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

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Date:	Sun, 14 Aug 2016 17:09:58 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Dave Watson <davejwatson@...com>
Cc:	Andrew Morton <akpm@...ux-foundation.org>,
	Russell King <linux@....linux.org.uk>,
	Thomas Gleixner <tglx@...utronix.de>,
	Ingo Molnar <mingo@...hat.com>,
	"H. Peter Anvin" <hpa@...or.com>,
	linux-kernel <linux-kernel@...r.kernel.org>,
	linux-api <linux-api@...r.kernel.org>,
	Paul Turner <pjt@...gle.com>, Andrew Hunter <ahh@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Andy Lutomirski <luto@...capital.net>,
	Andi Kleen <andi@...stfloor.org>, Chris Lameter <cl@...ux.com>,
	Ben Maurer <bmaurer@...com>, rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Catalin Marinas <catalin.marinas@....com>,
	Will Deacon <will.deacon@....com>,
	Michael Kerrisk <mtk.manpages@...il.com>,
	Boqun Feng <boqun.feng@...il.com>
Subject: Re: [RFC PATCH v7 7/7] Restartable sequences: self-tests

----- On Aug 12, 2016, at 4:05 PM, Dave Watson davejwatson@...com 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