[Xen-devel] [PATCH] gic: drop interrupts enabling on interrupts processing

[Andrii Anisov <andrii.anisov@xxxxxxxxx>]

From: Andrii Anisov <andrii_anisov@xxxxxxxx>

This reduces the number of context switches in case we have coming guest
interrupts from different sources at a high rate. What is likely for
multimedia use-cases.
Having irqs unlocked here makes us go through trap path again in case we
have a new guest interrupt arrived (even with the same priority, after
`desc->handler->end(desc)` in `do_IRQ()`), what is just a processor
cycles wasting. We will catch them all in the `gic_interrupt() function
loop anyway. And the guest irqs arrival prioritization is meaningless
here, it is only effective at guest's level.

Signed-off-by: Andrii Anisov <andrii_anisov@xxxxxxxx>

---

This is the patch [1] from RFC series, with extended commit message.

[1] https://lists.xenproject.org/archives/html/xen-devel/2018-11/msg03286.html

---
 xen/arch/arm/gic.c | 2 --
 1 file changed, 2 deletions(-)

diff --git a/xen/arch/arm/gic.c b/xen/arch/arm/gic.c
index 6cc7dec..9f5cd95 100644
--- a/xen/arch/arm/gic.c
+++ b/xen/arch/arm/gic.c
@@ -386,10 +386,8 @@ void gic_interrupt(struct cpu_user_regs *regs, int is_fiq)
 
         if ( likely(irq >= 16 && irq < 1020) )
         {
-            local_irq_enable();
             isb();
             do_IRQ(regs, irq, is_fiq);
-            local_irq_disable();
         }
         else if ( is_lpi(irq) )
         {
-- 
2.7.4


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