linux-kernel - Re: [PATCH] remoteproc: Create a separate workqueue for recovery tasks

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Date:   Mon, 21 Dec 2020 18:35:39 -0600
From:   Bjorn Andersson <bjorn.andersson@...aro.org>
To:     Alex Elder <elder@...aro.org>
Cc:     rishabhb@...eaurora.org, linux-remoteproc@...r.kernel.org,
        linux-kernel@...r.kernel.org, tsoni@...eaurora.org,
        psodagud@...eaurora.org, sidgup@...eaurora.org
Subject: Re: [PATCH] remoteproc: Create a separate workqueue for recovery
 tasks

On Thu 17 Dec 12:49 CST 2020, Alex Elder wrote:

> On 12/17/20 12:21 PM, rishabhb@...eaurora.org wrote:
> > On 2020-12-17 08:12, Alex Elder wrote:
> > > On 12/15/20 4:55 PM, Bjorn Andersson wrote:
> > > > On Sat 12 Dec 14:48 CST 2020, Rishabh Bhatnagar wrote:
> > > > 
> > > > > Create an unbound high priority workqueue for recovery tasks.
> > > 
> > > I have been looking at a different issue that is caused by
> > > crash notification.
> > > 
> > > What happened was that the modem crashed while the AP was
> > > in system suspend (or possibly even resuming) state.  And
> > > there is no guarantee that the system will have called a
> > > driver's ->resume callback when the crash notification is
> > > delivered.
> > > 
> > > In my case (in the IPA driver), handling a modem crash
> > > cannot be done while the driver is suspended; i.e. the
> > > activities in its ->resume callback must be completed
> > > before we can recover from the crash.
> > > 
> > > For this reason I might like to change the way the
> > > crash notification is handled, but what I'd rather see
> > > is to have the work queue not run until user space
> > > is unfrozen, which would guarantee that all drivers
> > > that have registered for a crash notification will
> > > be resumed when the notification arrives.
> > > 
> > > I'm not sure how that interacts with what you are
> > > looking for here.  I think the workqueue could still
> > > be unbound, but its work would be delayed longer before
> > > any notification (and recovery) started.
> > > 
> > >                     -Alex
> > > 
> > > 
> > In that case, maybe adding a "WQ_FREEZABLE" flag might help?
> 
> Yes, exactly.  But how does that affect whatever you were
> trying to do with your patch?
> 

I don't see any impact on Rishabh's change in particular, syntactically
it would just be a matter of adding another flag and the impact would be
separate from his patch.

In other words, creating a separate work queue to get the long running
work off the system_wq and making sure that these doesn't run during
suspend & resume seems very reasonable to me.

The one piece that I'm still contemplating is the HIPRIO, I would like
to better understand the actual impact - or perhaps is this a result of
everyone downstream moving all their work to HIPRIO work queues,
starving the recovery?

Regards,
Bjorn