Re: [PATCH v8 0/5] Add NUMA-awareness to qspinlock

Shijith Thotton
2020-01-21T09:21:56Z

Hi Will/Catalin,

On Wed, Jan 08, 2020 at 05:09:05AM +0000, Shijith Thotton wrote:
> On Mon, Dec 30, 2019 at 02:40:37PM -0500, Alex Kogan wrote:
> > Minor changes from v7 based on feedback from Longman:
> > -----------------------------------------------------
> >
> > - Move __init functions from alternative.c to qspinlock_cna.h
> >
> > - Introduce enum for return values from cna_pre_scan(), for better
> > readability.
> >
> > - Add/revise a few comments to improve readability.
> >
> >
> > Summary
> > -------
> >
> > Lock throughput can be increased by handing a lock to a waiter on the
> > same NUMA node as the lock holder, provided care is taken to avoid
> > starvation of waiters on other NUMA nodes. This patch introduces CNA
> > (compact NUMA-aware lock) as the slow path for qspinlock. It is
> > enabled through a configuration option (NUMA_AWARE_SPINLOCKS).
> >
> > CNA is a NUMA-aware version of the MCS lock. Spinning threads are
> > organized in two queues, a main queue for threads running on the same
> > node as the current lock holder, and a secondary queue for threads
> > running on other nodes. Threads store the ID of the node on which
> > they are running in their queue nodes. After acquiring the MCS lock and
> > before acquiring the spinlock, the lock holder scans the main queue
> > looking for a thread running on the same node (pre-scan). If found (call
> > it thread T), all threads in the main queue between the current lock
> > holder and T are moved to the end of the secondary queue. If such T
> > is not found, we make another scan of the main queue after acquiring
> > the spinlock when unlocking the MCS lock (post-scan), starting at the
> > node where pre-scan stopped. If both scans fail to find such T, the
> > MCS lock is passed to the first thread in the secondary queue. If the
> > secondary queue is empty, the MCS lock is passed to the next thread in the
> > main queue. To avoid starvation of threads in the secondary queue, those
> > threads are moved back to the head of the main queue after a certain
> > number of intra-node lock hand-offs.
> >
> > More details are available at https://urldefense.proofpoint.com/v2/url?u=https-3A__arxiv.org_abs_1810.05600&d=DwIDAg&c=nKjWec2b6R0mOyPaz7xtfQ&r=G9w4KsPaQLACBfGCL35PtiRH996yqJDxAZwrWegU2qQ&m=AoOLTQlgNjtdBvY_yWd6ViBXrVM6o2wqXOdFA4B_F2A&s=yUjG9gfi3BtLKDEjgki86h52GVXMvDQ6ZClMvoIG034&e= .
> >
> > The series applies on top of v5.5.0-rc2, commit ea200dec51.
> > Performance numbers are available in previous revisions
> > of the series.
> >
> > Further comments are welcome and appreciated.
> >
> > Alex Kogan (5):
> > locking/qspinlock: Rename mcs lock/unlock macros and make them more
> > generic
> > locking/qspinlock: Refactor the qspinlock slow path
> > locking/qspinlock: Introduce CNA into the slow path of qspinlock
> > locking/qspinlock: Introduce starvation avoidance into CNA
> > locking/qspinlock: Introduce the shuffle reduction optimization into
> > CNA
> >
> > .../admin-guide/kernel-parameters.txt | 18 +
> > arch/arm/include/asm/mcs_spinlock.h | 6 +-
> > arch/x86/Kconfig | 20 +
> > arch/x86/include/asm/qspinlock.h | 4 +
> > arch/x86/kernel/alternative.c | 4 +
> > include/asm-generic/mcs_spinlock.h | 4 +-
> > kernel/locking/mcs_spinlock.h | 20 +-
> > kernel/locking/qspinlock.c | 82 +++-
> > kernel/locking/qspinlock_cna.h | 400 ++++++++++++++++++
> > kernel/locking/qspinlock_paravirt.h | 2 +-
> > 10 files changed, 537 insertions(+), 23 deletions(-)
> > create mode 100644 kernel/locking/qspinlock_cna.h
> >
> > --
> > 2.21.0 (Apple Git-122.2)
> >
>
> Tried out queued spinlock slowpath improvements on arm64 (ThunderX2) by
> hardwiring CNA APIs to queued_spin_lock_slowpath() and numbers are pretty
> good with the CNA changes.
>
> Speed-up on v5.5-rc4 kernel:
>
> will-it-scale/open1_threads:
> #thr speed-up
> 1 1.00
> 2 0.97
> 4 0.98
> 8 1.02
> 16 0.95
> 32 1.63
> 64 1.70
> 128 2.09
> 224 2.16
>
> will-it-scale/lock2_threads:
> #thr speed-up
> 1 0.98
> 2 0.99
> 4 0.90
> 8 0.98
> 16 0.99
> 32 1.52
> 64 2.31
> 128 2.25
> 224 2.04
>
> #thr - number of threads
> speed-up - number with CNA patch / number with stock kernel
>
> Please share your thoughts on best way to enable this series on arm64.

Please comment if you got a chance to look at this.

Thanks,
Shijith