If irq_exit() is called on the arch's specified irq stack, it should be safe to run softirqs inline under that same irq stack as it is near empty by the time we call irq_exit().
Hardirqs can nest but irq exit's processing of softirqs only happen in the inner most hardirq. So if we use the same stack for both the worst case scenario is: hardirq -> softirq -> hardirq. But then the first hardirq can be ignored as its stack is mostly empty. So the stack merge in this case looks acceptable. So lets adapt the irq exit's softirq stack on top of a new arch symbol that can be defined when irq_exit() runs on the irq stack. That way we can spare some stack switch on irq processing and all the cache issues that come along. Signed-off-by: Frederic Weisbecker <[email protected]> Cc: Benjamin Herrenschmidt <[email protected]> Cc: Paul Mackerras <[email protected]> Cc: Ingo Molnar <[email protected]> Cc: Thomas Gleixner <[email protected]> Cc: Peter Zijlstra <[email protected]> Cc: H. Peter Anvin <[email protected]> Cc: Linus Torvalds <[email protected]> Cc: Paul Mackerras <[email protected]> Cc: James Hogan <[email protected]> Cc: James E.J. Bottomley <[email protected]> Cc: Helge Deller <[email protected]> Cc: Martin Schwidefsky <[email protected]> Cc: Heiko Carstens <[email protected]> Cc: David S. Miller <[email protected]> Cc: Andrew Morton <[email protected]> --- kernel/softirq.c | 14 ++++++++++---- 1 file changed, 10 insertions(+), 4 deletions(-) diff --git a/kernel/softirq.c b/kernel/softirq.c index 2b4328e..317778c 100644 --- a/kernel/softirq.c +++ b/kernel/softirq.c @@ -332,15 +332,21 @@ void irq_enter(void) static inline void invoke_softirq(void) { if (!force_irqthreads) { +#ifdef __ARCH_IRQ_EXIT_ON_IRQ_STACK /* * We can safely execute softirq on the current stack if * it is the irq stack, because it should be near empty - * at this stage. But we have no way to know if the arch - * calls irq_exit() on the irq stack. So call softirq - * in its own stack to prevent from any overrun on top - * of a potentially deep task stack. + * at this stage. + */ + __do_softirq(); +#else + /* + * Otherwise, irq_exit() is called on the task stack that can + * be potentially deep already. So call softirq in its own stack + * to prevent from any overrun. */ do_softirq_own_stack(); +#endif } else { wakeup_softirqd(); } -- 1.8.3.1 -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [email protected] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
