hi,

happy new year every one. During the free days I've tried to link BitwigStudio to the webapp [1]cables.gl over virmidi. Unfortunately Bitwig Studio only supports rawmidi. What I discovered is that there is a strange slowness when sending data to virmidi caused by snd_rawmidi_drain().

I've posted two tiny, self-contained c apps to: [2]https://gist.github.com/ensonic/c7588b87fa6c1fa94a8f753b1e0aa394 See some examples below. 2 observations: * snd_rawmidi_type() is *not* reporting virmidi as VIRTUAL * snd_rawmidi_drain() takes about 60ms! on virtual vs. less that 0.1 ms on usb midi (I checked all my hw midi and the worst was avg=1ms on physical midi image unitor8)

When comparing the implementations: [3]https://github.com/alsa-project/alsa-lib/blob/master/ src/rawmidi/rawmidi_virt.c#L173 [4]https://github.com/alsa-project/alsa-lib/blob/master/ src/rawmidi/rawmidi_hw.c#L164 I see that the hw one results in an IOCTL (SNDRV_RAWMIDI_IOCTL_DRAIN) which I can see when strac'ing app and I wonder if this is the root cause? Why is rawmidi_virt.c not used for virmidi? From poking at snd_rawmidi_open_conf() I have not yet figured where this is decided ....

If the IOCTl is the right code path, any idea why it is slow? Is the virmidi driver not reporting buffer fill status or something like that?

Stefan

amidi -l

Dir Device Name IO hw:0,0,0 Scarlett 18i20 USB MIDI 1 IO hw:3,0,0 nanoKEY2 nanoKEY2 _ KEYBOARD IO hw:5,0,0 nanoKONTROL nanoKONTROL _ SLIDE IO hw:10,0 Virtual Raw MIDI (16 subdevices) IO hw:11,0 Virtual Raw MIDI (16 subdevices)

# using direct i/o to virmidi - all good

./rawmidi_oss /dev/midi11 0

Using device '/dev/midi11' without draining write took min= 0.0015 ms, avg= 0.0016 ms, max= 0.0110 ms

./rawmidi_oss /dev/midi11 1

Using device '/dev/midi11' with draining write took min= 0.0015 ms, avg= 0.0017 ms, max= 0.0101 ms drain took min= 0.0001 ms, avg= 0.0001 ms, max= 0.0008 ms

# using snd_rawmidi to virmidi - slow drain operations

./rawmidi_alsa hw:11,0 0

Using device 'hw:11,0' without draining SND_RAWMIDI_TYPE_HW write took min= 0.0010 ms, avg= 0.0011 ms, max= 0.0056 ms

./rawmidi_alsa hw:11,0 1

Using device 'hw:11,0' with draining SND_RAWMIDI_TYPE_HW write took min= 0.0016 ms, avg= 0.0040 ms, max= 0.0077 ms drain took min= 55.9951 ms, avg= 60.4330 ms, max= 64.0653 ms

# using snd_rawmidi to usb hw - all good

./rawmidi_alsa hw:3,0 0

Using device 'hw:3,0' without draining SND_RAWMIDI_TYPE_HW write took min= 0.0012 ms, avg= 0.0015 ms, max= 0.0121 ms

./rawmidi_alsa hw:3,0 1

Using device 'hw:3,0' with draining SND_RAWMIDI_TYPE_HW write took min= 0.0024 ms, avg= 0.0032 ms, max= 0.0110 ms drain took min= 0.0293 ms, avg= 0.0636 ms, max= 0.2277 ms

References

1. http://cables.gl/ 2. https://gist.github.com/ensonic/c7588b87fa6c1fa94a8f753b1e0aa394 3. https://github.com/alsa-project/alsa-lib/blob/master/src/rawmidi/rawmidi_vir... 4. https://github.com/alsa-project/alsa-lib/blob/master/src/rawmidi/rawmidi_hw....