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    SubjectRe: scheduler: IRQs disabled over context switches
    Ingo Molnar wrote:
    > * Davide Libenzi <davidel@xmailserver.org> wrote:
    >
    >
    >>We used to do it in 2.4. What changed to make it fragile? The
    >>threading (TLS) thing?
    >
    >
    > it _should_ work, but in the past we only had trouble from such changes
    > (at least in the O(1) tree of scheduling - 2.4 scheduler is OK.). We
    > could try the patch below. It certainly boots on SMP x86. But it causes
    > a 3.5% slowdown in lat_ctx so i'd not do it unless there are some really
    > good reasons.
    >
    > Ingo
    >
    > --- linux/kernel/sched.c.orig
    > +++ linux/kernel/sched.c
    > @@ -247,9 +247,15 @@ static DEFINE_PER_CPU(struct runqueue, r
    > * Default context-switch locking:
    > */
    > #ifndef prepare_arch_switch
    > -# define prepare_arch_switch(rq, next) do { } while (0)
    > -# define finish_arch_switch(rq, next) spin_unlock_irq(&(rq)->lock)
    > -# define task_running(rq, p) ((rq)->curr == (p))
    > +# define prepare_arch_switch(rq, next) \
    > + do { \
    > + spin_lock(&(next)->switch_lock); \
    > + spin_unlock(&(rq)->lock); \

    spin_unlock_irq?
    -
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