[pulseaudio-discuss] Distribution kernels and glitch-free (Packagers, read this!)

Colin Guthrie gmane at colin.guthr.ie
Mon Feb 23 09:42:44 PST 2009

'Twas brillig, and Lennart Poettering at 23/02/09 16:31 did gyre and gimble:
> On Mon, 23.02.09 10:14, Colin Guthrie (gmane at colin.guthr.ie) wrote:
>> 'Twas brillig, and Lennart Poettering at 23/02/09 02:05 did gyre and gimble:
>>> OpenSUSE apparently does not enable it. The same is true for
>>> Ubuntu. Same for Debian. Note sure about Mandriva.
>> Here is a (not quite current) grep from my running kernel (it's .27 as  
>> .28/.29 both break my intel graphics :( at the moment):
>> $ zgrep -E "HZ|PREEMP" /proc/config.gz
>> # CONFIG_PREEMPT_NONE is not set
>> # CONFIG_PREEMPT is not set
>> # CONFIG_HZ_100 is not set
>> # CONFIG_HZ_250 is not set
>> # CONFIG_HZ_300 is not set
>> CONFIG_HZ_1000=y
>> CONFIG_HZ=1000
>> I'll ask our kernel team why PREEMPT is not on as I've no idea of the  
>> consequences. My guess is that it relates to graphics drivers...
> The Fedora kernels set PREEMPT_VOLUNTARY as well as it seems.

Yeah, I asked this of one of our Kernel guys. This is his response, 
which seems pretty sensible and balanced to me :)

Well, Lennart actually answered your question  ;-)

Full Preempt used to break several drivers, including graphic, wireless, ...

And Lennarts suggestion to "get rid of low-quality drivers" is not 
really an option for distributions...
Yeah, we try to avoid them where possible, but a "crappy driver" is 
almost always better than none at all...

Another problem is that there also has been applications crashing if the 
kernel was full Preempt... So it's another no-no for a distribution that 
has to support it's customers...

That's why we chose Voluntary Preempt because it preempts the kernel in 
"safe places" without breaking drivers and applications...

Of course things might have changed atleast for some drivers and 
applications so it should be tested again, but I dont think it's for 
main kernel yet...

Of course this is not my decision to make, but I think kernel team agree 
with me on this....

Anyway, the upcoming kernel-tmb-2.6.29-0.rc6.1mdv will enable full 
Preempt on -desktop(586) flavours to try and see what breaks...


Colin Guthrie

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