Re: [PATCH v3] usb: typec: tcpm: Migrate workqueue to RT priority for processing events

Badhri Jagan Sridharan
2020-07-30T07:29:04Z

Hi Greg,

Yes Guenter's suspicion is right. Mine was conflicting with Han's
following patch:
commit 5f2b8d87bca528616e04344d1fc4032dc5ec0f3d
Author: Hans de Goede <hdegoede@redhat.com>
Date: Fri Jul 24 19:46:57 2020 +0200

usb: typec: tcpm: Move mod_delayed_work(&port->vdm_state_machine)
call into tcpm_queue_vdm()

All callers of tcpm_queue_vdm() immediately follow the tcpm_queue_vdm()
vdm call with a:

mod_delayed_work(port->wq, &port->vdm_state_machine, 0);

Call, fold this into tcpm_queue_vdm() itself.

Reviewed-by: Guenter Roeck <linux@roeck-us.net>
Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
Signed-off-by: Hans de Goede <hdegoede@redhat.com>
Link: https://lore.kernel.org/r/20200724174702.61754-1-hdegoede@redhat.com
Signed-off-by: Greg Kroah-Hartman <gregkh@linuxfoundation.org>

Fixed merged conflicts and sent out the v4 version of the patch.
Added hdegoede@redhat.com to CC as well.

Thanks,
Badhri

On Wed, Jul 29, 2020 at 11:44 PM Greg Kroah-Hartman
<gregkh@linuxfoundation.org> wrote:
>
> On Wed, Jul 29, 2020 at 07:24:57PM -0700, Badhri Jagan Sridharan wrote:
> > "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’s 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.
> > Moving to kthread_work apis to run with real time priority.
> > Just lower than the default threaded irq priority,
> > MAX_USER_RT_PRIO/2 + 1. (Higher number implies lower priority).
> >
> > Further, as observed in 1ff688209e2e, moving to hrtimers to
> > overcome scheduling latency while scheduling the delayed work.
> >
> > TCPM has three work streams:
> > 1. tcpm_state_machine
> > 2. vdm_state_machine
> > 3. event_work
> >
> > tcpm_state_machine and vdm_state_machine both schedule work in
> > future i.e. delayed. Hence each of them have a corresponding
> > hrtimer, tcpm_state_machine_timer & vdm_state_machine_timer.
> >
> > When work is queued right away kthread_queue_work is used.
> > Else, the relevant timer is programmed and made to queue
> > the kthread_work upon timer expiry.
> >
> > kthread_create_worker only creates one kthread worker thread,
> > hence single threadedness of workqueue is retained.
> >
> > Signed-off-by: Badhri Jagan Sridharan <badhri@google.com>
> > Reviewed-by: Guenter Roeck <linux@roeck-us.net>
> > Reviewed-by: Heikki Krogerus <heikki.krogerus@linux.intel.com>
> > ---
> > Changes since v1:(Guenter's suggestions)
> > - Remove redundant call to hrtimer_cancel while calling
> > hrtimer_start.
> >
> > Changes since v2:(Greg KH's suggestions)
> > - Rebase usb-next TOT.
> > 633198cd2945b7 (HEAD -> usb-next-1) usb: typec: tcpm: Migrate workqueue to RT priority for processing events
> > fa56dd9152ef95 (origin/usb-next) Merge tag 'usb-serial-5.9-rc1' of https://git.kernel.org/pub/scm/linux/kernel/git/johan/usb-serial into usb-next
> > 25252919a1050e xhci: dbgtty: Make some functions static
> > b0e02550346e67 xhci: dbc: Make function xhci_dbc_ring_alloc() static
> > ca6377900974c3 Revert "usb: dwc2: override PHY input signals with usb role switch support"
> > 09df709cb5aeb2 Revert "usb: dwc2: don't use ID/Vbus detection if usb-role-switch on STM32MP15 SoCs"
> > 17a82716587e9d USB: iowarrior: fix up report size handling for some devices
> > e98ba8cc3f8a89 Merge tag 'usb-for-v5.9' of git://git.kernel.org/pub/scm/linux/kernel/git/balbi/usb into usb-next
> > c97793089b11f7 Merge 5.8-rc7 into usb-next
> > 92ed301919932f (tag: v5.8-rc7, origin/usb-linus, origin/main) Linux 5.8-rc7
> >
>
> Hm, still does not apply. I think it has something to do with other
> patches that landed before yours, can you rebase again?
>
> thanks,
>
> greg k-h