linux-kernel - Re: [PATCH v9 0/5] Add NUMA-awareness to qspinlock

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Date:   Sat, 25 Jan 2020 14:41:39 -0500
From:   Waiman Long <longman@...hat.com>
To:     paulmck@...nel.org
Cc:     Alex Kogan <alex.kogan@...cle.com>, linux@...linux.org.uk,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...hat.com>,
        Will Deacon <will.deacon@....com>,
        Arnd Bergmann <arnd@...db.de>, linux-arch@...r.kernel.org,
        linux-arm-kernel <linux-arm-kernel@...ts.infradead.org>,
        linux-kernel@...r.kernel.org, tglx@...utronix.de, bp@...en8.de,
        hpa@...or.com, x86@...nel.org, guohanjun@...wei.com,
        jglauber@...vell.com, dave.dice@...cle.com,
        steven.sistare@...cle.com, daniel.m.jordan@...cle.com
Subject: Re: [PATCH v9 0/5] Add NUMA-awareness to qspinlock

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