linux-kernel - Re: [RFC PATCH] thread_local_abi system call: caching current CPU number (x86)

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Date:	Fri, 17 Jul 2015 16:12:47 +0000 (UTC)
From:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
To:	Ben Maurer <bmaurer@...com>
Cc:	Paul Turner <pjt@...gle.com>, linux-kernel@...r.kernel.org,
	Andrew Hunter <ahh@...gle.com>,
	Peter Zijlstra <peterz@...radead.org>,
	Ingo Molnar <mingo@...hat.com>, rostedt <rostedt@...dmis.org>,
	"Paul E. McKenney" <paulmck@...ux.vnet.ibm.com>,
	Josh Triplett <josh@...htriplett.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Andrew Morton <akpm@...ux-foundation.org>,
	linux-api <linux-api@...r.kernel.org>
Subject: Re: [RFC PATCH] thread_local_abi system call: caching current CPU
 number (x86)

----- On Jul 17, 2015, at 6:49 AM, Ben Maurer bmaurer@...com wrote:

> Mathieu Desnoyers wrote:
>> Expose a new system call allowing threads to register a userspace memory
>> area where to store the current CPU number. Scheduler migration sets the
> 
> I really like that this approach makes it easier to add a per-thread interaction
> between userspace and the kernel in the future.
> 
>>+       if (!tlap || t->thread_local_abi_len <
>>+                       offsetof(struct thread_local_abi, cpu)
>>+                       + sizeof(tlap->cpu))
> 
> Could you save a branch here by enforcing that thread_local_abi_len = 0 if
> thread_local_abi = null?

Yes, good idea! Will do.

Thanks!

Mathieu

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