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

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Date:	Fri, 12 Aug 2016 19:36:13 +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 11, 2016, at 7:26 PM, Mathieu Desnoyers mathieu.desnoyers@...icios.com wrote:

> ----- On Jul 24, 2016, at 2:01 PM, Dave Watson davejwatson@...com wrote:
> 
>>>> +static inline __attribute__((always_inline))
>>>> +bool rseq_finish(struct rseq_lock *rlock,
>>>> + intptr_t *p, intptr_t to_write,
>>>> + struct rseq_state start_value)
>> 
>>>> This ABI looks like it will work fine for our use case. I don't think it
>>>> has been mentioned yet, but we may still need multiple asm blocks
>>>> for differing numbers of writes. For example, an array-based freelist push:
>> 
>>>> void push(void *obj) {
>>>> if (index < maxlen) {
>>>> freelist[index++] = obj;
>>>> }
>>>> }
>> 
>>>> would be more efficiently implemented with a two-write rseq_finish:
>> 
>>>> rseq_finish2(&freelist[index], obj, // first write
>>>> &index, index + 1, // second write
>>>> ...);
>> 
>>> 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!

Thanks,

Mathieu

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

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