linux-kernel - Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory barrier (v5)

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Date:	Tue, 12 Jan 2010 21:00:23 -0800
From:	Nicholas Miell <nmiell@...cast.net>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	linux-kernel@...r.kernel.org,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Steven Rostedt <rostedt@...dmis.org>,
	Oleg Nesterov <oleg@...hat.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...e.hu>, akpm@...ux-foundation.org,
	josh@...htriplett.org, tglx@...utronix.de, Valdis.Kletnieks@...edu,
	dhowells@...hat.com, laijs@...fujitsu.com, dipankar@...ibm.com
Subject: Re: [RFC PATCH] introduce sys_membarrier(): process-wide memory
 barrier (v5)

On Tue, 2010-01-12 at 20:37 -0500, Mathieu Desnoyers wrote:
> + * sys_membarrier - issue memory barrier on current process running threads
> + * @expedited: (0) Lowest overhead. Few milliseconds latency.
> + *             (1) Few microseconds latency.
> + *

Alternate ABI proposal, keeping the possibility of future expansion in
mind:

/*
Mandatory flags to the membarrier system call that the kernel must
understand are in the high 16 bits.
*/
#define MEMBARRIER_MANDATORY_MASK 0xFFFF0000

/*
Optional hints that the kernel can ignore are in the low 16 bits.
*/
#define MEMBARRIER_OPTIONAL_MASK 0x0000FFFF

#define MEMBARRIER_EXPEDITED 1

extern int membarrier(unsigned int flags);

And then add to the system call itself:

if ((flags & MEMBARRIER_MANDATORY_MASK) != 0)
	return -EINVAL;


-- 
Nicholas Miell <nmiell@...cast.net>

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