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Subject: Re: [PATCH v9 0/5] Add NUMA-awareness to qspinlock
To:     paulmck@kernel.org
Cc:     Alex Kogan <alex.kogan@oracle.com>, linux@armlinux.org.uk,
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From:   Waiman Long <longman@redhat.com>
Organization: Red Hat
Message-ID: <967f99ee-b781-43f4-d8ba-af83786c429c@redhat.com>
Date:   Sat, 25 Jan 2020 14:41:39 -0500
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On 1/24/20 11:58 PM, Paul E. McKenney wrote:
> On Fri, Jan 24, 2020 at 09:17:05PM -0500, Waiman Long wrote:
>> On 1/24/20 8:59 PM, Waiman Long wrote:
>>>> You called it!  I will play with QEMU's -numa argument to see if I can get
>>>> CNA to run for me.  Please accept my apologies for the false alarm.
>>>>
>>>> 							Thanx, Paul
>>>>
>>> CNA is not currently supported in a VM guest simply because the numa
>>> information is not reliable. You will have to run it on baremetal to
>>> test it. Sorry for that.
>> Correction. There is a command line option to force CNA lock to be used
>> in a VM. Use the "numa_spinlock=on" boot command line parameter.
> As I understand it, I need to use a series of -numa arguments to qemu
> combined with the numa_spinlock=on (or =1) on the kernel command line.
> If the kernel thinks that there is only one NUMA node, it appears to
> avoid doing CNA.
>
> Correct?
>
> 							Thanx, Paul
>
In auto-detection mode (the default), CNA will only be turned on when
paravirt qspinlock is not enabled first and there are at least 2 numa
nodes. The "numa_spinlock=on" option will force it on even when both of
the above conditions are false.

Cheers,
Longman