Messages in this thread | | | Date | Wed, 22 Sep 2021 12:25:28 -0700 | From | Davidlohr Bueso <> | Subject | Re: [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow path of qspinlock |
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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.
>+ 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.
>+ 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.
Thanks, Davidlohr
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