linux-kernel - Re: [RFC] Thread Migration Preemption

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Date:	Thu, 05 Jul 2007 18:46:46 -0400
From:	Steven Rostedt <rostedt@...dmis.org>
To:	Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>
Cc:	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	Thomas Gleixner <tglx@...utronix.de>
Subject: Re: [RFC] Thread Migration Preemption

On Thu, 2007-07-05 at 17:51 -0400, Mathieu Desnoyers wrote:
> Thread Migration Preemption
> 
> This patch adds the ability to protect critical sections from migration to
> another CPU without disabling preemption.
> 
> This will be useful to minimize the amount of preemption disabling for the -rt
> patch. It will help leveraging improvements brought by the local_t types in
> asm/local.h (see Documentation/local_ops.txt). Note that the updates done to
> variables protected by migration_disable must be either atomic or protected from
> concurrent updates done by other threads.
> 
> Typical use:
> 
> migration_disable();
> local_inc(&__get_cpu_var(&my_local_t_var));
> migration_enable();
> 
> Which will increment the variable atomically wrt the local CPU.
> 
> Comments (such as how to integrate this in the already almost full
> preempt_count) are welcome.

Ingo and Thomas, this also would help with the IRQ thread running a
softirq issue.  We wouldn't need to bind to a CPU the thread. We could
simply disable the ability to migrate while the IRQ thread was handling
the softirqs.

-- Steve


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