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From:   Badhri Jagan Sridharan <badhri@google.com>
Date:   Wed, 22 Jul 2020 23:20:48 -0700
Message-ID: <CAPTae5KZKKFhgovg1jGwyWhSQ-gfdXDsKUL+yFNxqkq27VK49g@mail.gmail.com>
Subject: Re: [PATCH] usb: typec: tcpm: Move to high priority workqueue for
 processing events
To:     Guenter Roeck <linux@roeck-us.net>
Cc:     reg Kroah-Hartman <gregkh@linuxfoundation.org>,
        Heikki Krogerus <heikki.krogerus@linux.intel.com>,
        USB <linux-usb@vger.kernel.org>,
        LKML <linux-kernel@vger.kernel.org>
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Hi Guenter,

Just sent out the patch "usb: typec: tcpm: Migrate workqueue to RT
priority for processing events" which uses kthread_create_worker and
hrtimer.nAppreciate your guidance !! The commits 38a1222ae4f3 and
1ff688209e2e were spot on as they were trying solve the same problem
in a different subsystem.

Thanks,
Badhri

On Tue, Jul 14, 2020 at 10:16 AM Badhri Jagan Sridharan
<badhri@google.com> wrote:
>
> On Mon, Jul 13, 2020 at 11:58 PM Guenter Roeck <linux@roeck-us.net> wrote=
:
> >
> > On 7/13/20 11:05 PM, reg Kroah-Hartman wrote:
> > > On Mon, Jul 13, 2020 at 01:43:00PM -0700, Badhri Jagan Sridharan wrot=
e:
> > >> "tReceiverResponse 15 ms Section 6.6.2
> > >> The receiver of a Message requiring a response Shall respond
> > >> within tReceiverResponse in order to ensure that the
> > >> sender=E2=80=99s SenderResponseTimer does not expire."
> > >>
> > >> When the cpu complex is busy running other lower priority
> > >> work items, TCPM's work queue sometimes does not get scheduled
> > >> on time to meet the above requirement from the spec.
> > >> Elevating the TCPM's work queue to higher priority allows
> > >> TCPM to meet tReceiverResponse in a busy system.
> > >>
> > >> Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > >> ---
> > >>  drivers/usb/typec/tcpm/tcpm.c | 2 +-
> > >>  1 file changed, 1 insertion(+), 1 deletion(-)
> > >>
> > >> diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/=
tcpm.c
> > >> index 82b19ebd7838e0..088b6f1fa1ff89 100644
> > >> --- a/drivers/usb/typec/tcpm/tcpm.c
> > >> +++ b/drivers/usb/typec/tcpm/tcpm.c
> > >> @@ -4747,7 +4747,7 @@ struct tcpm_port *tcpm_register_port(struct de=
vice *dev, struct tcpc_dev *tcpc)
> > >>      mutex_init(&port->lock);
> > >>      mutex_init(&port->swap_lock);
> > >>
> > >> -    port->wq =3D create_singlethread_workqueue(dev_name(dev));
> > >> +    port->wq =3D alloc_ordered_workqueue("%s", WQ_HIGHPRI, dev_name=
(dev));
> > >
> > > How are you "guaranteeing" that this is really going to change anythi=
ng
> > > on a highly loaded machine?
> > >
> > > Yes, it might make things better, but if you have a hard deadline lik=
e
> > > this, you need to do things a bit differently to always ensure that y=
ou
> > > meet it.  I do not think this change is that fix, do you?
> > >
> Yes Greg I agree with you, moving to HIGHPRI was making it better but
> is not going to
> solve the problem always. I was wondering whether are there better
> ways of doing this.
>
> >
> > Good point. The worker in drivers/watchdog/ !watchdog_dev.c might be
> > useful as a starting point. There may be better examples - this is
> > just one I know of which had a similar problem. See commits
> > 38a1222ae4f3 and 1ff688209e2e.
> >
> > Guenter
>
> Thanks a lot Guenter !! Very useful pointers, will review the
> approaches in both the
> commits !