From: Peter Zijlstra <peterz@infradead.org>
To: David Howells <dhowells@redhat.com>
Cc: Ingo Molnar <mingo@kernel.org>, Michal Hocko <mhocko@kernel.org>,
LKML <linux-kernel@vger.kernel.org>,
Ingo Molnar <mingo@redhat.com>,
Thomas Gleixner <tglx@linutronix.de>,
"H. Peter Anvin" <hpa@zytor.com>,
"David S. Miller" <davem@davemloft.net>,
Tony Luck <tony.luck@intel.com>,
Andrew Morton <akpm@linux-foundation.org>,
Chris Zankel <chris@zankel.net>,
Max Filippov <jcmvbkbc@gmail.com>,
x86@kernel.org, linux-alpha@vger.kernel.org,
linux-ia64@vger.kernel.org, linux-s390@vger.kernel.org,
linux-sh@vger.kernel.org, sparclinux@vger.kernel.org,
linux-xtensa@linux-xtensa.org, linux-arch@vger.kernel.org,
Michal Hocko <mhocko@suse.com>,
Linus Torvalds <torvalds@linux-foundation.org>,
"Paul E. McKenney" <paulmck@us.ibm.com>,
Jason Low <jason.low2@hpe.com>
Subject: Re: [RFC 10/12] x86, rwsem: simplify __down_write
Date: Thu, 9 Jun 2016 19:36:40 +0200 [thread overview]
Message-ID: <20160609173640.GX30154@twins.programming.kicks-ass.net> (raw)
In-Reply-To: <29355.1465483258@warthog.procyon.org.uk>
On Thu, Jun 09, 2016 at 03:40:58PM +0100, David Howells wrote:
> Peter Zijlstra <peterz@infradead.org> wrote:
>
> > Blergh; so looking at more asm there's still a few tricks we cannot do.
> > So while overall size is down, some paths do end up more expensive. (It
> > typically boils down to creative use of condition flags, which is very
> > hard in C)
>
> It can be done using ISO __atomic_fetch_add() and suchlike.
(ISO-C11, ISO as such is a bad abbreviation I think)
Maybe, but we're almost there with __GCC_ASM_FLAG_OUTPUTS__.
atomic_long_add_negative() can be made to do inc;j(n)s for __down_read.
the try_cmpxchg family you wanted to add independent from the ISO-C11
bits can do the cmpxchg-j(n)z for __down_{read,write}_trylock.
That only leaves us wanting an atomic_long_fetch_add_negative() for
__up_{read,write}().
Although I suppose, for this to be of use for our weakly ordered
friends, we need _relaxed versions of all that (so that _acquire and
_release variants are generated).
next prev parent reply other threads:[~2016-06-09 17:37 UTC|newest]
Thread overview: 31+ messages / expand[flat|nested] mbox.gz Atom feed top
2016-02-02 20:19 [RFC 0/12] introduce down_write_killable for rw_semaphore Michal Hocko
2016-02-02 20:19 ` [RFC 01/12] locking, rwsem: get rid of __down_write_nested Michal Hocko
2016-02-02 20:19 ` [RFC 02/12] locking, rwsem: drop explicit memory barriers Michal Hocko
2016-02-02 20:19 ` [RFC 03/12] locking, rwsem: introduce basis for down_write_killable Michal Hocko
2016-02-02 20:19 ` [RFC 04/12] alpha, rwsem: provide __down_write_killable Michal Hocko
2016-02-02 20:19 ` [RFC 05/12] ia64, " Michal Hocko
2016-02-02 20:19 ` [RFC 06/12] s390, " Michal Hocko
2016-02-02 20:19 ` [RFC 07/12] sh, " Michal Hocko
2016-02-03 11:19 ` Sergei Shtylyov
2016-02-03 12:11 ` Michal Hocko
2016-02-02 20:19 ` [RFC 08/12] sparc, " Michal Hocko
2016-02-02 20:19 ` [RFC 09/12] xtensa, " Michal Hocko
2016-02-02 20:19 ` [RFC 10/12] x86, rwsem: simplify __down_write Michal Hocko
2016-02-03 8:10 ` Ingo Molnar
2016-02-03 12:10 ` Michal Hocko
2016-06-03 16:13 ` Peter Zijlstra
2016-06-03 22:34 ` Peter Zijlstra
2016-06-09 14:40 ` David Howells
2016-06-09 17:36 ` Peter Zijlstra [this message]
2016-06-10 16:39 ` Paul E. McKenney
2016-02-02 20:19 ` [RFC 11/12] x86, rwsem: provide __down_write_killable Michal Hocko
2016-02-17 16:41 ` [RFC 11/12 v1] " Michal Hocko
2016-02-02 20:19 ` [RFC 12/12] locking, rwsem: provide down_write_killable Michal Hocko
2016-02-19 12:15 ` [RFC 0/12] introduce down_write_killable for rw_semaphore Michal Hocko
2016-03-09 12:18 ` Ingo Molnar
2016-03-09 12:56 ` Michal Hocko
2016-03-09 13:17 ` Ingo Molnar
2016-03-09 13:28 ` Michal Hocko
2016-03-09 13:43 ` Ingo Molnar
2016-03-09 14:41 ` Michal Hocko
2016-03-10 10:24 ` Ingo Molnar
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