linux-kernel - [PATCH] xtensa: add fairness to IRQ handling

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Date:   Fri,  9 Jul 2021 05:05:42 -0700
From:   Max Filippov <jcmvbkbc@...il.com>
To:     linux-xtensa@...ux-xtensa.org
Cc:     Chris Zankel <chris@...kel.net>, linux-kernel@...r.kernel.org,
        Max Filippov <jcmvbkbc@...il.com>
Subject: [PATCH] xtensa: add fairness to IRQ handling

Track which IRQs have been served at each level to make sure that no IRQ
is served more than once while other IRQs at the same level are pending.

Signed-off-by: Max Filippov <jcmvbkbc@...il.com>
---
 arch/xtensa/kernel/traps.c | 7 +++++++
 1 file changed, 7 insertions(+)

diff --git a/arch/xtensa/kernel/traps.c b/arch/xtensa/kernel/traps.c
index efc3a29cde80..874b6efc6fb3 100644
--- a/arch/xtensa/kernel/traps.c
+++ b/arch/xtensa/kernel/traps.c
@@ -268,6 +268,7 @@ void do_interrupt(struct pt_regs *regs)
 		XCHAL_INTLEVEL7_MASK,
 	};
 	struct pt_regs *old_regs;
+	unsigned unhandled = ~0u;
 
 	trace_hardirqs_off();
 
@@ -283,6 +284,10 @@ void do_interrupt(struct pt_regs *regs)
 		for (level = LOCKLEVEL; level > 0; --level) {
 			if (int_at_level & int_level_mask[level]) {
 				int_at_level &= int_level_mask[level];
+				if (int_at_level & unhandled)
+					int_at_level &= unhandled;
+				else
+					unhandled |= int_level_mask[level];
 				break;
 			}
 		}
@@ -290,6 +295,8 @@ void do_interrupt(struct pt_regs *regs)
 		if (level == 0)
 			break;
 
+		/* clear lowest pending irq in the unhandled mask */
+		unhandled ^= (int_at_level & -int_at_level);
 		do_IRQ(__ffs(int_at_level), regs);
 	}
 
-- 
2.20.1