[igt-dev] [Intel-gfx] [PATCH i-g-t 2/3] lib: Align ring measurement to timer

[Antonio Argenziano]

On 30/05/18 03:33, Chris Wilson wrote:
> After hitting the SIGINT from execbuf, wait until the next timer signal
> before trying again. This aligns the start of the ioctl to the timer,
> hopefully maximising the amount of time we have for processing before
> the next signal -- trying to prevent the case where we are scheduled out
> in the middle of processing and so hit the timer signal too early.
> 
> References: https://bugs.freedesktop.org/show_bug.cgi?id=106695
> Signed-off-by: Chris Wilson <chris at chris-wilson.co.uk>

Not sure I understand what is the sequence of events, is the problem we 
get a signal in the middle of a 'good' execbuf and exit the while loop 
prematurely? If so maybe we can also think of making the timer 'VIRTUAL' 
so that it would decrement only when the process is executing.

Thanks,
Antonio

> ---
>   lib/i915/gem_ring.c | 2 ++
>   1 file changed, 2 insertions(+)
> 
> diff --git a/lib/i915/gem_ring.c b/lib/i915/gem_ring.c
> index 7d64165eb..0c061000c 100644
> --- a/lib/i915/gem_ring.c
> +++ b/lib/i915/gem_ring.c
> @@ -96,6 +96,8 @@ __gem_measure_ring_inflight(int fd, unsigned int engine, enum measure_ring_flags
>   		if (last == count)
>   			break;
>   
> +		/* sleep until the next timer interrupt (woken on signal) */
> +		pause();

Does it cause any (sensible) slowdown?

Thanks,
Antonio

>   		last = count;
>   	} while (1);
>   
>