x86: Tell about irq stack coverage

x86-64 runs irq_exit() under the irq stack. So it can afford
to run softirqs in hardirq exit without the need to switch
the stacks. The hardirq stack is good enough for that.

Now x86-64 runs softirqs in the hardirq stack anyway, so what we
mostly skip is some needless per cpu refcounting updates there.

x86-32 is not concerned because it only runs the irq handler on
the irq stack.

Acked-by: Linus Torvalds <[email protected]>
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]>

diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
index ee2fb9d37745887eb16255cbd30adacbdcc1ecae..99eb1cc30dac96faa37f8d9d5c68e28e649aeee1 100644 (file)
--- a/arch/x86/Kconfig
+++ b/arch/x86/Kconfig
@@ -123,6 +123,7 @@ config X86
        select COMPAT_OLD_SIGACTION if IA32_EMULATION
        select RTC_LIB
        select HAVE_DEBUG_STACKOVERFLOW
+       select HAVE_IRQ_EXIT_ON_IRQ_STACK if X86_64
 
 config INSTRUCTION_DECODER
        def_bool y