Messages in this thread | | | Date | Thu, 23 Nov 2006 17:59:10 +0300 | From | Oleg Nesterov <> | Subject | Re: [patch] cpufreq: mark cpufreq_tsc() as core_initcall_sync |
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(Sorry, responding to the wrong message)
Paul E. McKenney wrote: > > I am concerned about this as well, and am beginning to suspect that I > need to make a special-purpose primitive specifically for Jens that he > can include with his code.
How about this?
struct xxx_struct { int completed; atomic_t ctr[2]; struct mutex mutex; wait_queue_head_t wq; };
void init_xxx_struct(struct xxx_struct *sp) { sp->completed = 0; atomic_set(sp->ctr + 0, 1); // active atomic_set(sp->ctr + 1, 0); // inactive mutex_init(&sp->mutex); init_waitqueue_head(&sp->wq); }
int xxx_read_lock(struct xxx_struct *sp) { for (;;) { int idx = sp->completed & 0x1; if (likely(atomic_inc_not_zero(sp->ctr + idx))) return idx; } }
void xxx_read_unlock(struct xxx_struct *sp, int idx) { if (unlikely(atomic_dec_and_test(sp->ctr + idx))) wake_up(&sp->wq); }
void synchronize_xxx(struct xxx_struct *sp) { int idx;
mutex_lock(&sp->mutex);
idx = ++sp->completed & 0x1; smp_mb__before_atomic_inc(); atomic_inc(&sp->ctr + idx);
idx = !idx; if (!atomic_dec_and_test(&sp->ctr + idx)) __wait_event(&sp->wq, !atomic_read(&sp->ctr + idx));
mutex_unlock(&sp->mutex); }
Yes, cache thrashing... But I think this is hard to avoid if we want writer to be fast.
I do not claim this is the best solution, but for some reason I'd like to suggest something that doesn't need synchronize_sched(). What do you think about correctness at least?
Oleg.
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