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From: Keith Busch <keith.busch@intel.com>
To: Andrei Vagin <avagin@virtuozzo.com>
Cc: linux-kernel@vger.kernel.org,
	Thomas Gleixner <tglx@linutronix.de>,
	Xiaolong Ye <xiaolong.ye@intel.com>
Subject: Re: irq/affinity: Fix extra vecs calculation
Date: Wed, 19 Apr 2017 17:53:09 -0400	[thread overview]
Message-ID: <20170419215308.GF16224@localhost.localdomain> (raw)
In-Reply-To: <20170419195343.GA24395@outlook.office365.com>

On Wed, Apr 19, 2017 at 12:53:44PM -0700, Andrei Vagin wrote:
> On Wed, Apr 19, 2017 at 01:03:59PM -0400, Keith Busch wrote:
> > If it's a divide by 0 as your last link indicates, that must mean there
> > are possible nodes, but have no CPUs, and those should be skipped. If
> > that's the case, the following should fix it, but I'm going to do some
> > more qemu testing with various CPU topologies to confirm.
> 
> I printed variables from my test host, I think this can help to
> investigate the issue:
> 
> irq_create_affinity_masks:116: vecs_to_assign 0 ncpus 2 extra_vecs 2 vecs_per_node 0 affv 2 curvec 2 nodes 1

That explains a lot. This setup wants 2 "pre_vectors", but I didn't
know that was even a thing. This should fix it:

---
diff --git a/kernel/irq/affinity.c b/kernel/irq/affinity.c
index d052947..eb8b689 100644
--- a/kernel/irq/affinity.c
+++ b/kernel/irq/affinity.c
@@ -98,13 +98,16 @@ irq_create_affinity_masks(int nvecs, const struct irq_affinity *affd)
 		int ncpus, v, vecs_to_assign, vecs_per_node;
 
 		/* Spread the vectors per node */
-		vecs_per_node = (affv - curvec) / nodes;
+		vecs_per_node = (affv - (curvec - affd->pre_vectors)) / nodes;
 
 		/* Get the cpus on this node which are in the mask */
 		cpumask_and(nmsk, cpu_online_mask, cpumask_of_node(n));
--

  reply	other threads:[~2017-04-19 21:44 UTC|newest]

Thread overview: 9+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2017-04-13 17:28 [PATCH] " Keith Busch
2017-04-13 21:46 ` [tip:irq/urgent] " tip-bot for Keith Busch
2017-04-19 16:20 ` Andrei Vagin
2017-04-19 17:03   ` Keith Busch
2017-04-19 19:11     ` Andrei Vagin
2017-04-19 19:53     ` Andrei Vagin
2017-04-19 21:53       ` Keith Busch [this message]
2017-04-19 22:32         ` Andrei Vagin
2017-04-19 22:45           ` Keith Busch

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