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Re: [ckrm-tech] [PATCH 4/13] BC: context handling [message #8529 is a reply to message #8528]

Thu, 23 November 2006 09:20

Pavel Emelianov
Messages: 1149
Registered: September 2006

Senior Member

Paul Menage wrote:
> 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);

You mean moving is like this:

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

? Then this won't work:

Initialisation:
current->exec_bc = init_bc;
current->real_bc = init_bc;
...
IRQ:
current->exec_bc = init_bc;
...
old_bc = tsk->real_bc; /* init_bc */
tsk->real_bc = bc1;
cx(tsk->exec_bc, init_bc, bc1); /* ok */
...
Here at the middle of an interrupt
we have bc1 set as exec_bc on task
which IS wrong!
...
current->exec_bc =
current->real_bc;

We need some way to be sure that task isn't running at
the moment we change it's beancounter. Otherwise we're
risking that we'll spoil some temporary context.

> (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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[Message index]

		BC: resource beancounters (v6) (with userpages reclamation + configfs) By: dev on Thu, 09 November 2006 16:42
		[PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper By: dev on Thu, 09 November 2006 16:47
		Re: [PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper By: Cedric Le Goater on Fri, 10 November 2006 15:19
		Re: [PATCH 1/13] BC: atomic_dec_and_lock_irqsave() helper By: dev on Fri, 10 November 2006 16:40
		[PATCH 2/13] BC: Kconfig and Makefile By: dev on Thu, 09 November 2006 16:47
		[PATCH 3/13] BC: beancounters core and API By: dev on Thu, 09 November 2006 16:49
		[PATCH 4/13] BC: context handling By: dev on Thu, 09 November 2006 16:51
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Thu, 23 November 2006 07:48
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Thu, 23 November 2006 08:35
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Thu, 23 November 2006 08:53
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Thu, 23 November 2006 09:20
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Thu, 23 November 2006 09:31
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Thu, 23 November 2006 09:56
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Thu, 23 November 2006 10:18
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Thu, 23 November 2006 10:45
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Fri, 24 November 2006 10:10
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Paul Menage on Sat, 25 November 2006 00:09
		Re: [ckrm-tech] [PATCH 4/13] BC: context handling By: Pavel Emelianov on Mon, 27 November 2006 08:27
		[PATCH 5/13] BC: configfs interface By: dev on Thu, 09 November 2006 16:52
		[PATCH 6/13] BC: kmemsize accounting (core) By: dev on Thu, 09 November 2006 16:53
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Paul Jackson on Thu, 09 November 2006 19:05
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Pekka Enberg on Fri, 10 November 2006 22:50
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Pekka Enberg on Fri, 10 November 2006 22:46
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Pavel Emelianov on Mon, 13 November 2006 12:13
		Re: [PATCH 6/13] BC: kmemsize accounting (core) By: Pavel Machek on Sat, 11 November 2006 05:50
		[PATCH 7/13] BC: kmemsize accounting (hooks) By: dev on Thu, 09 November 2006 16:54
		[PATCH 8/13] BC: privvmpages accounting (core) By: dev on Thu, 09 November 2006 16:56
		[PATCH 9/13] BC: privvmpages accounting (hooks) By: dev on Thu, 09 November 2006 16:57
		[PATCH 10/13] BC: physpages accounting (core) By: dev on Thu, 09 November 2006 16:59
		[PATCH 11/13] BC: physpages accounting (hooks) By: dev on Thu, 09 November 2006 17:01
		[PATCH 12/13] BC: numtasks accounting By: dev on Thu, 09 November 2006 17:02
		[PATCH 13/13] BC: numfiles accounting By: dev on Thu, 09 November 2006 17:03
		Re: BC: resource beancounters (v6) (with userpages reclamation + configfs) By: Herbert Poetzl on Sun, 19 November 2006 19:41

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