linux-kernel - Re: CONFIG_ANDROID (was: rcu_sched detected expedited stalls in amdgpu after suspend)

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Message-ID: <20220706204202.GJ1790663@paulmck-ThinkPad-P17-Gen-1>
Date:   Wed, 6 Jul 2022 13:42:02 -0700
From:   "Paul E. McKenney" <paulmck@...nel.org>
To:     Uladzislau Rezki <urezki@...il.com>
Cc:     Christian König <christian.koenig@....com>,
        "Alex Xu (Hello71)" <alex_y_xu@...oo.ca>,
        wireguard@...ts.zx2c4.com, "Jason A. Donenfeld" <Jason@...c4.com>,
        Joel Fernandes <joel@...lfernandes.org>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Xinhui.Pan@....com, linux-kernel@...r.kernel.org,
        amd-gfx@...ts.freedesktop.org,
        Suren Baghdasaryan <surenb@...gle.com>, rcu@...r.kernel.org,
        Hridya Valsaraju <hridya@...gle.com>,
        Arve Hjønnevåg <arve@...roid.com>,
        Theodore Ts'o <tytso@....edu>, alexander.deucher@....com,
        Todd Kjos <tkjos@...roid.com>, uladzislau.rezki@...y.com,
        Martijn Coenen <maco@...roid.com>,
        Christian Brauner <christian@...uner.io>
Subject: Re: CONFIG_ANDROID (was: rcu_sched detected expedited stalls in
 amdgpu after suspend)

On Wed, Jul 06, 2022 at 08:09:49PM +0200, Uladzislau Rezki wrote:
> On Wed, Jul 06, 2022 at 10:58:36AM -0700, Paul E. McKenney wrote:
> > On Wed, Jul 06, 2022 at 07:48:20PM +0200, Uladzislau Rezki wrote:
> > > Hello.
> > > 
> > > On Mon, Jul 04, 2022 at 01:30:50PM +0200, Christian König wrote:
> > > > Hi guys,
> > > > 
> > > > Am 28.06.22 um 22:11 schrieb Uladzislau Rezki:
> > > > > > Excerpts from Paul E. McKenney's message of June 28, 2022 2:54 pm:
> > > > > > > All you need to do to get the previous behavior is to add something like
> > > > > > > this to your defconfig file:
> > > > > > > 
> > > > > > > CONFIG_RCU_EXP_CPU_STALL_TIMEOUT=21000
> > > > > > > 
> > > > > > > Any reason why this will not work for you?
> > > > 
> > > > sorry for jumping in so later, I was on vacation for a week.
> > > > 
> > > > Well when any RCU period is longer than 20ms and amdgpu in the backtrace my
> > > > educated guess is that we messed up some timeout waiting for the hw.
> > > > 
> > > > We usually do wait a few us, but it can be that somebody is waiting for ms
> > > > instead.
> > > > 
> > > > So there are some todos here as far as I can see and It would be helpful to
> > > > get a cleaner backtrace if possible.
> > > > 
> > > Actually CONFIG_ANDROID looks like is going to be removed, so the CONFIG_RCU_EXP_CPU_STALL_TIMEOUT
> > > will not have any dependencies on the CONFIG_ANDROID anymore:
> > > 
> > > https://lkml.org/lkml/2022/6/29/756
> > 
> > But you can set the RCU_EXP_CPU_STALL_TIMEOUT Kconfig option, if you
> > wish.  Setting this option to 20 will get you the behavior previously
> > obtained by setting the now-defunct ANDROID Kconfig option.
> > 
> Right. Or over boot parameter. So for us it is not a big issue :)

Specifically rcupdate.rcu_exp_cpu_stall_timeout, for those just now
tuning in.  ;-)

							Thanx, Paul