Re: [PATCH] [v2]Input: evdev - drop partial events after emptying the buffer

[Peter Hutterer]

On Fri, Jan 08, 2016 at 11:16:49AM +0530, Aniroop Mathur wrote:
> On Fri, Jan 8, 2016 at 10:34 AM, Peter Hutterer
> <peter.hutterer@xxxxxxxxx> wrote:
> > On Mon, Jan 04, 2016 at 09:58:48PM +0530, Aniroop Mathur wrote:
> >> This patch introduces concept to drop partial events in evdev handler
> >> itself after emptying the buffer which are dropped by all evdev
> >> clients in userspace after SYN_DROPPED occurs.
> >> This in turn saves space of partial events in evdev handler buffer
> >> and reduces evdev client reading requests.
> >>
> >> Signed-off-by: Aniroop Mathur <a.mathur@xxxxxxxxxxx>
> >> ---
> >>  drivers/input/evdev.c | 56 ++++++++++++++++++++++++++++++++++++++++++---------
> >>  1 file changed, 47 insertions(+), 9 deletions(-)
> >>
> >> diff --git a/drivers/input/evdev.c b/drivers/input/evdev.c
> >> index e9ae3d5..0a5ead8 100644
> >> --- a/drivers/input/evdev.c
> >> +++ b/drivers/input/evdev.c
> >> @@ -58,6 +58,7 @@ struct evdev_client {
> >>       struct list_head node;
> >>       unsigned int clk_type;
> >>       bool revoked;
> >> +     bool drop_pevent; /* specifies whether partial events need to be dropped */
> >>       unsigned long *evmasks[EV_CNT];
> >>       unsigned int bufsize;
> >>       struct input_event buffer[];
> >> @@ -192,6 +193,7 @@ static int evdev_set_clk_type(struct evdev_client *client, unsigned int clkid)
> >>  {
> >>       unsigned long flags;
> >>       unsigned int clk_type;
> >> +     struct input_event ev;
> >>
> >>       switch (clkid) {
> >>
> >> @@ -218,8 +220,26 @@ static int evdev_set_clk_type(struct evdev_client *client, unsigned int clkid)
> >>               spin_lock_irqsave(&client->buffer_lock, flags);
> >>
> >>               if (client->head != client->tail) {
> >> -                     client->packet_head = client->head = client->tail;
> >> +
> >> +                     /* Store previous event */
> >> +                     client->head--;
> >> +                     client->head &= client->bufsize - 1;
> >> +                     ev = client->buffer[client->head];
> >> +
> >> +                     client->packet_head = client->head = client->tail = 0;
> >>                       __evdev_queue_syn_dropped(client);
> >> +
> >> +                     /*
> >> +                      * If last packet is fully stored, queue SYN_REPORT
> >> +                      * so that clients do not ignore next full packet.
> >> +                      * And if last packet is NOT fully stored,
> >> +                      * set drop_pevent to true to ignore partial events.
> >> +                      */
> >> +                     if (ev.type == EV_SYN && ev.code == SYN_REPORT) {
> >> +                             ev.time = client->buffer[client->head - 1].time;
> >
> > if client->head happens to be 0, your index won't be what it should be :)
> > you need the &= here and again after the next line:
> >
> 
> I have set head to 0 after which syn_dropped is queued,
> so head will be 1 always and hence it seems no need to take
> care of head overflow here as min bufsize is 64.
> 
> >> +                             client->buffer[client->head++] = ev;
> >
> >
> >
> >> +                     } else if (ev.type != EV_SYN && ev.code != SYN_REPORT)
> >> +                             client->drop_pevent = true;
> >>               }
> >>
> >>               spin_unlock_irqrestore(&client->buffer_lock, flags);
> >> @@ -236,17 +256,27 @@ static void __pass_event(struct evdev_client *client,
> >>
> >>       if (unlikely(client->head == client->tail)) {
> >>               /*
> >> -              * This effectively "drops" all unconsumed events, leaving
> >> -              * EV_SYN/SYN_DROPPED plus the newest event in the queue.
> >> +              * This effectively "drops" all unconsumed events, storing
> >> +              * EV_SYN/SYN_DROPPED and the newest event in the queue but
> >> +              * only if it is EV_SYN/SYN_REPORT so that clients can read
> >> +              * the next full event packet. And set drop_pevent to true
> >> +              * if last event packet is not stored completely in buffer
> >> +              * to ignore upcoming partial events.
> >>                */
> >> -             client->tail = (client->head - 2) & (client->bufsize - 1);
> >>
> >> -             client->buffer[client->tail].time = event->time;
> >> -             client->buffer[client->tail].type = EV_SYN;
> >> -             client->buffer[client->tail].code = SYN_DROPPED;
> >> -             client->buffer[client->tail].value = 0;
> >> +             client->tail = client->head = client->packet_head;
> >>
> >> -             client->packet_head = client->tail;
> >> +             client->buffer[client->head].time = event->time;
> >> +             client->buffer[client->head].type = EV_SYN;
> >> +             client->buffer[client->head].code = SYN_DROPPED;
> >> +             client->buffer[client->head].value = 0;
> >> +             client->head = (client->head + 1) & (client->bufsize -1);
> >> +
> >> +             if (event->type == EV_SYN && event->code == SYN_REPORT) {
> >> +                     client->buffer[client->head++] = *event;
> >> +                     client->head &= client->bufsize - 1;
> >> +             } else if (event->type != EV_SYN && event->code != SYN_REPORT)
> >> +                     client->drop_pevent = true;
> >
> > given that this condition is almost exactly the same as above, you should
> > share the code. you should also look into checking whether this can be moved
> > to __evdev_queue_syn_dropped() anyway, it seems like it can with little
> > effort.
> >
> > The protocol itself looks correct now though.
> >
> 
> Thank you Mr. Peter.
> I have already sent the v4 which moved the code to
> __evdev_queue_syn_dropped() function. Please have a look.

aargh. I had both in my inbox and then replied to the wrong version anyway.
sorry.

Cheers,
   Peter

> 
> Regards,
> Aniroop
> 
> > Cheers,
> >    Peter
> >
> >>       }
> >>
> >>       if (event->type == EV_SYN && event->code == SYN_REPORT) {
> >> @@ -284,6 +314,14 @@ static void evdev_pass_values(struct evdev_client *client,
> >>                       wakeup = true;
> >>               }
> >>
> >> +             /* drop partial events of last packet but queue SYN_REPORT */
> >> +             if (client->drop_pevent) {
> >> +                     if (v->type == EV_SYN && v->code == SYN_REPORT)
> >> +                             client->drop_pevent = false;
> >> +                     else
> >> +                             continue;
> >> +             }
> >> +
> >>               event.type = v->type;
> >>               event.code = v->code;
> >>               event.value = v->value;
> >> --
> >> 2.6.2
> >>