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    SubjectRe: [ckrm-tech] [PATCH 4/13] BC: context handling
    Paul Menage wrote:
    > On 11/23/06, Pavel Emelianov <xemul@openvz.org> wrote:
    >> 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!
    >
    > You could get round that by having a separate "irq_bc" that's never
    > valid for a task not in an interrupt.

    No no no. This is not what is needed. You see, we do have to
    set exec_bc as temporary (and atomic) context. Having temporary
    context is 1. flexible 2. needed by beancounters' network accountig.
    We have to track this particular scenario.

    Moreover making get_exec_bc() as
    if (in_interrupt())
    return &irq_bc;
    else
    return current->exec_bc;
    is awful. It must me simple and stupid to allow us making temporary
    contexts in any place of code.

    Maybe we can make smth similar to wait_task_inactive and change
    it's beancounter before unlocking the runqueue?

    > Paul
    >
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