On Friday 29 August 2014 04:33:43 Simon Wise did opine
And Gene did reply:
On 29/08/14 15:40, Len Ovens wrote:
I don't know that the physical technology
matters so much as the OS
being hyperthreading aware and treating each pair of cores like one.
That is making sure that core 0 does not do anything that takes too
long for core 1 to meet it's dead line. I do not know if new Linux
kernels do this, older ones did not. They logged that the chip had
hyperthreading, but still seemed to treat two threads as two
different cores.
Certainly, common wisdom has not kept up with tech changes. I would
be nice to know more.
Not quite on topic, since this isn't to do with Hyper-threading, but
certainly the Linux scheduler has been getting much more sophisticated
in dealing with different kinds of cores ... in ARM it now schedules
tasks for chips with some smaller cores and some faster ones, keeping
them busy with suitable sized tasks.
The ARM kernels running the most recent Samsung tablets (with 4 big
plus 4 little cores) have this GTS in the 3.14 kernels ... it runs all
8 cores together assigning tasks appropriate to each, rather than just
switching between big or little of each pair to save power. Selling
hardware on that scale certainly brings a budget, and since the kernel
is GPL it can't be kept in-house.
Seems that 3.14 has also added a deadline-based scheduler that is
closer to what audio needs from realtime than the extremely low
latency preemption based on priorities that the two older realtime
schedulers offer.
http://www.linuxfoundation.org/news-media/blogs/browse/2014/01/deadline
-scheduling-314
Simon
This message is timely as I haven't tried the deadline scheduler in
several years, so I just switched the config to make it the default, and
its building now. Perhaps it will actually improve both the USB lags, and
the network video playback I get here.
Thank you for an informative post.
Cheers, Gene Heskett
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