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51 lines
2.1 KiB
Diff
51 lines
2.1 KiB
Diff
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From e804bd1843236a63815e9acfb1a38ebf9a28ef5b Mon Sep 17 00:00:00 2001
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From: Phil Elwell <phil@raspberrypi.com>
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Date: Thu, 31 Aug 2023 16:45:44 +0100
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Subject: [PATCH] drivers: irqchip: irq-bcm2835: Concurrency fix
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The commit shown in Fixes: aims to improve interrupt throughput by
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getting the handlers invoked on different CPU cores. It does so (*) by
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using an irq_ack hook to change the interrupt routing.
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Unfortunately, the IRQ status bits must be cleared at source, which only
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happens once the interrupt handler has run - there is no easy way for
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one core to claim one of the IRQs before sending the remainder to the
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next core on the list, so waking another core immediately results in a
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race with a chance of both cores handling the same IRQ. It is probably
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for this reason that the routing change is deferred to irq_ack, but that
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doesn't guarantee no clashes - after irq_ack is called, control returns
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to bcm2836_chained_handler_irq which proceeds to check for other pending
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IRQs at a time when the next core is probably doing the same thing.
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Since the whole point of the original commit is to distribute the IRQ
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handling, there is no reason to attempt to handle multiple IRQs in one
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interrupt callback, so the problem can be solved (or at least made much
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harder to reproduce) by changing a "while" into an "if", so that each
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invocation only handles one IRQ.
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(*) I'm not convinced it's as effective as claimed since irq_ack is
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called _after_ the interrupt handler, but the author thought it made a
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difference.
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See: https://github.com/raspberrypi/linux/issues/5214
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https://github.com/raspberrypi/linux/pull/1794
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Fixes: fd4c9785bde8 ("ARM64: Round-Robin dispatch IRQs between CPUs.")
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Signed-off-by: Phil Elwell <phil@raspberrypi.com>
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---
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drivers/irqchip/irq-bcm2835.c | 3 ++-
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1 file changed, 2 insertions(+), 1 deletion(-)
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--- a/drivers/irqchip/irq-bcm2835.c
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+++ b/drivers/irqchip/irq-bcm2835.c
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@@ -343,7 +343,8 @@ static void bcm2836_chained_handle_irq(s
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{
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u32 hwirq;
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- while ((hwirq = get_next_armctrl_hwirq()) != ~0)
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+ hwirq = get_next_armctrl_hwirq();
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+ if (hwirq != ~0)
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generic_handle_domain_irq(intc.domain, hwirq);
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}
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