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

[Aniroop Mathur]

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.

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
>>