From: "liwei (GF)" <liwei391@huawei.com>
To: Alex Kogan <alex.kogan@oracle.com>, <linux@armlinux.org.uk>,
<peterz@infradead.org>, <mingo@redhat.com>, <will.deacon@arm.com>,
<arnd@arndb.de>, <longman@redhat.com>,
<linux-arch@vger.kernel.org>,
<linux-arm-kernel@lists.infradead.org>,
<linux-kernel@vger.kernel.org>, <tglx@linutronix.de>,
<bp@alien8.de>, <hpa@zytor.com>, <x86@kernel.org>
Cc: <dave.dice@oracle.com>, <rahul.x.yadav@oracle.com>,
<steven.sistare@oracle.com>, <daniel.m.jordan@oracle.com>
Subject: Re: [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock
Date: Tue, 11 Jun 2019 12:22:05 +0800 [thread overview]
Message-ID: <cc3eee8c-5212-7af5-c932-897ab8f3f8bf@huawei.com> (raw)
In-Reply-To: <20190329152006.110370-4-alex.kogan@oracle.com>
Hi Alex,
On 2019/3/29 23:20, Alex Kogan wrote:
> In CNA, 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. At the unlock time,
> the lock holder scans the main queue looking for a thread running on
> the same node. 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, and the lock is passed to T. If such T is not found, the
> lock is passed to the first node in the secondary queue. Finally, if the
> secondary queue is empty, the lock is passed to the next thread in the
> main queue. For more details, see https://arxiv.org/abs/1810.05600.
>
> Note that this variant of CNA may introduce starvation by continuously
> passing the lock to threads running on the same node. This issue
> will be addressed later in the series.
>
> Enabling CNA is controlled via a new configuration option
> (NUMA_AWARE_SPINLOCKS), which is enabled by default if NUMA is enabled.
>
> Signed-off-by: Alex Kogan <alex.kogan@oracle.com>
> Reviewed-by: Steve Sistare <steven.sistare@oracle.com>
> ---
> arch/x86/Kconfig | 14 +++
> include/asm-generic/qspinlock_types.h | 13 +++
> kernel/locking/mcs_spinlock.h | 10 ++
> kernel/locking/qspinlock.c | 29 +++++-
> kernel/locking/qspinlock_cna.h | 173 ++++++++++++++++++++++++++++++++++
> 5 files changed, 236 insertions(+), 3 deletions(-)
> create mode 100644 kernel/locking/qspinlock_cna.h
>
(SNIP)
> +
> +static __always_inline int get_node_index(struct mcs_spinlock *node)
> +{
> + return decode_count(node->node_and_count++);
When nesting level is > 4, it won't return a index >= 4 here and the numa node number
is changed by mistake. It will go into a wrong way instead of the following branch.
/*
* 4 nodes are allocated based on the assumption that there will
* not be nested NMIs taking spinlocks. That may not be true in
* some architectures even though the chance of needing more than
* 4 nodes will still be extremely unlikely. When that happens,
* we fall back to spinning on the lock directly without using
* any MCS node. This is not the most elegant solution, but is
* simple enough.
*/
if (unlikely(idx >= MAX_NODES)) {
while (!queued_spin_trylock(lock))
cpu_relax();
goto release;
}
> +}
> +
> +static __always_inline void release_mcs_node(struct mcs_spinlock *node)
> +{
> + __this_cpu_dec(node->node_and_count);
> +}
> +
> +static __always_inline void cna_init_node(struct mcs_spinlock *node, int cpuid,
> + u32 tail)
> +{
Thanks,
Wei
next prev parent reply other threads:[~2019-06-11 4:22 UTC|newest]
Thread overview: 38+ messages / expand[flat|nested] mbox.gz Atom feed top
2019-03-29 15:20 [PATCH v2 0/5] Add NUMA-awareness to qspinlock Alex Kogan
2019-03-29 15:20 ` [PATCH v2 1/5] locking/qspinlock: Make arch_mcs_spin_unlock_contended more generic Alex Kogan
2019-03-29 15:20 ` [PATCH v2 2/5] locking/qspinlock: Refactor the qspinlock slow path Alex Kogan
2019-03-29 15:20 ` [PATCH v2 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2019-04-01 9:06 ` Peter Zijlstra
2019-04-01 9:33 ` Peter Zijlstra
2019-04-03 15:53 ` Alex Kogan
2019-04-03 16:10 ` Peter Zijlstra
2019-04-01 9:21 ` Peter Zijlstra
2019-04-01 14:36 ` Waiman Long
2019-04-02 9:43 ` Peter Zijlstra
2019-04-03 15:39 ` Alex Kogan
2019-04-03 15:48 ` Waiman Long
2019-04-03 16:01 ` Peter Zijlstra
2019-04-04 5:05 ` Juergen Gross
2019-04-04 9:38 ` Peter Zijlstra
2019-04-04 18:03 ` Waiman Long
2019-06-04 23:21 ` Alex Kogan
2019-06-05 20:40 ` Peter Zijlstra
2019-06-06 15:21 ` Alex Kogan
2019-06-06 15:32 ` Waiman Long
2019-06-06 15:42 ` Waiman Long
2019-04-03 16:33 ` Waiman Long
2019-04-03 17:16 ` Peter Zijlstra
2019-04-03 17:40 ` Waiman Long
2019-04-04 2:02 ` Hanjun Guo
2019-04-04 3:14 ` Alex Kogan
2019-06-11 4:22 ` liwei (GF) [this message]
2019-06-12 4:38 ` Alex Kogan
2019-06-12 15:05 ` Waiman Long
2019-03-29 15:20 ` [PATCH v2 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Alex Kogan
2019-04-02 10:37 ` Peter Zijlstra
2019-04-03 17:06 ` Alex Kogan
2019-03-29 15:20 ` [PATCH v2 5/5] locking/qspinlock: Introduce the shuffle reduction optimization " Alex Kogan
2019-04-01 9:09 ` [PATCH v2 0/5] Add NUMA-awareness to qspinlock Peter Zijlstra
2019-04-03 17:13 ` Alex Kogan
2019-07-03 11:58 ` Jan Glauber
2019-07-12 8:12 ` Hanjun Guo
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