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From: Waiman Long <llong@redhat.com>
To: Davidlohr Bueso <dave@stgolabs.net>, Alex Kogan <alex.kogan@oracle.com>
Cc: linux@armlinux.org.uk, peterz@infradead.org, mingo@redhat.com,
	will.deacon@arm.com, arnd@arndb.de, linux-arch@vger.kernel.org,
	linux-arm-kernel@lists.infradead.org,
	linux-kernel@vger.kernel.org, tglx@linutronix.de, bp@alien8.de,
	hpa@zytor.com, x86@kernel.org, guohanjun@huawei.com,
	jglauber@marvell.com, steven.sistare@oracle.com,
	daniel.m.jordan@oracle.com, dave.dice@oracle.com
Subject: Re: [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow path of qspinlock
Date: Wed, 22 Sep 2021 15:52:18 -0400	[thread overview]
Message-ID: <8e743acb-ec75-ea03-493a-d57154ab8fed@redhat.com> (raw)
In-Reply-To: <20210922192528.ob22pu54oeqsoeno@offworld>

On 9/22/21 3:25 PM, Davidlohr Bueso wrote:
> On Fri, 14 May 2021, Alex Kogan wrote:
>
>> diff --git a/Documentation/admin-guide/kernel-parameters.txt 
>> b/Documentation/admin-guide/kernel-parameters.txt
>> index a816935d23d4..94d35507560c 100644
>> --- a/Documentation/admin-guide/kernel-parameters.txt
>> +++ b/Documentation/admin-guide/kernel-parameters.txt
>> @@ -3515,6 +3515,16 @@
>>             NUMA balancing.
>>             Allowed values are enable and disable
>>
>> +    numa_spinlock=    [NUMA, PV_OPS] Select the NUMA-aware variant
>> +            of spinlock. The options are:
>> +            auto - Enable this variant if running on a multi-node
>> +            machine in native environment.
>> +            on  - Unconditionally enable this variant.
>
> Is there any reason why the user would explicitly pass the on option
> when the auto thing already does the multi-node check? Perhaps strange
> numa topologies? Otherwise I would say it's not needed and the fewer
> options we give the user for low level locking the better.

I asked Alex to put in a command line option because we may want to 
disable it on a multi-socket server if we want to.


>
>> +            off - Unconditionally disable this variant.
>> +
>> +            Not specifying this option is equivalent to
>> +            numa_spinlock=auto.
>> +
>>     numa_zonelist_order= [KNL, BOOT] Select zonelist order for NUMA.
>>             'node', 'default' can be specified
>>             This can be set from sysctl after boot.
>> diff --git a/arch/x86/Kconfig b/arch/x86/Kconfig
>> index 0045e1b44190..819c3dad8afc 100644
>> --- a/arch/x86/Kconfig
>> +++ b/arch/x86/Kconfig
>> @@ -1564,6 +1564,26 @@ config NUMA
>>
>>       Otherwise, you should say N.
>>
>> +config NUMA_AWARE_SPINLOCKS
>> +    bool "Numa-aware spinlocks"
>> +    depends on NUMA
>> +    depends on QUEUED_SPINLOCKS
>> +    depends on 64BIT
>> +    # For now, we depend on PARAVIRT_SPINLOCKS to make the patching 
>> work.
>> +    # This is awkward, but hopefully would be resolved once 
>> static_call()
>> +    # is available.
>> +    depends on PARAVIRT_SPINLOCKS
>
> We now have static_call() - see 9183c3f9ed7.
I agree that it is now time to look at using the static call for 
slowpath switching.
>
>
>> +    default y
>> +    help
>> +      Introduce NUMA (Non Uniform Memory Access) awareness into
>> +      the slow path of spinlocks.
>> +
>> +      In this variant of qspinlock, the kernel will try to keep the 
>> lock
>> +      on the same node, thus reducing the number of remote cache 
>> misses,
>> +      while trading some of the short term fairness for better 
>> performance.
>> +
>> +      Say N if you want absolute first come first serve fairness.
>
> This would also need a depends on !PREEMPT_RT, no? Raw spinlocks 
> really want
> the determinism. 

Agreed

Cheers,
Longman


  reply	other threads:[~2021-09-22 19:52 UTC|newest]

Thread overview: 14+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-05-14 20:07 [PATCH v15 0/6] Add NUMA-awareness to qspinlock Alex Kogan
2021-05-14 20:07 ` [PATCH v15 1/6] locking/qspinlock: Rename mcs lock/unlock macros and make them more generic Alex Kogan
2021-05-14 20:07 ` [PATCH v15 2/6] locking/qspinlock: Refactor the qspinlock slow path Alex Kogan
2021-05-14 20:07 ` [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2021-09-22 19:25   ` Davidlohr Bueso
2021-09-22 19:52     ` Waiman Long [this message]
2021-09-30 10:05   ` Barry Song
2021-05-14 20:07 ` [PATCH v15 4/6] locking/qspinlock: Introduce starvation avoidance into CNA Alex Kogan
2021-05-14 20:07 ` [PATCH v15 5/6] locking/qspinlock: Avoid moving certain threads between waiting queues in CNA Alex Kogan
2021-05-14 20:07 ` [PATCH v15 6/6] locking/qspinlock: Introduce the shuffle reduction optimization into CNA Alex Kogan
2021-09-30  9:44 ` [PATCH v15 0/6] Add NUMA-awareness to qspinlock Barry Song
2021-09-30 16:58   ` Waiman Long
2021-09-30 22:57     ` Barry Song
2021-09-30 23:51   ` Alex Kogan

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