Re: [PATCH v5 04/21] gpu: host1x: Remove cancelled waiters immediately

Mikko Perttunen
2021-01-12T22:23:14Z

On 1/13/21 12:07 AM, Dmitry Osipenko wrote:
> 11.01.2021 16:00, Mikko Perttunen пишет:
>> -void host1x_intr_put_ref(struct host1x *host, unsigned int id, void *ref)
>> +void host1x_intr_put_ref(struct host1x *host, unsigned int id, void *ref,
>> + bool flush)
>> {
>> struct host1x_waitlist *waiter = ref;
>> struct host1x_syncpt *syncpt;
>>
>> - while (atomic_cmpxchg(&waiter->state, WLS_PENDING, WLS_CANCELLED) ==
>> - WLS_REMOVED)
>> - schedule();
>> + atomic_cmpxchg(&waiter->state, WLS_PENDING, WLS_CANCELLED);
>>
>> syncpt = host->syncpt + id;
>> - (void)process_wait_list(host, syncpt,
>> - host1x_syncpt_load(host->syncpt + id));
>> +
>> + spin_lock(&syncpt->intr.lock);
>> + if (atomic_cmpxchg(&waiter->state, WLS_CANCELLED, WLS_HANDLED) ==
>> + WLS_CANCELLED) {
>> + list_del(&waiter->list);
>> + kref_put(&waiter->refcount, waiter_release);
>> + }
>> + spin_unlock(&syncpt->intr.lock);
>> +
>> + if (flush) {
>> + /* Wait until any concurrently executing handler has finished. */
>> + while (atomic_read(&waiter->state) != WLS_HANDLED)
>> + cpu_relax();
>> + }
>
> A busy-loop shouldn't be used in kernel unless there is a very good
> reason. The wait_event() should be used instead.
>
> But please don't hurry to update this patch, we may need or want to
> retire the host1x-waiter and then these all waiter-related patches won't
> be needed.
>

Yes, we should improve the intr code to remove all this complexity. But
let's merge this first to get a functional baseline and do larger design
changes in follow-up patches.

It is cumbersome for me to develop further series (of which I have
several under work and planning) with this baseline series not being
merged. The uncertainty on the approval of the UAPI design also makes it
hard to know whether it makes sense for me to work on top of this code
or not, so I'd like to focus on what's needed to get this merged instead
of further redesign of the driver at this time.

Mikko