linux-kernel - [PATCH] irq: revert non-working patch to affinity defaults

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Date:	Thu, 02 Apr 2015 17:50:22 -0700
From:	Jesse Brandeburg <jesse.brandeburg@...el.com>
To:	torvalds@...ux-foundation.org
Cc:	Thomas Gleixner <tglx@...utronix.de>, linux-kernel@...r.kernel.org,
	John <jw@...learfallout.net>, Ingo Molnar <mingo@...nel.org>
Subject: [PATCH] irq: revert non-working patch to affinity defaults

I've seen a couple of reports of issues since commit e2e64a932556 ("genirq:
Set initial affinity in irq_set_affinity_hint()") where the
affinity for the interrupt when programmed via
/proc/irq/<nnn>/smp_affinity will not be able to stick.  It changes back
to some previous value at the next interrupt on that IRQ.

The original intent was to fix the broken default behavior of all IRQs
for a device starting up on CPU0.  With a network card with 64 or more
queues, all 64 queue's interrupt vectors end up on CPU0 which can have
bad side effects, and has to be fixed by the irqbalance daemon, or by
the user at every boot with some kind of affinity script.

The symptom is that after a driver calls set_irq_affinity_hint, the
affinity will be set for that interrupt (and readable via /proc/...),
but on the first irq for that vector, the affinity for CPU0 or CPU1
resets to the default.  The rest of the irq affinites seem to work and
everything is fine.

Impact if we don't fix this for 4.0.0:
	Some users won't be able to set irq affinity as expected, on
	some cpus.

I've spent a chunk of time trying to debug this with no luck and suggest
that we revert the change if no-one else can help me debug what is going
wrong, we can pick up the change later.

This commit would also revert commit 4fe7ffb7e17ca ("genirq: Fix null pointer
reference in irq_set_affinity_hint()") which was a bug fix to the original
patch.

Signed-off-by: Jesse Brandeburg <jesse.brandeburg@...el.com>
CC: Ingo Molnar <mingo@...nel.org>
CC: Thomas Gleixner <tglx@...utronix.de>
CC: John <jw@...learfallout.net>
---
 kernel/irq/manage.c |    3 ---
 1 file changed, 3 deletions(-)

diff --git a/kernel/irq/manage.c b/kernel/irq/manage.c
index 886d09e..c166a16 100644
--- a/kernel/irq/manage.c
+++ b/kernel/irq/manage.c
@@ -243,9 +243,6 @@ int irq_set_affinity_hint(unsigned int irq, const struct cpumask *m)
 		return -EINVAL;
 	desc->affinity_hint = m;
 	irq_put_desc_unlock(desc, flags);
-	/* set the initial affinity to prevent every interrupt being on CPU0 */
-	if (m)
-		__irq_set_affinity(irq, m, false);
 	return 0;
 }
 EXPORT_SYMBOL_GPL(irq_set_affinity_hint);

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