On Thu, 24 Jun 2010, npiggin@xxxxxxx wrote:
> +#define DEFINE_LGLOCK(name) \
> + \
> + DEFINE_PER_CPU(arch_spinlock_t, name##_lock); \
Uuurgh. You want to make that an arch_spinlock ? Just to avoid the
preempt_count overflow when you lock all cpu locks nested ?
I'm really not happy about that, it's going to be a complete nightmare
for RT. If you wanted to make this a present for RT giving the
scalability stuff massive testing, then you failed miserably :)
I know how to fix it, but can't we go for an approach which
does not require massive RT patching again ?
struct percpu_lock {
spinlock_t lock;
unsigned global_state;
};
And let the lock function do:
spin_lock(&pcp->lock);
while (pcp->global_state)
cpu_relax();
So the global lock side can take each single lock, modify the percpu
"global state" and release the lock. On unlock you just need to reset
the global state w/o taking the percpu lock and be done.
I doubt that the extra conditional in the lock path is going to be
relevant overhead, compared to the spin_lock it's noise.
Thanks,
tglx
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