Re: [PATCH] reservation: wait only with non-zero timeout specified (v3)

[Maarten Lankhorst <maarten.lankhorst@canonical.com>]

Op 13-01-15 om 10:22 schreef Christian König:
> Am 13.01.2015 um 10:04 schrieb Maarten Lankhorst:
>> Op 13-01-15 om 10:36 schreef Jammy Zhou:
>>> When the timeout value passed to reservation_object_wait_timeout_rcu
>>> is zero, no wait should be done if the fences are not signaled.
>>>
>>> Return '1' for idle and '0' for busy if the specified timeout is '0'
>>> to keep consistent with the case of non-zero timeout.
>>>
>>> v2: call fence_put if not signaled in the case of timeout==0
>>>
>>>
>> Looks more sane, but where do you need this?
>
> The rational is that we want a single function to call from the driver no matter what timeout we have and get a zero if the call timed out and a non zero value otherwise.
>
> When we called reservation_object_wait_timeout_rcu with a timeout of zero we got a return value of zero as well independent of whether or not the fences were signaled. That behavior looked inconsistent and Jammy is trying to fix this with this patch.
>
> We could of course do the check in the calling code as well, but to me it rather looked like the calling convention of reservation_object_wait_timeout_rcu should be thought over one more time.
>
> Either calling it with timeout=0 is invalid and the driver needs to call reservation_object_test_signaled_rcu directly instead or we apply this patch or something similar to get an useful behavior in the case of timeout=0.
I think it would be best to leave timeout=0 returning 0. Not handling it differently gives the same semantics as used by fence_wait_time and wait_event_timeout.
Are there really many cases in which you don't know if timeout = 0 before or not?

~Maarten

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