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[SOLVED] Need help disabling software audio mixer (DMIX) #439

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vanfanel opened this issue Nov 19, 2013 · 6 comments
Closed

[SOLVED] Need help disabling software audio mixer (DMIX) #439

vanfanel opened this issue Nov 19, 2013 · 6 comments

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@vanfanel
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Hello there,

I'd like to disable software audio mixer since I'm building a dedicated MIDI synthesizer using the Pi and I need as much raw CPU power as I can get without much overclocking, so rate conversion must be disabled. Only native rates are needed and used.

What I know so far:

-This is what my .asoundrc (or /etc/asound.conf) looks like right now:

pcm.!default {
   type hw
   card 0
}

ctl.!default {
        type hw
        card 0
}

if I understand it correctly, dmix shouldn't be activated because, in my .asoundrc, I am redefining the default plugin with "pcm.!default", and I'm setting it to the first hw, first physical card.
Same for the default control with "ctl.!default". DMIX should NOT be used anymore.

However, there's software mixing: I can do

aplay -D default clip.wav

in two different shells and they will play simultaneusly.
That should not be happening at all if dmix was disabled.
Any program using alsa that uses the "default" plugin shouldn't be using dmix now, and I know specifying it here is indeed unneeded.

Even worse, I can also do

aplay -D hw:0,0 clip.wav

in two different shells and still they play simultaneously. How can that be?? I'm bypassing any plugins by specifying the hw plug, first card, first device. What's going on?!

Mangling with the config files in /usr/share/alsa isn't a good idea since these are used to define default aliases for plugins and devices, and there's no need for that.

So, how can I effectively disable dmix (or whatever software mixing is being used) on Raspbian?
I've been reading and trying to understand http://www.alsa-project.org/main/index.php/Asoundrc to no avail.

@popcornmix
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Are you using snd-bcm2835? (and so headphone or HDMI output?)
That supports 8 substreams, so you can open multiple streams and the mixing is done effectively in hardware (on the GPU).

@vanfanel
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Author

Yes, I'm using snd-bcm2835. I didn't know the Raspberry Pi onboard audio core had hardware mixing! Impressive..
Does it also support 22KHz sample rates natively? I seem to be able to play these even with the mentioned .asoundrc configuration...

If it does, how could I verify DMIX is disabled?

I neved had a GNU/Linux system with hardware mixing hardware before, so using the aforementioned configuration always worked for me and I could easily tell when DMIX was disabled (ie, bypassed by redefining the default plugin as I have done).

@popcornmix
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Yes, GPU supports resampling so I any sampling rates from 8kHz to 48kHz are supported natively.
I believe from your asound.conf that DMIX will be disabled.

If you really want to be sure, then you could rebuild kernel with 1 substream and only 48kHz supported and confirm that it breaks (but I'm pretty sure it will with that asound.conf).

@vanfanel
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Last question regarding this: is resampling and mixing done in hardware or is it a software kernel feature? What I really mean is: will I reduce CPU usage during a single, native-rate playback if I recompile the kernel and disable streams and different rates? (Supposing there's such thing as a "native sample rate")

@popcornmix
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The resampling and mixing is being done on the GPU. There should be no observable CPU usage due to this on ARM.
As far as the ARM is concerned there is no native sampling rate. The ALSA driver reports it supports a continuous range from 8kHz to 48kHz.

@vanfanel
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Thanks for your concise and clear responses, popcornmix! Now I think I understand all I wanted about this :)

popcornmix pushed a commit that referenced this issue Aug 28, 2019
…s_blob()

Calling ceph_buffer_put() in __ceph_build_xattrs_blob() may result in
freeing the i_xattrs.blob buffer while holding the i_ceph_lock.  This can
be fixed by having this function returning the old blob buffer and have
the callers of this function freeing it when the lock is released.

The following backtrace was triggered by fstests generic/117.

  BUG: sleeping function called from invalid context at mm/vmalloc.c:2283
  in_atomic(): 1, irqs_disabled(): 0, pid: 649, name: fsstress
  4 locks held by fsstress/649:
   #0: 00000000a7478e7e (&type->s_umount_key#19){++++}, at: iterate_supers+0x77/0xf0
   #1: 00000000f8de1423 (&(&ci->i_ceph_lock)->rlock){+.+.}, at: ceph_check_caps+0x7b/0xc60
   #2: 00000000562f2b27 (&s->s_mutex){+.+.}, at: ceph_check_caps+0x3bd/0xc60
   #3: 00000000f83ce16a (&mdsc->snap_rwsem){++++}, at: ceph_check_caps+0x3ed/0xc60
  CPU: 1 PID: 649 Comm: fsstress Not tainted 5.2.0+ #439
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-prebuilt.qemu.org 04/01/2014
  Call Trace:
   dump_stack+0x67/0x90
   ___might_sleep.cold+0x9f/0xb1
   vfree+0x4b/0x60
   ceph_buffer_release+0x1b/0x60
   __ceph_build_xattrs_blob+0x12b/0x170
   __send_cap+0x302/0x540
   ? __lock_acquire+0x23c/0x1e40
   ? __mark_caps_flushing+0x15c/0x280
   ? _raw_spin_unlock+0x24/0x30
   ceph_check_caps+0x5f0/0xc60
   ceph_flush_dirty_caps+0x7c/0x150
   ? __ia32_sys_fdatasync+0x20/0x20
   ceph_sync_fs+0x5a/0x130
   iterate_supers+0x8f/0xf0
   ksys_sync+0x4f/0xb0
   __ia32_sys_sync+0xa/0x10
   do_syscall_64+0x50/0x1c0
   entry_SYSCALL_64_after_hwframe+0x49/0xbe
  RIP: 0033:0x7fc6409ab617

Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
popcornmix pushed a commit that referenced this issue Sep 17, 2019
…s_blob()

[ Upstream commit 12fe3dd ]

Calling ceph_buffer_put() in __ceph_build_xattrs_blob() may result in
freeing the i_xattrs.blob buffer while holding the i_ceph_lock.  This can
be fixed by having this function returning the old blob buffer and have
the callers of this function freeing it when the lock is released.

The following backtrace was triggered by fstests generic/117.

  BUG: sleeping function called from invalid context at mm/vmalloc.c:2283
  in_atomic(): 1, irqs_disabled(): 0, pid: 649, name: fsstress
  4 locks held by fsstress/649:
   #0: 00000000a7478e7e (&type->s_umount_key#19){++++}, at: iterate_supers+0x77/0xf0
   #1: 00000000f8de1423 (&(&ci->i_ceph_lock)->rlock){+.+.}, at: ceph_check_caps+0x7b/0xc60
   #2: 00000000562f2b27 (&s->s_mutex){+.+.}, at: ceph_check_caps+0x3bd/0xc60
   #3: 00000000f83ce16a (&mdsc->snap_rwsem){++++}, at: ceph_check_caps+0x3ed/0xc60
  CPU: 1 PID: 649 Comm: fsstress Not tainted 5.2.0+ #439
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-prebuilt.qemu.org 04/01/2014
  Call Trace:
   dump_stack+0x67/0x90
   ___might_sleep.cold+0x9f/0xb1
   vfree+0x4b/0x60
   ceph_buffer_release+0x1b/0x60
   __ceph_build_xattrs_blob+0x12b/0x170
   __send_cap+0x302/0x540
   ? __lock_acquire+0x23c/0x1e40
   ? __mark_caps_flushing+0x15c/0x280
   ? _raw_spin_unlock+0x24/0x30
   ceph_check_caps+0x5f0/0xc60
   ceph_flush_dirty_caps+0x7c/0x150
   ? __ia32_sys_fdatasync+0x20/0x20
   ceph_sync_fs+0x5a/0x130
   iterate_supers+0x8f/0xf0
   ksys_sync+0x4f/0xb0
   __ia32_sys_sync+0xa/0x10
   do_syscall_64+0x50/0x1c0
   entry_SYSCALL_64_after_hwframe+0x49/0xbe
  RIP: 0033:0x7fc6409ab617

Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
popcornmix pushed a commit that referenced this issue Sep 17, 2019
…s_blob()

[ Upstream commit 12fe3dd ]

Calling ceph_buffer_put() in __ceph_build_xattrs_blob() may result in
freeing the i_xattrs.blob buffer while holding the i_ceph_lock.  This can
be fixed by having this function returning the old blob buffer and have
the callers of this function freeing it when the lock is released.

The following backtrace was triggered by fstests generic/117.

  BUG: sleeping function called from invalid context at mm/vmalloc.c:2283
  in_atomic(): 1, irqs_disabled(): 0, pid: 649, name: fsstress
  4 locks held by fsstress/649:
   #0: 00000000a7478e7e (&type->s_umount_key#19){++++}, at: iterate_supers+0x77/0xf0
   #1: 00000000f8de1423 (&(&ci->i_ceph_lock)->rlock){+.+.}, at: ceph_check_caps+0x7b/0xc60
   #2: 00000000562f2b27 (&s->s_mutex){+.+.}, at: ceph_check_caps+0x3bd/0xc60
   #3: 00000000f83ce16a (&mdsc->snap_rwsem){++++}, at: ceph_check_caps+0x3ed/0xc60
  CPU: 1 PID: 649 Comm: fsstress Not tainted 5.2.0+ #439
  Hardware name: QEMU Standard PC (i440FX + PIIX, 1996), BIOS rel-1.12.1-0-ga5cab58-prebuilt.qemu.org 04/01/2014
  Call Trace:
   dump_stack+0x67/0x90
   ___might_sleep.cold+0x9f/0xb1
   vfree+0x4b/0x60
   ceph_buffer_release+0x1b/0x60
   __ceph_build_xattrs_blob+0x12b/0x170
   __send_cap+0x302/0x540
   ? __lock_acquire+0x23c/0x1e40
   ? __mark_caps_flushing+0x15c/0x280
   ? _raw_spin_unlock+0x24/0x30
   ceph_check_caps+0x5f0/0xc60
   ceph_flush_dirty_caps+0x7c/0x150
   ? __ia32_sys_fdatasync+0x20/0x20
   ceph_sync_fs+0x5a/0x130
   iterate_supers+0x8f/0xf0
   ksys_sync+0x4f/0xb0
   __ia32_sys_sync+0xa/0x10
   do_syscall_64+0x50/0x1c0
   entry_SYSCALL_64_after_hwframe+0x49/0xbe
  RIP: 0033:0x7fc6409ab617

Signed-off-by: Luis Henriques <lhenriques@suse.com>
Reviewed-by: Jeff Layton <jlayton@kernel.org>
Signed-off-by: Ilya Dryomov <idryomov@gmail.com>
Signed-off-by: Sasha Levin <sashal@kernel.org>
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