linux-kernel - Re: [RFC PATCH] drivers core: cpu: add hotplug callback to update cpu

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Message-ID: <2477683.mi0XWuPk1d@aspire.rjw.lan>
Date:   Wed, 06 Feb 2019 11:31:04 +0100
From:   "Rafael J. Wysocki" <rjw@...ysocki.net>
To:     Sudeep Holla <sudeep.holla@....com>
Cc:     linux-pm@...r.kernel.org, linux-kernel@...r.kernel.org,
        Jisheng Zhang <jszhang@...vell.com>,
        Steve Longerbeam <steve_longerbeam@...tor.com>,
        Eugeniu Rosca <roscaeugeniu@...il.com>,
        Joshua Frkuska <joshua_frkuska@...tor.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Subject: Re: [RFC PATCH] drivers core: cpu: add hotplug callback to update cpu_dev state to resumed

On Monday, February 4, 2019 4:37:20 PM CET Sudeep Holla wrote:
> On Thu, Jan 31, 2019 at 04:05:59PM +0000, Sudeep Holla wrote:
> > On Thu, Jan 31, 2019 at 12:48:49AM +0100, Rafael J. Wysocki wrote:
> > > On Friday, January 25, 2019 4:09:06 PM CET Sudeep Holla wrote:
> > > > The sysfs for the cpu caches are managed by adding devices with cpu
> > > > as the parent in cpu_device_create() when secondary cpu is brought
> > > > onlin. Generally when the secondary CPUs are hotplugged back is as part
> > > > of resume from suspend-to-ram, we call cpu_device_create() from the cpu
> > > > hotplug state machine while the cpu device associated with that CPU is
> > > > not yet ready to be resumed as the device_resume() call happens bit later.
> > > > It's not really needed to set the flag is_prepared for cpu devices are
> > > > they are mostly pseudo device and hotplug framework deals with state
> > > > machine and not managed through the cpu device.
> > > >
> > > > This often results in annoying warning when resuming:
> > > > Enabling non-boot CPUs ...
> > > > CPU1: Booted secondary processor
> > > >  cache: parent cpu1 should not be sleeping
> > > > CPU1 is up
> > > > CPU2: Booted secondary processor
> > > >  cache: parent cpu2 should not be sleeping
> > > > CPU2 is up
> > > > .... and so on.
> > > >
> > > > Just fix the warning by updating the device state quite early.
> > > >
> > > > Cc: "Rafael J. Wysocki" <rjw@...ysocki.net>
> > > > Reported-by: Jisheng Zhang <jszhang@...vell.com>
> > > > Reported-by: Steve Longerbeam <slongerbeam@...il.com>
> > > > Reported-by: Eugeniu Rosca <erosca@...adit-jv.com>
> > > > Signed-off-by: Sudeep Holla <sudeep.holla@....com>
> > > > ---
> > > >  drivers/base/cpu.c         | 20 +++++++++++++++++++-
> > > >  include/linux/cpuhotplug.h |  1 +
> > > >  2 files changed, 20 insertions(+), 1 deletion(-)
> > > >
> > > > Hi Rafael,
> > > >
> > > > This is getting reported for quite some time. Let me know if you have
> > > > better solution to fix this harmless yet annoying warnings during system
> > > > resume.
> > >
> > > I'd rather have a flag in struct dev_pm_info that will cause the message to
> > > be suppressed if set.
> > >
> > > It could be used for other purposes too then in princple (like skipping the
> > > creation of empty "power" attr groups in sysfs for devices that don't
> > > need them etc.).
> > >
> > Thanks for the suggestion. I did quick hack and came up with something
> > below. I wanted to run through you once before I materialise it into
> > a formal patch to check if I understood your suggestion correctly.
> > We can move no_pm_required outside dev_pm_info struct and rename with
> > any better names.
> >
> 
> Sorry for the nag, since the title has RFC, thought there are chances of
> this getting lost. Let me know if the below idea aligns with your suggestion ?

RFC would be fine, but Patchwork doesn't pick up patches posted as replies
in the middle of a thread. :-)

Yes, this is basically what I suggested, please post.

Cheers,
Rafael