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

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Message-ID: <CO1PR15MB09825505EBF36E0C56AA037ADD0C0@CO1PR15MB0982.namprd15.prod.outlook.com>
Date:	Sun, 24 Jul 2016 18:01:08 +0000
From:	Dave Watson <davejwatson@...com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.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@...r.kernel.org" <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

>> +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.