From: Davidlohr Bueso <dave@stgolabs.net>
To: Peter Zijlstra <peterz@infradead.org>
Cc: Linus Torvalds <torvalds@linux-foundation.org>,
Boqun Feng <boqun.feng@gmail.com>,
Manfred Spraul <manfred@colorfullife.com>,
Waiman Long <Waiman.Long@hpe.com>, Ingo Molnar <mingo@kernel.org>,
ggherdovich@suse.com, Mel Gorman <mgorman@techsingularity.net>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Paul McKenney <paulmck@linux.vnet.ibm.com>,
Will Deacon <will.deacon@arm.com>
Subject: Re: sem_lock() vs qspinlocks
Date: Sat, 21 May 2016 10:14:35 -0700 [thread overview]
Message-ID: <20160521171435.GB6899@linux-uzut.site> (raw)
In-Reply-To: <20160521073739.GB15728@worktop.ger.corp.intel.com>
On Sat, 21 May 2016, Peter Zijlstra wrote:
>On Fri, May 20, 2016 at 05:48:39PM -0700, Davidlohr Bueso wrote:
>> On Fri, 20 May 2016, Linus Torvalds wrote:
>>
>>
>> >Oh, I definitely agree on the stable part, and yes, the "splt things
>> >up" model should come later if people agree that it's a good thing.
>>
>> The backporting part is quite nice, yes, but ultimately I think I prefer
>> Linus' suggestion making things explicit, as opposed to consulting the spinlock
>> implying barriers. I also hate to have an smp_mb() (particularly for spin_is_locked)
>> given that we are not optimizing for the common case (regular mutual excl).
>
>I'm confused; we _are_ optimizing for the common case. spin_is_locked()
>is very unlikely to be used. And arguably should be used less in favour
>of lockdep_assert_held().
Indeed we are.
But by 'common case' I was really thinking about spin_is_locked() vs spin_wait_unlock().
The former being the more common of the two, and the one which mostly will _not_ be used
for lock correctness purposes, hence it doesn't need that new smp_mb. Hence allowing users
to explicitly set the ordering needs (ie spin_lock_synchronize()) seems like the better
long term alternative. otoh, with your approach all such bugs are automatically fixed :)
Thanks,
Davidlohr
next prev parent reply other threads:[~2016-05-21 17:14 UTC|newest]
Thread overview: 41+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-05-20 5:39 sem_lock() vs qspinlocks Davidlohr Bueso
2016-05-20 7:49 ` Peter Zijlstra
2016-05-20 15:00 ` Davidlohr Bueso
2016-05-20 15:05 ` Peter Zijlstra
2016-05-20 15:25 ` Davidlohr Bueso
2016-05-20 15:28 ` Peter Zijlstra
2016-05-20 20:47 ` Waiman Long
2016-05-20 20:52 ` Peter Zijlstra
2016-05-21 0:59 ` Davidlohr Bueso
2016-05-21 4:01 ` Waiman Long
2016-05-21 7:40 ` Peter Zijlstra
2016-05-20 7:53 ` Peter Zijlstra
2016-05-20 8:13 ` Peter Zijlstra
2016-05-20 8:18 ` Peter Zijlstra
2016-05-20 9:07 ` Giovanni Gherdovich
2016-05-20 9:34 ` Peter Zijlstra
2016-05-20 8:30 ` Peter Zijlstra
2016-05-20 9:00 ` Peter Zijlstra
2016-05-20 10:09 ` Ingo Molnar
2016-05-20 10:45 ` Mel Gorman
2016-05-20 11:58 ` Peter Zijlstra
2016-05-20 14:05 ` Boqun Feng
2016-05-20 15:21 ` Peter Zijlstra
2016-05-20 16:04 ` Peter Zijlstra
2016-05-20 17:00 ` Linus Torvalds
2016-05-20 21:06 ` Peter Zijlstra
2016-05-20 21:44 ` Linus Torvalds
2016-05-21 0:48 ` Davidlohr Bueso
2016-05-21 2:30 ` Linus Torvalds
2016-05-21 7:37 ` Peter Zijlstra
2016-05-21 13:49 ` Manfred Spraul
2016-05-24 10:57 ` Peter Zijlstra
2016-05-21 17:14 ` Davidlohr Bueso [this message]
2016-05-23 12:25 ` Peter Zijlstra
2016-05-23 17:52 ` Linus Torvalds
2016-05-25 6:37 ` Boqun Feng
2016-05-22 8:43 ` Manfred Spraul
2016-05-22 9:38 ` Peter Zijlstra
2016-05-20 16:20 ` Davidlohr Bueso
2016-05-20 20:44 ` Waiman Long
2016-05-20 20:53 ` Peter Zijlstra
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=20160521171435.GB6899@linux-uzut.site \
--to=dave@stgolabs.net \
--cc=Waiman.Long@hpe.com \
--cc=boqun.feng@gmail.com \
--cc=ggherdovich@suse.com \
--cc=linux-kernel@vger.kernel.org \
--cc=manfred@colorfullife.com \
--cc=mgorman@techsingularity.net \
--cc=mingo@kernel.org \
--cc=paulmck@linux.vnet.ibm.com \
--cc=peterz@infradead.org \
--cc=torvalds@linux-foundation.org \
--cc=will.deacon@arm.com \
/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).