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

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Date:   Mon, 4 Feb 2019 15:52:39 +0000
From:   Sudeep Holla <sudeep.holla@....com>
To:     Greg Kroah-Hartman <gregkh@...uxfoundation.org>
Cc:     "Rafael J. Wysocki" <rjw@...ysocki.net>, 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>,
        Sudeep Holla <sudeep.holla@....com>,
        Joshua Frkuska <joshua_frkuska@...tor.com>
Subject: Re: [RFC PATCH] drivers core: cpu: add hotplug callback to update
 cpu_dev state to resumed

On Mon, Feb 04, 2019 at 04:44:21PM +0100, Greg Kroah-Hartman wrote:
> On Mon, Feb 04, 2019 at 03:37:20PM +0000, 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 ?
>
> Personally, I ignore RFC patches unless I'm accidentally interested in
> them, as it shows that the author doesn't feel good enough to propose
> them as a real solution :)
>

I understand. Since Rafael did suggest alternate approach, just thought
of pinging him to check if I understood his idea.

> But that's just me...
>

:)

Regards,
Sudeep