On 9/22/21 3:25 PM, Davidlohr Bueso wrote:

On Fri, 14 May 2021, Alex Kogan wrote:

quoted

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.

quoted

+            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.

quoted

+    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


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