devices, both 1) and 2) can be
> address with its help.
> Moreover, to address these problems for ARM64 DT based platforms, we are
> deploying support for genpd and runtime PM to the PSCI FW driver - and finally
> we make some updates to two ARM64 DTBs, as to deploy the new PSCI CPU topology
> layout.
> The series has been tested on a Qcom 410c dragonboard and on a Hisilicon Hikey
> board. The first one uses PSCI OS-initiated mode, while the second uses the PSCI
> Platform-Coordinated mode.
> Kind regards
> Ulf Hansson
> [1]
> next_v11
> [2]
> next_v12
> [2]
> next_v13
> Ulf Hansson (4):
> PM / Domains: Add a generic data pointer to the genpd_power_state
> struct
> PM / Domains: Add support for CPU devices to genpd
> cpuidle: Export the next timer/tick expiration for a CPU
> PM / Domains: Add genpd governor for CPUs
> drivers/base/power/domain.c | 77 ++++++++++++++++++++++++++--
> drivers/base/power/domain_governor.c | 65 ++++++++++++++++++++++-
> drivers/cpuidle/cpuidle.c | 19 ++++++-
> include/linux/cpuidle.h | 1 +
> include/linux/pm_domain.h | 20 +++++++-
> include/linux/tick.h | 7 ++-
> kernel/time/tick-sched.c | 12 +++++
> 7 files changed, 193 insertions(+), 8 deletions(-)
> --
> 2.17.1