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SubjectRe: [PATCH v11 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock
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On 9/15/20 2:05 PM, Alex Kogan wrote:
> In CNA, spinning threads are organized in two queues, a primary queue for
> threads running on the same node as the current lock holder, and a
> secondary queue for threads running on other nodes. After acquiring the
> MCS lock and before acquiring the spinlock, the MCS lock
> holder checks whether the next waiter in the primary queue (if exists) is
> running on the same NUMA node. If it is not, that waiter is detached from
> the main queue and moved into the tail of the secondary queue. This way,
> we gradually filter the primary queue, leaving only waiters running on
> the same preferred NUMA node. For more details, see
> https://arxiv.org/abs/1810.05600.
>
> Note that this variant of CNA may introduce starvation by continuously
> passing the lock between waiters in the main queue. This issue will be
> addressed later in the series.
>
> Enabling CNA is controlled via a new configuration option
> (NUMA_AWARE_SPINLOCKS). By default, the CNA variant is patched in at the
> boot time only if we run on a multi-node machine in native environment and
> the new config is enabled. (For the time being, the patching requires
> CONFIG_PARAVIRT_SPINLOCKS to be enabled as well. However, this should be
> resolved once static_call() is available.) This default behavior can be
> overridden with the new kernel boot command-line option
> "numa_spinlock=on/off" (default is "auto").
>
> Signed-off-by: Alex Kogan <alex.kogan@oracle.com>
> Reviewed-by: Steve Sistare <steven.sistare@oracle.com>
> Reviewed-by: Waiman Long <longman@redhat.com>
> ---
> .../admin-guide/kernel-parameters.txt | 10 +
> arch/x86/Kconfig | 20 ++
> arch/x86/include/asm/qspinlock.h | 4 +
> arch/x86/kernel/alternative.c | 4 +
> kernel/locking/mcs_spinlock.h | 2 +-
> kernel/locking/qspinlock.c | 42 ++-
> kernel/locking/qspinlock_cna.h | 336 ++++++++++++++++++
> 7 files changed, 413 insertions(+), 5 deletions(-)
> create mode 100644 kernel/locking/qspinlock_cna.h
>
> diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt
> index a1068742a6df..51ce050f8701 100644
> --- a/Documentation/admin-guide/kernel-parameters.txt
> +++ b/Documentation/admin-guide/kernel-parameters.txt
> @@ -3353,6 +3353,16 @@
>
> nox2apic [X86-64,APIC] Do not enable x2APIC mode.
>
> + 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.
> + off - Unconditionally disable this variant.
> +
> + Not specifying this option is equivalent to
> + numa_spinlock=auto.
> +
> cpu0_hotplug [X86] Turn on CPU0 hotplug feature when
> CONFIG_BOOTPARAM_HOTPLUG_CPU0 is off.
> Some features depend on CPU0. Known dependencies are:

You will have to move down this hunk according to alphabetic order.
Other than that this patch looks good to me.

Cheers,
Longman

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