lkml.org 
[lkml]   [2004]   [May]   [23]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
Subjectscheduler: IRQs disabled over context switches
Hi,

The 2.6.6 scheduler disables IRQs across context switches, which is
bad news for IRQ latency on ARM - to the point where 16550A FIFO
UARTs to overrun.

I'm considering defining prepare_arch_switch & co as follows on ARM,
so that we release IRQs over the call to context_switch().

#define prepare_arch_switch(rq,next) \
do { \
spin_lock(&(next)->switch_lock); \
spin_unlock_irq(&(rq)->lock); \
} while (0)
#define finish_arch_switch(rq,prev) \
spin_unlock(&(prev)->switch_lock)
#define task_running(rq,p) \
((rq)->curr == (p) || spin_is_locked(&(p)->switch_lock))
The question is... why are we keeping IRQs disabled over context_switch()
in the first case? Looking at the code, the only thing which is touched
outside of the two tasks is rq->prev_mm. Since runqueues are CPU-
specific and we're holding at least one spinlock, I think the above
is preempt safe and SMP safe.

However, I'd like to find out from someone who knows this code why
IRQs are disabled by default here.

--
Russell King
Linux kernel 2.6 ARM Linux - http://www.arm.linux.org.uk/
maintainer of: 2.6 PCMCIA - http://pcmcia.arm.linux.org.uk/
2.6 Serial core
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2005-03-22 14:03    [from the cache]
©2003-2011 Jasper Spaans