Date:   Thu, 23 Jul 2020 19:06:18 -0700
From:   Badhri Jagan Sridharan <badhri@...gle.com>
To:     Guenter Roeck <linux@...ck-us.net>
Cc:     Heikki Krogerus <heikki.krogerus@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        USB <linux-usb@...r.kernel.org>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] usb: typec: tcpm: Migrate workqueue to RT priority for
 processing events

Thanks Guenter ! Yes I missed the fact that hrtimer_start actually
restarts the timer automatically if needed. So, the call to
hrtimer_cancel is redundant and I have updated the patch and retested
it.

On Thu, Jul 23, 2020 at 8:40 AM Guenter Roeck <linux@...ck-us.net> wrote:
>
> On Wed, Jul 22, 2020 at 11:15:24PM -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@...gle.com>
> > ---
> >  drivers/usb/typec/tcpm/tcpm.c | 138 ++++++++++++++++++++++------------
> >  1 file changed, 90 insertions(+), 48 deletions(-)
> >
> > diff --git a/drivers/usb/typec/tcpm/tcpm.c b/drivers/usb/typec/tcpm/tcpm.c
> > index ff1cbd2147ca8a..0dcab6f08f8587 100644
> > --- a/drivers/usb/typec/tcpm/tcpm.c
> > +++ b/drivers/usb/typec/tcpm/tcpm.c
> > @@ -8,8 +8,10 @@
> >  #include <linux/completion.h>
> >  #include <linux/debugfs.h>
> >  #include <linux/device.h>
> > +#include <linux/hrtimer.h>
> >  #include <linux/jiffies.h>
> >  #include <linux/kernel.h>
> > +#include <linux/kthread.h>
> >  #include <linux/module.h>
> >  #include <linux/mutex.h>
> >  #include <linux/power_supply.h>
> > @@ -28,7 +30,8 @@
> >  #include <linux/usb/role.h>
> >  #include <linux/usb/tcpm.h>
> >  #include <linux/usb/typec_altmode.h>
> > -#include <linux/workqueue.h>
> > +
> > +#include <uapi/linux/sched/types.h>
> >
> >  #define FOREACH_STATE(S)                     \
> >       S(INVALID_STATE),                       \
> > @@ -195,7 +198,7 @@ struct tcpm_port {
> >       struct device *dev;
> >
> >       struct mutex lock;              /* tcpm state machine lock */
> > -     struct workqueue_struct *wq;
> > +     struct kthread_worker *wq;
> >
> >       struct typec_capability typec_caps;
> >       struct typec_port *typec_port;
> > @@ -239,15 +242,17 @@ struct tcpm_port {
> >       enum tcpm_state prev_state;
> >       enum tcpm_state state;
> >       enum tcpm_state delayed_state;
> > -     unsigned long delayed_runtime;
> > +     ktime_t delayed_runtime;
> >       unsigned long delay_ms;
> >
> >       spinlock_t pd_event_lock;
> >       u32 pd_events;
> >
> > -     struct work_struct event_work;
> > -     struct delayed_work state_machine;
> > -     struct delayed_work vdm_state_machine;
> > +     struct kthread_work event_work;
> > +     struct hrtimer state_machine_timer;
> > +     struct kthread_work state_machine;
> > +     struct hrtimer vdm_state_machine_timer;
> > +     struct kthread_work vdm_state_machine;
> >       bool state_machine_running;
> >
> >       struct completion tx_complete;
> > @@ -332,7 +337,7 @@ struct tcpm_port {
> >  };
> >
> >  struct pd_rx_event {
> > -     struct work_struct work;
> > +     struct kthread_work work;
> >       struct tcpm_port *port;
> >       struct pd_message msg;
> >  };
> > @@ -906,6 +911,25 @@ static int tcpm_pd_send_sink_caps(struct tcpm_port *port)
> >       return tcpm_pd_transmit(port, TCPC_TX_SOP, &msg);
> >  }
> >
> > +static void mod_tcpm_delayed_work(struct tcpm_port *port, unsigned int delay_ms)
> > +{
> > +     hrtimer_cancel(&port->state_machine_timer);
> > +     if (delay_ms)
> > +             hrtimer_start(&port->state_machine_timer, ms_to_ktime(delay_ms), HRTIMER_MODE_REL);
> > +     else
> > +             kthread_queue_work(port->wq, &port->state_machine);
>
> If I understand correctly, hrtimer_start() restarts an already running timer.
> With this in mind, would the following be more efficient ?
>
>         if (delay_ms) {
>                 hrtimer_start(&port->state_machine_timer, ms_to_ktime(delay_ms), HRTIMER_MODE_REL);
>         } else {
>                 hrtimer_cancel(&port->state_machine_timer);
>                 kthread_queue_work(port->wq, &port->state_machine);
>         }
>
> Thanks,
> Guenter
>
> > +}
> > +
> > +static void mod_vdm_delayed_work(struct tcpm_port *port, unsigned int delay_ms)
> > +{
> > +     hrtimer_cancel(&port->vdm_state_machine_timer);
> > +     if (delay_ms)
> > +             hrtimer_start(&port->vdm_state_machine_timer, ms_to_ktime(delay_ms),
> > +                           HRTIMER_MODE_REL);
> > +     else
> > +             kthread_queue_work(port->wq, &port->vdm_state_machine);
> > +}
> > +
> >  static void tcpm_set_state(struct tcpm_port *port, enum tcpm_state state,
> >                          unsigned int delay_ms)
> >  {
> > @@ -914,9 +938,8 @@ static void tcpm_set_state(struct tcpm_port *port, enum tcpm_state state,
> >                        tcpm_states[port->state], tcpm_states[state],
> >                        delay_ms);
> >               port->delayed_state = state;
> > -             mod_delayed_work(port->wq, &port->state_machine,
> > -                              msecs_to_jiffies(delay_ms));
> > -             port->delayed_runtime = jiffies + msecs_to_jiffies(delay_ms);
> > +             mod_tcpm_delayed_work(port, delay_ms);
> > +             port->delayed_runtime = ktime_add(ktime_get(), ms_to_ktime(delay_ms));
> >               port->delay_ms = delay_ms;
> >       } else {
> >               tcpm_log(port, "state change %s -> %s",
> > @@ -931,7 +954,7 @@ static void tcpm_set_state(struct tcpm_port *port, enum tcpm_state state,
> >                * machine.
> >                */
> >               if (!port->state_machine_running)
> > -                     mod_delayed_work(port->wq, &port->state_machine, 0);
> > +                     mod_tcpm_delayed_work(port, 0);
> >       }
> >  }
> >
> > @@ -952,7 +975,7 @@ static void tcpm_queue_message(struct tcpm_port *port,
> >                              enum pd_msg_request message)
> >  {
> >       port->queued_message = message;
> > -     mod_delayed_work(port->wq, &port->state_machine, 0);
> > +     mod_tcpm_delayed_work(port, 0);
> >  }
> >
> >  /*
> > @@ -1238,8 +1261,7 @@ static void tcpm_handle_vdm_request(struct tcpm_port *port,
> >                       port->vdm_state = VDM_STATE_WAIT_RSP_BUSY;
> >                       port->vdo_retry = (p0 & ~VDO_CMDT_MASK) |
> >                               CMDT_INIT;
> > -                     mod_delayed_work(port->wq, &port->vdm_state_machine,
> > -                                      msecs_to_jiffies(PD_T_VDM_BUSY));
> > +                     mod_vdm_delayed_work(port, PD_T_VDM_BUSY);
> >                       return;
> >               }
> >               port->vdm_state = VDM_STATE_DONE;
> > @@ -1250,7 +1272,7 @@ static void tcpm_handle_vdm_request(struct tcpm_port *port,
> >
> >       if (rlen > 0) {
> >               tcpm_queue_vdm(port, response[0], &response[1], rlen - 1);
> > -             mod_delayed_work(port->wq, &port->vdm_state_machine, 0);
> > +             mod_vdm_delayed_work(port, 0);
> >       }
> >  }
> >
> > @@ -1267,7 +1289,7 @@ static void tcpm_send_vdm(struct tcpm_port *port, u32 vid, int cmd,
> >                       1 : (PD_VDO_CMD(cmd) <= CMD_ATTENTION), cmd);
> >       tcpm_queue_vdm(port, header, data, count);
> >
> > -     mod_delayed_work(port->wq, &port->vdm_state_machine, 0);
> > +     mod_vdm_delayed_work(port, 0);
> >  }
> >
> >  static unsigned int vdm_ready_timeout(u32 vdm_hdr)
> > @@ -1334,8 +1356,7 @@ static void vdm_run_state_machine(struct tcpm_port *port)
> >                       port->vdm_retries = 0;
> >                       port->vdm_state = VDM_STATE_BUSY;
> >                       timeout = vdm_ready_timeout(port->vdo_data[0]);
> > -                     mod_delayed_work(port->wq, &port->vdm_state_machine,
> > -                                      timeout);
> > +                     mod_vdm_delayed_work(port, timeout);
> >               }
> >               break;
> >       case VDM_STATE_WAIT_RSP_BUSY:
> > @@ -1364,10 +1385,9 @@ static void vdm_run_state_machine(struct tcpm_port *port)
> >       }
> >  }
> >
> > -static void vdm_state_machine_work(struct work_struct *work)
> > +static void vdm_state_machine_work(struct kthread_work *work)
> >  {
> > -     struct tcpm_port *port = container_of(work, struct tcpm_port,
> > -                                           vdm_state_machine.work);
> > +     struct tcpm_port *port = container_of(work, struct tcpm_port, vdm_state_machine);
> >       enum vdm_states prev_state;
> >
> >       mutex_lock(&port->lock);
> > @@ -1515,7 +1535,7 @@ static int tcpm_altmode_enter(struct typec_altmode *altmode, u32 *vdo)
> >       header |= VDO_OPOS(altmode->mode);
> >
> >       tcpm_queue_vdm(port, header, vdo, vdo ? 1 : 0);
> > -     mod_delayed_work(port->wq, &port->vdm_state_machine, 0);
> > +     mod_vdm_delayed_work(port, 0);
> >       mutex_unlock(&port->lock);
> >
> >       return 0;
> > @@ -1531,7 +1551,7 @@ static int tcpm_altmode_exit(struct typec_altmode *altmode)
> >       header |= VDO_OPOS(altmode->mode);
> >
> >       tcpm_queue_vdm(port, header, NULL, 0);
> > -     mod_delayed_work(port->wq, &port->vdm_state_machine, 0);
> > +     mod_vdm_delayed_work(port, 0);
> >       mutex_unlock(&port->lock);
> >
> >       return 0;
> > @@ -1544,7 +1564,7 @@ static int tcpm_altmode_vdm(struct typec_altmode *altmode,
> >
> >       mutex_lock(&port->lock);
> >       tcpm_queue_vdm(port, header, data, count - 1);
> > -     mod_delayed_work(port->wq, &port->vdm_state_machine, 0);
> > +     mod_vdm_delayed_work(port, 0);
> >       mutex_unlock(&port->lock);
> >
> >       return 0;
> > @@ -1961,7 +1981,7 @@ static void tcpm_pd_ext_msg_request(struct tcpm_port *port,
> >       }
> >  }
> >
> > -static void tcpm_pd_rx_handler(struct work_struct *work)
> > +static void tcpm_pd_rx_handler(struct kthread_work *work)
> >  {
> >       struct pd_rx_event *event = container_of(work,
> >                                                struct pd_rx_event, work);
> > @@ -2023,10 +2043,10 @@ void tcpm_pd_receive(struct tcpm_port *port, const struct pd_message *msg)
> >       if (!event)
> >               return;
> >
> > -     INIT_WORK(&event->work, tcpm_pd_rx_handler);
> > +     kthread_init_work(&event->work, tcpm_pd_rx_handler);
> >       event->port = port;
> >       memcpy(&event->msg, msg, sizeof(*msg));
> > -     queue_work(port->wq, &event->work);
> > +     kthread_queue_work(port->wq, &event->work);
> >  }
> >  EXPORT_SYMBOL_GPL(tcpm_pd_receive);
> >
> > @@ -2079,9 +2099,9 @@ static bool tcpm_send_queued_message(struct tcpm_port *port)
> >       } while (port->queued_message != PD_MSG_NONE);
> >
> >       if (port->delayed_state != INVALID_STATE) {
> > -             if (time_is_after_jiffies(port->delayed_runtime)) {
> > -                     mod_delayed_work(port->wq, &port->state_machine,
> > -                                      port->delayed_runtime - jiffies);
> > +             if (ktime_after(port->delayed_runtime, ktime_get())) {
> > +                     mod_tcpm_delayed_work(port, ktime_to_ms(ktime_sub(port->delayed_runtime,
> > +                                                                       ktime_get())));
> >                       return true;
> >               }
> >               port->delayed_state = INVALID_STATE;
> > @@ -3214,10 +3234,9 @@ static void run_state_machine(struct tcpm_port *port)
> >       case SNK_DISCOVERY_DEBOUNCE_DONE:
> >               if (!tcpm_port_is_disconnected(port) &&
> >                   tcpm_port_is_sink(port) &&
> > -                 time_is_after_jiffies(port->delayed_runtime)) {
> > +                 ktime_after(port->delayed_runtime, ktime_get())) {
> >                       tcpm_set_state(port, SNK_DISCOVERY,
> > -                                    jiffies_to_msecs(port->delayed_runtime -
> > -                                                     jiffies));
> > +                                    ktime_to_ms(ktime_sub(port->delayed_runtime, ktime_get())));
> >                       break;
> >               }
> >               tcpm_set_state(port, unattached_state(port), 0);
> > @@ -3612,10 +3631,9 @@ static void run_state_machine(struct tcpm_port *port)
> >       }
> >  }
> >
> > -static void tcpm_state_machine_work(struct work_struct *work)
> > +static void tcpm_state_machine_work(struct kthread_work *work)
> >  {
> > -     struct tcpm_port *port = container_of(work, struct tcpm_port,
> > -                                           state_machine.work);
> > +     struct tcpm_port *port = container_of(work, struct tcpm_port, state_machine);
> >       enum tcpm_state prev_state;
> >
> >       mutex_lock(&port->lock);
> > @@ -3975,7 +3993,7 @@ static void _tcpm_pd_hard_reset(struct tcpm_port *port)
> >                      0);
> >  }
> >
> > -static void tcpm_pd_event_handler(struct work_struct *work)
> > +static void tcpm_pd_event_handler(struct kthread_work *work)
> >  {
> >       struct tcpm_port *port = container_of(work, struct tcpm_port,
> >                                             event_work);
> > @@ -4016,7 +4034,7 @@ void tcpm_cc_change(struct tcpm_port *port)
> >       spin_lock(&port->pd_event_lock);
> >       port->pd_events |= TCPM_CC_EVENT;
> >       spin_unlock(&port->pd_event_lock);
> > -     queue_work(port->wq, &port->event_work);
> > +     kthread_queue_work(port->wq, &port->event_work);
> >  }
> >  EXPORT_SYMBOL_GPL(tcpm_cc_change);
> >
> > @@ -4025,7 +4043,7 @@ void tcpm_vbus_change(struct tcpm_port *port)
> >       spin_lock(&port->pd_event_lock);
> >       port->pd_events |= TCPM_VBUS_EVENT;
> >       spin_unlock(&port->pd_event_lock);
> > -     queue_work(port->wq, &port->event_work);
> > +     kthread_queue_work(port->wq, &port->event_work);
> >  }
> >  EXPORT_SYMBOL_GPL(tcpm_vbus_change);
> >
> > @@ -4034,7 +4052,7 @@ void tcpm_pd_hard_reset(struct tcpm_port *port)
> >       spin_lock(&port->pd_event_lock);
> >       port->pd_events = TCPM_RESET_EVENT;
> >       spin_unlock(&port->pd_event_lock);
> > -     queue_work(port->wq, &port->event_work);
> > +     kthread_queue_work(port->wq, &port->event_work);
> >  }
> >  EXPORT_SYMBOL_GPL(tcpm_pd_hard_reset);
> >
> > @@ -4742,10 +4760,28 @@ static int devm_tcpm_psy_register(struct tcpm_port *port)
> >       return PTR_ERR_OR_ZERO(port->psy);
> >  }
> >
> > +static enum hrtimer_restart state_machine_timer_handler(struct hrtimer *timer)
> > +{
> > +     struct tcpm_port *port = container_of(timer, struct tcpm_port, state_machine_timer);
> > +
> > +     kthread_queue_work(port->wq, &port->state_machine);
> > +     return HRTIMER_NORESTART;
> > +}
> > +
> > +static enum hrtimer_restart vdm_state_machine_timer_handler(struct hrtimer *timer)
> > +{
> > +     struct tcpm_port *port = container_of(timer, struct tcpm_port, vdm_state_machine_timer);
> > +
> > +     kthread_queue_work(port->wq, &port->vdm_state_machine);
> > +     return HRTIMER_NORESTART;
> > +}
> > +
> >  struct tcpm_port *tcpm_register_port(struct device *dev, struct tcpc_dev *tcpc)
> >  {
> >       struct tcpm_port *port;
> >       int err;
> > +     /* Priority just lower than default irq thread priority */
> > +     struct sched_param param = {.sched_priority = (MAX_USER_RT_PRIO / 2) + 1,};
> >
> >       if (!dev || !tcpc ||
> >           !tcpc->get_vbus || !tcpc->set_cc || !tcpc->get_cc ||
> > @@ -4763,12 +4799,18 @@ struct tcpm_port *tcpm_register_port(struct device *dev, struct tcpc_dev *tcpc)
> >       mutex_init(&port->lock);
> >       mutex_init(&port->swap_lock);
> >
> > -     port->wq = create_singlethread_workqueue(dev_name(dev));
> > -     if (!port->wq)
> > -             return ERR_PTR(-ENOMEM);
> > -     INIT_DELAYED_WORK(&port->state_machine, tcpm_state_machine_work);
> > -     INIT_DELAYED_WORK(&port->vdm_state_machine, vdm_state_machine_work);
> > -     INIT_WORK(&port->event_work, tcpm_pd_event_handler);
> > +     port->wq = kthread_create_worker(0, dev_name(dev));
> > +     if (IS_ERR(port->wq))
> > +             return (struct tcpm_port *)port->wq;
> > +     sched_setscheduler(port->wq->task, SCHED_FIFO, &param);
> > +
> > +     kthread_init_work(&port->state_machine, tcpm_state_machine_work);
> > +     kthread_init_work(&port->vdm_state_machine, vdm_state_machine_work);
> > +     kthread_init_work(&port->event_work, tcpm_pd_event_handler);
> > +     hrtimer_init(&port->state_machine_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> > +     port->state_machine_timer.function = state_machine_timer_handler;
> > +     hrtimer_init(&port->vdm_state_machine_timer, CLOCK_MONOTONIC, HRTIMER_MODE_REL);
> > +     port->vdm_state_machine_timer.function = vdm_state_machine_timer_handler;
> >
> >       spin_lock_init(&port->pd_event_lock);
> >
> > @@ -4820,7 +4862,7 @@ struct tcpm_port *tcpm_register_port(struct device *dev, struct tcpc_dev *tcpc)
> >       usb_role_switch_put(port->role_sw);
> >  out_destroy_wq:
> >       tcpm_debugfs_exit(port);
> > -     destroy_workqueue(port->wq);
> > +     kthread_destroy_worker(port->wq);
> >       return ERR_PTR(err);
> >  }
> >  EXPORT_SYMBOL_GPL(tcpm_register_port);
> > @@ -4835,7 +4877,7 @@ void tcpm_unregister_port(struct tcpm_port *port)
> >       typec_unregister_port(port->typec_port);
> >       usb_role_switch_put(port->role_sw);
> >       tcpm_debugfs_exit(port);
> > -     destroy_workqueue(port->wq);
> > +     kthread_destroy_worker(port->wq);
> >  }
> >  EXPORT_SYMBOL_GPL(tcpm_unregister_port);
> >
> > --
> > 2.28.0.rc0.105.gf9edc3c819-goog
> >

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