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

Greg Kroah-Hartman
2020-07-30T06:44:08Z

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