From: Peter Zijlstra <peterz@infradead.org>
To: Waiman Long <waiman.long@hp.com>
Cc: Thomas Gleixner <tglx@linutronix.de>,
Ingo Molnar <mingo@redhat.com>, "H. Peter Anvin" <hpa@zytor.com>,
Arnd Bergmann <arnd@arndb.de>,
linux-arch@vger.kernel.org, x86@kernel.org,
linux-kernel@vger.kernel.org,
Steven Rostedt <rostedt@goodmis.org>,
Andrew Morton <akpm@linux-foundation.org>,
Michel Lespinasse <walken@google.com>,
Andi Kleen <andi@firstfloor.org>, Rik van Riel <riel@redhat.com>,
"Paul E. McKenney" <paulmck@linux.vnet.ibm.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
Raghavendra K T <raghavendra.kt@linux.vnet.ibm.com>,
George Spelvin <linux@horizon.com>,
Tim Chen <tim.c.chen@linux.intel.com>,
aswin@hp.com, Scott J Norton <scott.norton@hp.com>
Subject: Re: [PATCH v11 0/4] Introducing a queue read/write lock implementation
Date: Fri, 31 Jan 2014 21:14:01 +0100 [thread overview]
Message-ID: <20140131201401.GD2936@laptop.programming.kicks-ass.net> (raw)
In-Reply-To: <52EBF276.1020505@hp.com>
On Fri, Jan 31, 2014 at 01:59:02PM -0500, Waiman Long wrote:
> On 01/31/2014 04:26 AM, Peter Zijlstra wrote:
> >On Thu, Jan 30, 2014 at 04:17:15PM +0100, Peter Zijlstra wrote:
> >>The below is still small and actually works.
> >OK, so having actually worked through the thing; I realized we can
> >actually do a version without MCS lock and instead use a ticket lock for
> >the waitqueue.
> >
> >This is both smaller (back to 8 bytes for the rwlock_t), and should be
> >faster under moderate contention for not having to touch extra
> >cachelines.
> >
> >Completely untested and with a rather crude generic ticket lock
> >implementation to illustrate the concept:
> >
>
> Using a ticket lock instead will have the same scalability problem as the
> ticket spinlock as all the waiting threads will spin on the lock cacheline
> causing a lot of cache bouncing traffic.
A much more important point for me is that a fair rwlock has a _much_
better worst case behaviour than the current mess. That's the reason I
was interested in the qrwlock thing. Not because it can run contended on
a 128 CPU system and be faster at being contended.
If you contend a lock with 128 CPUs you need to go fix that code that
causes this abysmal behaviour in the first place.
next prev parent reply other threads:[~2014-01-31 20:14 UTC|newest]
Thread overview: 33+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-01-24 4:28 [PATCH v11 0/4] Introducing a queue read/write lock implementation Waiman Long
2014-01-24 4:28 ` [PATCH v11 1/4] qrwlock: A " Waiman Long
2014-01-24 8:25 ` Peter Zijlstra
2014-01-25 4:39 ` Waiman Long
2014-01-24 4:28 ` [PATCH v11 2/4] qrwlock, x86: Enable x86 to use queue read/write lock Waiman Long
2014-01-24 4:28 ` [PATCH v11 3/4] qrwlock, x86: Add char and short as atomic data type in x86 Waiman Long
2014-01-24 4:28 ` [PATCH v11 4/4] qrwlock: Use the mcs_spinlock helper functions for MCS queuing Waiman Long
2014-01-24 8:26 ` Peter Zijlstra
2014-01-25 4:30 ` Waiman Long
2014-01-30 13:04 ` [PATCH v11 0/4] Introducing a queue read/write lock implementation Peter Zijlstra
2014-01-30 15:17 ` Peter Zijlstra
2014-01-30 15:43 ` Waiman Long
2014-01-30 15:50 ` Waiman Long
2014-01-30 15:53 ` Peter Zijlstra
2014-01-30 15:44 ` Peter Zijlstra
2014-01-30 17:52 ` Will Deacon
2014-01-30 18:05 ` Peter Zijlstra
2014-01-30 18:11 ` Will Deacon
2014-01-30 18:16 ` Peter Zijlstra
2014-01-31 9:26 ` Peter Zijlstra
2014-01-31 10:03 ` George Spelvin
2014-01-31 10:17 ` Peter Zijlstra
2014-01-31 11:30 ` Peter Zijlstra
2014-02-01 23:22 ` Paul E. McKenney
2014-01-31 18:59 ` Waiman Long
2014-01-31 19:47 ` Peter Zijlstra
2014-02-01 10:38 ` George Spelvin
2014-01-31 20:14 ` Peter Zijlstra [this message]
2014-01-31 21:09 ` Waiman Long
2014-02-01 1:29 ` Davidlohr Bueso
2014-02-02 9:03 ` Ingo Molnar
2014-02-03 11:38 ` Peter Zijlstra
2014-02-06 3:08 ` Waiman Long
Reply instructions:
You may reply publicly to this message via plain-text email
using any one of the following methods:
* Save the following mbox file, import it into your mail client,
and reply-to-all from there: mbox
Avoid top-posting and favor interleaved quoting:
https://en.wikipedia.org/wiki/Posting_style#Interleaved_style
* Reply using the --to, --cc, and --in-reply-to
switches of git-send-email(1):
git send-email \
--in-reply-to=20140131201401.GD2936@laptop.programming.kicks-ass.net \
--to=peterz@infradead.org \
--cc=akpm@linux-foundation.org \
--cc=andi@firstfloor.org \
--cc=arnd@arndb.de \
--cc=aswin@hp.com \
--cc=hpa@zytor.com \
--cc=linux-arch@vger.kernel.org \
--cc=linux-kernel@vger.kernel.org \
--cc=linux@horizon.com \
--cc=mingo@redhat.com \
--cc=paulmck@linux.vnet.ibm.com \
--cc=raghavendra.kt@linux.vnet.ibm.com \
--cc=riel@redhat.com \
--cc=rostedt@goodmis.org \
--cc=scott.norton@hp.com \
--cc=tglx@linutronix.de \
--cc=tim.c.chen@linux.intel.com \
--cc=torvalds@linux-foundation.org \
--cc=waiman.long@hp.com \
--cc=walken@google.com \
--cc=x86@kernel.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
Be sure your reply has a Subject: header at the top and a blank line
before the message body.
This is a public inbox, see mirroring instructions
for how to clone and mirror all data and code used for this inbox;
as well as URLs for NNTP newsgroup(s).