On Thu, 18 Oct 2018 14:28:47 +0200, Timo Wischer wrote:
On 10/18/18 14:02, Takashi Iwai wrote:
On Thu, 18 Oct 2018 13:33:24 +0200, twischer@de.adit-jv.com wrote:
From: Timo Wischer twischer@de.adit-jv.com
Without this change an interval of (x x+1] will be interpreted as an empty interval but the right value would be x+1. This leads to a failing snd_pcm_hw_params() call which returns -EINVAL.
An example issue log is given in the following: snd_pcm_hw_params failed with err -22 (Invalid argument) ACCESS: MMAP_NONINTERLEAVED FORMAT: S16_LE SUBFORMAT: STD SAMPLE_BITS: 16 FRAME_BITS: 16 CHANNELS: 1 RATE: 16000 PERIOD_TIME: (15999 16000] PERIOD_SIZE: (255 256] PERIOD_BYTES: (510 512] PERIODS: [2 3) BUFFER_TIME: 32000 BUFFER_SIZE: 512 BUFFER_BYTES: 1024
In case of (x x+1) we have to interpret it anyway as a single value of x to compensate rounding issues. For example the period size will result in an interval of (352 353) when the period time is 16ms and the sample rate 22050 Hz (16ms * 22,05 kHz = 352,8 frames). But 352 has to be chosen to allow a buffer size of 705 (32ms * 22,05 kHz = 705,6 frames) which has to be >= 2x period size to avoid Xruns. The buffer size will not end up with an interval of (705 706) simular to the period size because snd_pcm_rate_hw_refine_cchange() calls snd_interval_floor() for the buffer size. Therefore this value will be interpreted as an integer interval instead of a real interval further on.
This issue seems to exist since the change of 9bb985c38 ("pcm: snd_interval_refine_first/last: exclude value only if also excluded before")
Signed-off-by: Timo Wischer twischer@de.adit-jv.com
On 10/18/18 12:57, Takashi Iwai wrote: This change looks risky. The snd_interval_value() might be called even if the interval isn't reduced to a single value. Rather check openmin instead.
If I would do "if (i->openmin)" on an interval of (x x+1) x+1 would be returned. But this would result in the second issue which I have tried to describe in the commit message: x has to be returned otherwise it is not guaranteed that buffer_size >= 2x period_size. And this would result in continuously Xruns. Therefore I would like to prefer "if (i->openmin && !i->openmax)"
Hm, I overlooked that there is an assert() before that. So a single-value interval is a must at this execution, so it doesn't matter which one to take.
Didn't the assert() hit in your case with x+1, then?
No. For the implementation of
snd_interval_value() (x x+1) is also a valid interval which has only a single value. This is also required because the ALSA neogation rules often end up with intervals like (x x+1) e.g. in case of rounding issues 32ms * 22,05 kHz = 705,6 frames -> (705 706) Therefore assert(snd_interval_single(i)) has to not fail in case of (705 706).
And this is a problematic case no matter which value to take. Your change might "fix" your specific case, but it might break others. No matter which value (min or max) to take, it's basically invalid.
If your fix is logically correct, it's fine. But, judging from the description, it looks like nothing but heuristic based on your specific use cases.
IOW, if we have a good set of unit tests to cover most of possible use cases and this is proven to improve all these, I'll happily take it. But unfortunately there is no good test coverage, so far.
thanks,
Takashi
Best regards Timo
Takashi
diff --git a/src/pcm/interval_inline.h b/src/pcm/interval_inline.h index a68e292..d9a30b2 100644 --- a/src/pcm/interval_inline.h +++ b/src/pcm/interval_inline.h @@ -51,12 +51,14 @@ INTERVAL_INLINE int snd_interval_single(const snd_interval_t *i) { assert(!snd_interval_empty(i)); return (i->min == i->max ||
(i->min + 1 == i->max && i->openmax));
(i->min + 1 == i->max && (i->openmin || i->openmax)));- if (i->openmin && !i->openmax)
return i->max;2.7.4