lkml.org 
[lkml]   [2021]   [Sep]   [22]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
From
SubjectRe: [PATCH v15 3/6] locking/qspinlock: Introduce CNA into the slow path of qspinlock
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

\
 
 \ /
  Last update: 2021-09-22 21:26    [W:0.209 / U:1.684 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site