Re: [PATCH 4/4][RFC v2] x86/apic: Spread the vectors by choosing the idlest CPU

[Yu Chen <yu.c.chen@intel.com>]

On Wed, Sep 06, 2017 at 10:46:17AM -0700, Dan Williams wrote:
> On Tue, Sep 5, 2017 at 11:15 PM, Christoph Hellwig <hch@lst.de> wrote:
> > On Wed, Sep 06, 2017 at 12:13:38PM +0800, Yu Chen wrote:
> >> I agree, the driver could be rewritten, but it might take some time, so
> >> meanwhile I'm looking at also other possible optimization.
> >
> > Which driver are we talking about anyway?  Let's start looking at it
> > and fix the issue there.
> 
> As far as I understand, it's already fixed there:
> 
> commit 7c9ae7f053e9e896c24fd23595ba369a5fe322e1
> Author: Carolyn Wyborny <carolyn.wyborny@intel.com>
> Date:   Tue Jun 20 15:16:53 2017 -0700
> 
>     i40e: Fix for trace found with S4 state
> 
>     This patch fixes a problem found in systems when entering
>     S4 state.  This patch fixes the problem by ensuring that
>     the misc vector's IRQ is disabled as well.  Without this
>     patch a stack trace can be seen upon entering S4 state.
> 
> However this seems like something that should be handled generically
> in the irq-core especially since commit c5cb83bb337c
> "genirq/cpuhotplug: Handle managed IRQs on CPU hotplug" was headed in
> that direction. It's otherwise non-obvious when a driver needs to
> release and re-acquire interrupts or be reworked to use managed
> interrupts.
Yes, thanks for the explaination! I did not notice this patch has
been merged already.
I'm using the normal CPU hotplug to reproduce the issue:
#!/bin/bash

n=1

while [ $n -le 31 ]
do
	echo 0 > /sys/devices/system/cpu/cpu${n}/online
	n=$(( n+1 ))
done

Thanks,
	Yu