Package: src:linux Version: 4.17.0-1 Severity: normal -----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512
Dear kernel maintainers, starting from `linux-image-4.17.0-1-amd64`, the debian kernel comes with `CONFIG_SND_HDA_POWER_SAVE_DEFAULT=1` (it was set to `0` before). I wonder if this change was intended, for two reasons. 1. According to the documentation at [1]: ``CONFIG_SND_HDA_POWER_SAVE_DEFAULT`` Kconfig options. Setting this to 1 (the minimum value) isn't recommended because many applications try to reopen the device frequently. 10 would be a good choice for normal operations. 2. Moreover, grepping through the config shows that this change was only applied to `CONFIG_SND_HDA`, not to `CONFIG_SND_AC97`. $ grep POWER_SAVE_DEFAULT config-4.18.0-3-amd64 CONFIG_SND_AC97_POWER_SAVE_DEFAULT=0 CONFIG_SND_HDA_POWER_SAVE_DEFAULT=1 In any case, this breaks things on my laptop. In short, the function call `snd_pcm_open()` (to open an audio device), which used to take around 1 ms, now takes an average of 40 ms, with maximum peaks measured to 3 seconds. What's unfortunate is that this function might be called from within the GTK+ main loop, synchronously, causing apps like the terminal or a text editor to hang until the call returns. And this function is called A LOT, due to event sounds. I described this a bit more in details on the ALSA mailing list at [2]. The kernel documentation at [1] mentions: Also, it often takes certain time to wake up from the power-down to the active state. These are often hardly to fix, so don't report extra bug reports unless you have a fix patch ;-) Reading that, and after discovering that event sounds are implemented synchronously (well, at least using GNOME/Wayland), I wonder if `CONFIG_SND_HDA_POWER_SAVE_DEFAULT` shouldn't be reverted to 0. Thanks, Arnaud - ---- [1]: https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/sound/designs/powersave.rst [2]: http://mailman.alsa-project.org/pipermail/alsa-devel/2018-December/143167.html -----BEGIN PGP SIGNATURE----- iQJTBAEBCgA9FiEE0Kl7ndbut+9n4bYs5yXoeRRgAhYFAlwqLR8fHGFybmF1ZC5y ZWJpbGxvdXRAY29sbGFib3JhLmNvbQAKCRDnJeh5FGACFuSTD/9dmrbRgG3FfSue 0NPIwSNhV7++OqFZKt9mn3tX9XXrIJnx9SdJLAZ+Tt3R7/uwocdutGUZTT23e2kc BUoeEPflIevoOOE6ZetdLuUotqa3FvmJMfx/odlGu2zehGkwPzjIJJ3mZ8glYTj2 +/aUi6N4GMgesqhstAAeKgz3/pfz6gWr1uf6fy+OjPSzk+xBU2mOUBvh+Rs34tch KHUO2ysZ5RwJ73cnqsJcfv4krnF4Rojl5ooijNc5cldxfBdZsN6mfljOnCOFzkgZ TqG+g0zlY8aGxriDxJwfM1gR9RGXbrVAD++N/KnulSzVK/r4osdtawrnVnbZ38rq zBQ1O+WvXdWGsERj0Hn7PWHxO6eMo9RBYIFAanwbJceIyiJYxm+Zr3xBtVefEA7D e5aWUL0AvZpA2ma1bs3xW1IhaGst8mhACu/ef+qbZBqenUfUdfOQ3SNf7wqJQvEe u1u1O/3JC7qs+By8Kz9hBaIkblZF4IgJ9kCllg9EckTLkg2vU9rR0vyr+2BIidDj LjmkeFcul52bE1K/azGk+Xjj1L8iGPVFiLrzPjgZOJAI7bkFIFSLYAl8Ucw3p4x5 QGq7yAFLbUgcUJ7MyvRFOEYrRjb/xExtdyG7an8U3IS/1P85FdxuHTQTGtWIPUf7 zZx7p3/ABpZzkT2cM+xRJOMoOzwNeg== =aX+w -----END PGP SIGNATURE-----
