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Message-ID: <6599ad830611230053m7182698cu897abe5d19471aff@mail.gmail.com>
Date: Thu, 23 Nov 2006 00:53:51 -0800
From: "Paul Menage" <menage@google.com>
To: "Pavel Emelianov" <xemul@openvz.org>
Subject: Re: [ckrm-tech] [PATCH 4/13] BC: context handling
Cc: "Kirill Korotaev" <dev@sw.ru>, "Andrew Morton" <akpm@osdl.org>,
       ckrm-tech@lists.sourceforge.net,
       "Linux Kernel Mailing List" <linux-kernel@vger.kernel.org>,
       matthltc@us.ibm.com, hch@infradead.org,
       "Alan Cox" <alan@lxorguk.ukuu.org.uk>, oleg@tv-sign.ru,
       devel@openvz.org
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On 11/23/06, Pavel Emelianov <xemul@openvz.org> wrote:
>
> We can do the following:
>
>   if (tsk == current)
>       /* fast way */
>       tsk->exec_bc = bc;
>   else
>       /* slow way */
>       stop_machine_run(...);
>
> What do you think?

How about having two pointers per task:

- exec_bc, which is the one used for charging
- real_bc, which is the task's actual beancounter

at the start of irq, do

current->exec_bc = &init_bc;

at the end of irq, do

current->exec_bc = current->real_bc;

When moving a task to a different bc do:

task->real_bc = new_bc;
atomic_cmpxchg(&task->exec_bc, old_bc, new_bc);

(with appropriate memory barriers). So if the task is in an irq with a
modified exec_bc pointer, we do nothing, otherwise we update exec_bc
to point to the new real_bc.

Paul
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