From: kemi <kemi.wang@intel.com>
To: Torvald Riegel <triegel@redhat.com>,
Rich Felker <dalias@libc.org>, "H.J. Lu" <hjl.tools@gmail.com>
Cc: Ma Ling <ling.ma.program@gmail.com>,
GNU C Library <libc-alpha@sourceware.org>,
"Lu, Hongjiu" <hongjiu.lu@intel.com>,
"ling.ma" <ling.ml@antfin.com>, Wei Xiao <wei3.xiao@intel.com>
Subject: Re: [PATCH] NUMA spinlock [BZ #23962]
Date: Tue, 15 Jan 2019 02:33:00 -0000 [thread overview]
Message-ID: <0b4620c1-a9c5-061e-9636-65d80655a6fd@intel.com> (raw)
In-Reply-To: <5c2bf8859a412759aba26a21b317ea98f6ff8eaf.camel@redhat.com>
>> "Scalable spinlock" is something of an oxymoron.
>
> No, that's not true at all. Most high-performance shared-memory
> synchronization constructs (on typical HW we have today) will do some kind
> of spinning (and back-off), and there's nothing wrong about it. This can
> scale very well.
>
>> Spinlocks are for
>> situations where contention is extremely rare,
>
> No, the question is rather whether the program needs blocking through the
> OS (for performance, or for semantics such as PI) or not. Energy may be
> another factor. For example, glibc's current mutexes don't scale well on
> short critical because there's not enough spinning being done.
>
yes. That's why we need pthread.mutex.spin_count tunable interface before.
But, that's not enough. When tunable is not the bottleneck, the simple busy-waiting
algorithm of current adaptive mutex is the major negative factor which degrades mutex
performance. That's why I proposed to use MCS-based spinning-waiting algorithm for adaptive
mutex.
https://sourceware.org/ml/libc-alpha/2019-01/msg00279.html
Also, if with very small critical section in the worklad, this new type of mutex
with GNU extension PTHREAD_MUTEX_QUEUESPINNER_NP acts like MCS-spinlock, and performs
much better than original spinlock.
So, in some day, if adaptive mutex is tuned good enough, it should act like
mcs-spinlock (or NUMA spinlock) if workload has small critical section, and
performs like normal mutex if the critical section is too big to spinning-wait.
next prev parent reply other threads:[~2019-01-15 2:33 UTC|newest]
Thread overview: 39+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-12-26 9:51 Ma Ling
2019-01-03 4:05 ` 马凌(彦军)
[not found] ` <0a474516-b8c8-48cf-aeea-e57c77b78cbd.ling.ml@antfin.com>
2019-01-03 5:35 ` 转发:[PATCH] " 马凌(彦军)
2019-01-03 14:52 ` Szabolcs Nagy
2019-01-03 19:59 ` H.J. Lu
2019-01-05 12:34 ` [PATCH] " Carlos O'Donell
2019-01-05 16:36 ` H.J. Lu
2019-01-07 19:12 ` Florian Weimer
2019-01-07 19:49 ` H.J. Lu
2019-01-10 16:31 ` Carlos O'Donell
2019-01-10 16:32 ` Florian Weimer
2019-01-10 16:41 ` Carlos O'Donell
2019-01-10 17:52 ` Szabolcs Nagy
2019-01-10 19:24 ` Carlos O'Donell
2019-01-11 12:01 ` kemi
2019-01-14 22:45 ` Torvald Riegel
2019-01-15 9:32 ` Florian Weimer
2019-01-15 12:01 ` Torvald Riegel
2019-01-15 12:17 ` Florian Weimer
2019-01-15 12:31 ` Torvald Riegel
2019-01-11 16:24 ` H.J. Lu
2019-01-14 23:03 ` Torvald Riegel
2019-01-04 4:13 ` 转发:[PATCH] " 马凌(彦军)
2019-01-03 20:43 ` [PATCH] " Rich Felker
2019-01-03 20:55 ` H.J. Lu
2019-01-03 21:21 ` Rich Felker
2019-01-03 21:28 ` H.J. Lu
2019-01-14 23:18 ` Torvald Riegel
2019-01-15 2:33 ` kemi [this message]
2019-01-15 12:37 ` Torvald Riegel
2019-01-15 16:44 ` Rich Felker
2019-01-17 3:10 ` kemi
2019-02-04 17:23 ` Torvald Riegel
2019-01-14 22:40 ` Torvald Riegel
2019-01-14 23:26 ` Torvald Riegel
2019-01-15 4:47 ` 马凌(彦军)
2019-01-15 2:56 ` kemi
2019-01-15 4:27 ` 马凌(彦军)
2019-01-10 13:18 马凌(彦军)
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