On 20/09/2023 13:30, Anton Ivanov wrote:
On 20/09/2023 12:14, Anton Ivanov wrote:
Added support for kernel side fpu store/restore and real
kernel_fpu_begin/kernel_fpu_end using gcc intrinsics. Enabled PREEMPT.
It boots and seems to be alive and kicking. I do not notice any significant
effect on performance either.
I take my words back - I was testing with VOLUNTARY which seems to provide a
difference withing the margin of error.
Enabling forced preemption drops the time for
find /usr -type f -exec cat {} > /dev/null \;
from
real 19m11.207s
user 0m0.180s
sys 2m41.160s
to
real 3m13.647s
user 0m0.000s
sys 2m58.270s
And boot time from 11.5s to 6s.
It did complain on shutdown though with some traces. Nothing while running.
The complaint I get is from here:
https://elixir.bootlin.com/linux/v6.6-rc2/source/kernel/sched/core.c#L5229
This looks broken for UP. On UP the preempt count is not inc-ed twice, because
the UP version of _raw_spin_lock_irq does not touch it, hence it is odd, not
even.
Other than that it all works. Some decrease in total network throughput
(expected), serious increase in userspace responsiveness (more than expected).
No crashes.
This leaves opened two questions:
1. Do we do anything about this one
2. How do we enable preemption for voluntary.
The patch will hit the mailing list shortly.
How do I test it from here onwards?
The question still stands. Can we use anything as a specific test suite? It is
not an area I am familiar with, so any pointers will be welcome.
I am happy to throw the patches on the list as an RFC, though I would prefer to
test first :)
--
Anton R. Ivanov
https://www.kot-begemot.co.uk/
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