Re: [RFC PATCH v7 7/7] Restartable sequences: self-tests

[Mathieu Desnoyers <mathieu.desnoyers-vg+e7yoeK/dWk0Htik3J/w@public.gmane.org>]

----- On Aug 12, 2016, at 4:05 PM, Dave Watson davejwatson-b10kYP2dOMg@public.gmane.org wrote:

>>>>> Would pairing one rseq_start with two rseq_finish do the trick
>>>>> there ?
>>>>
>>>> Yes, two rseq_finish works, as long as the extra rseq management overhead
>>>> is not substantial.
>>>
>>> I've added a commit implementing rseq_finish2() in my rseq volatile
>>> dev branch. You can fetch it at:
>>>
>>> https://github.com/compudj/linux-percpu-dev/tree/rseq-fallback
>>>
>>> I also have a separate test and benchmark tree in addition to the
>>> kernel selftests here:
>>>
>>> https://github.com/compudj/rseq-test
>>>
>>> I named the first write a "speculative" write, and the second write
>>> the "final" write.
>>>
>>> Would you like to extend the test cases to cover your intended use-case ?
>>>
>>
>>Hi Dave!
>>
>>I just pushed a rseq_finish2() test in my rseq-fallback branch. It implements
>>a per-cpu buffer holding pointers, and pushes/pops items to/from it.
>>
>>To use it:
>>
>>cd tools/testing/selftests/rseq
>>./param_test -T b
>>
>>(see -h for advanced usage)
>>
>>Let me know if I got it right!
> 

FYI, I have started implementing rseq_finish_memcpy() and rseq_finish_memcpy_release().
The idea is to perform an inline memcpy as speculative writes before the
final store (offset). I have pushed the work in progress in my dev branch.

This would be an alternative to rseq_finish2() (which I still consider very useful)
in cases where we want to push a sequence of bytes into a ring buffer before updating
the offset counter, without having to rely on memory allocation.

Feedback is welcome!

Thanks,

Mathieu


-- 
Mathieu Desnoyers
EfficiOS Inc.
http://www.efficios.com