From: Peter Zijlstra <peterz@infradead•org>
To: Torsten Duwe <duwe@lst•de>
Cc: Tom Musta <tommusta@gmail•com>,
linux-kernel@vger•kernel.org, Paul Mackerras <paulus@samba•org>,
Anton Blanchard <anton@samba•org>,
Scott Wood <scottwood@freescale•com>,
"Paul E. McKenney" <paulmck@linux•vnet.ibm.com>,
linuxppc-dev@lists•ozlabs.org, Ingo Molnar <mingo@kernel•org>
Subject: Re: [PATCH] Convert powerpc simple spinlocks into ticket locks
Date: Fri, 7 Feb 2014 16:43:46 +0100 [thread overview]
Message-ID: <20140207154346.GC3104@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <20140207151847.GB3104@twins.programming.kicks-ass.net>
On Fri, Feb 07, 2014 at 04:18:47PM +0100, Peter Zijlstra wrote:
> void ticket_lock(tickets_t *lock)
> {
> tickets_t t;
>
> /*
> * Because @head is MSB, the direct increment wrap doesn't disturb
> * @tail.
> */
> t.pair = xadd(&lock->pair, 1<<16);
>
> if (likely(t.head == t.tail)) {
> __lwsync(); /* acquire */
> return;
> }
>
> while (smp_load_acquire(&lock->tail) != t.tail)
> cpu_relax();
That should be "!= t.head", for that contains our ticket.
I'm hopelessly scatter brained today it seems :/
> }
>
> void ticket_unlock(tickets_t *lock)
> {
> ticket_t tail = lock->tail + 1;
>
> /*
> * The store is save against the xadd for it will make the ll/sc fail
> * and try again. Aside from that PowerISA guarantees single-copy
> * atomicy for half-word writes.
> *
> * And since only the lock owner will ever write the tail, we're good.
> */
> smp_store_release(&lock->tail, tail);
> }
next prev parent reply other threads:[~2014-02-07 15:43 UTC|newest]
Thread overview: 23+ messages / expand[flat|nested] mbox.gz Atom feed top
2014-02-06 10:37 [PATCH] Convert powerpc simple spinlocks into ticket locks Torsten Duwe
2014-02-06 15:53 ` Benjamin Herrenschmidt
2014-02-06 16:38 ` Peter Zijlstra
2014-02-06 17:37 ` Torsten Duwe
2014-02-06 18:08 ` Peter Zijlstra
2014-02-06 19:28 ` Tom Musta
2014-02-10 2:54 ` Benjamin Herrenschmidt
2014-02-07 8:24 ` Torsten Duwe
2014-02-06 20:19 ` Scott Wood
2014-02-07 9:02 ` Torsten Duwe
2014-02-07 10:31 ` Peter Zijlstra
2014-02-07 10:36 ` Peter Zijlstra
2014-02-07 10:45 ` Peter Zijlstra
2014-02-07 11:49 ` Torsten Duwe
2014-02-07 12:28 ` Peter Zijlstra
2014-02-07 15:18 ` Peter Zijlstra
2014-02-07 15:43 ` Peter Zijlstra [this message]
2014-02-07 17:08 ` Torsten Duwe
2014-02-07 17:19 ` Peter Zijlstra
2014-02-07 15:51 ` Kumar Gala
2014-02-07 16:10 ` Peter Zijlstra
2014-02-10 3:05 ` Benjamin Herrenschmidt
2014-02-10 3:02 ` Benjamin Herrenschmidt
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=20140207154346.GC3104@twins.programming.kicks-ass.net \
--to=peterz@infradead$(echo .)org \
--cc=anton@samba$(echo .)org \
--cc=duwe@lst$(echo .)de \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linuxppc-dev@lists$(echo .)ozlabs.org \
--cc=mingo@kernel$(echo .)org \
--cc=paulmck@linux$(echo .)vnet.ibm.com \
--cc=paulus@samba$(echo .)org \
--cc=scottwood@freescale$(echo .)com \
--cc=tommusta@gmail$(echo .)com \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
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