From: Alex Kogan <alex.kogan@oracle.com>
To: Lihao Liang <lihaoliang@google.com>
Cc: linux-arch@vger.kernel.org, guohanjun@huawei.com, arnd@arndb.de,
Peter Zijlstra <peterz@infradead.org>,
dave.dice@oracle.com, jglauber@marvell.com, x86@kernel.org,
will.deacon@arm.com, linux@armlinux.org.uk,
steven.sistare@oracle.com, linux-kernel@vger.kernel.org,
mingo@redhat.com, bp@alien8.de, hpa@zytor.com,
longman@redhat.com, tglx@linutronix.de,
daniel.m.jordan@oracle.com, Will Deacon <will@kernel.org>,
linux-arm-kernel@lists.infradead.org
Subject: Re: [PATCH v9 0/5] Add NUMA-awareness to qspinlock
Date: Mon, 27 Jan 2020 01:16:36 -0500 [thread overview]
Message-ID: <3CBCD208-0859-458E-8A89-96E8E9A98664@oracle.com> (raw)
In-Reply-To: <CAC4j=Y_SMHe4WNpaaS0kK1JYfnufM+AAiwwUMBx27L8U6bD8Yg@mail.gmail.com>
>>> This is particularly relevant
>>> in high contention situations when new threads keep arriving on the same
>>> socket as the lock holder.
>> In this case, the lock will stay on the same NUMA node/socket for
>> 2^numa_spinlock_threshold times, which is the worst case scenario if we
>> consider the long-term fairness. And if we have multiple nodes, it will take
>> up to 2^numa_spinlock_threshold X (nr_nodes - 1) + nr_cpus_per_node
>> lock transitions until any given thread will acquire the lock
>> (assuming 2^numa_spinlock_threshold > nr_cpus_per_node).
>>
>
> You're right that the latest version of the patch handles long-term fairness
> deterministically.
>
> As I understand it, the n-th thread in the main queue is guaranteed to
> acquire the lock after N lock handovers, where N is bounded by
>
> n - 1 + 2^numa_spinlock_threshold * (nr_nodes - 1)
>
> I'm not sure what role the variable nr_cpus_per_node plays in your analysis.
Yeah, that’s a minor point, but let me try to clarify.
The "n-th thread in the main queue” is (at most) the nr_cpus_per_node-th thread
for some node k. So when the node k gets the preference, that thread will
get the lock after at most nr_cpus_per_node-1 lock transitions. As we consider
the upper bound, your analysis is also correct; mine is just a bit tighter.
Makes sense?
Regards,
— Alex
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next prev parent reply other threads:[~2020-01-27 6:17 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-01-15 3:59 [PATCH v9 0/5] Add NUMA-awareness to qspinlock Alex Kogan
2020-01-15 3:59 ` [PATCH v9 1/5] locking/qspinlock: Rename mcs lock/unlock macros and make them more generic Alex Kogan
2020-01-15 3:59 ` [PATCH v9 2/5] locking/qspinlock: Refactor the qspinlock slow path Alex Kogan
2020-01-15 3:59 ` [PATCH v9 3/5] locking/qspinlock: Introduce CNA into the slow path of qspinlock Alex Kogan
2020-01-23 9:26 ` Peter Zijlstra
2020-01-23 10:06 ` Peter Zijlstra
2020-01-23 10:16 ` Peter Zijlstra
2020-01-23 11:22 ` Will Deacon
2020-01-23 13:17 ` Peter Zijlstra
2020-01-23 14:15 ` Waiman Long
2020-01-23 15:29 ` Peter Zijlstra
2020-01-15 3:59 ` [PATCH v9 4/5] locking/qspinlock: Introduce starvation avoidance into CNA Alex Kogan
2020-01-23 19:55 ` Waiman Long
2020-01-23 20:39 ` Waiman Long
2020-01-23 23:39 ` Alex Kogan
2020-01-15 3:59 ` [PATCH v9 5/5] locking/qspinlock: Introduce the shuffle reduction optimization " Alex Kogan
2020-01-22 11:45 ` [PATCH v9 0/5] Add NUMA-awareness to qspinlock Lihao Liang
2020-01-22 17:24 ` Waiman Long
2020-01-23 11:35 ` Will Deacon
2020-01-23 15:25 ` Waiman Long
2020-01-23 19:08 ` Waiman Long
2020-01-22 19:29 ` Alex Kogan
2020-01-26 0:32 ` Lihao Liang
2020-01-26 1:58 ` Lihao Liang
2020-01-27 16:01 ` Alex Kogan
2020-01-29 1:39 ` Lihao Liang
2020-01-27 6:16 ` Alex Kogan [this message]
2020-01-24 22:24 ` Paul E. McKenney
[not found] ` <6AAE7FC6-F5DE-4067-8BC4-77F27948CD09@oracle.com>
2020-01-25 0:57 ` Paul E. McKenney
2020-01-25 1:59 ` Waiman Long
[not found] ` <adb4fb09-f374-4d64-096b-ba9ad8b35fd5@redhat.com>
2020-01-25 4:58 ` Paul E. McKenney
2020-01-25 19:41 ` Waiman Long
2020-01-26 15:35 ` Paul E. McKenney
2020-01-26 22:42 ` Paul E. McKenney
2020-01-26 23:32 ` Paul E. McKenney
2020-01-27 6:04 ` Alex Kogan
2020-01-27 14:11 ` Waiman Long
2020-01-27 15:09 ` Paul E. McKenney
[not found] ` <9b3a3f16-5405-b6d1-d023-b85f4aab46dd@redhat.com>
2020-01-27 17:17 ` Waiman Long
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