From: Ian Campbell <ian.campbell@citrix.com>
To: Tim Deegan <tim@xen.org>
Cc: xen-devel@lists.xenproject.org, Keir Fraser <keir@xen.org>,
David Vrabel <david.vrabel@citrix.com>,
Jan Beulich <JBeulich@suse.com>,
Stefano Stabellini <stefano.stabellini@eu.citrix.com>
Subject: Re: [PATCHv2 4/6] x86: provide xadd()
Date: Thu, 16 Apr 2015 13:55:27 +0100 [thread overview]
Message-ID: <1429188927.25195.122.camel@citrix.com> (raw)
In-Reply-To: <20150416124925.GC13441@deinos.phlegethon.org>
On Thu, 2015-04-16 at 13:49 +0100, Tim Deegan wrote:
> At 12:49 +0100 on 16 Apr (1429188559), Jan Beulich wrote:
> > >>> On 16.04.15 at 13:25, <tim@xen.org> wrote:
> > > But also: AFAICS the GCC builtin __sync_fetch_and_add() does almost
> > > exactly this (the difference being that those are also compiler
> > > barriers where this is only a CPU barrier). Should we be using it
> > > instead?
> >
> > I'm afraid that's useful only from gcc 4.5.x onwards; earlier versions
> > (on x86 at least) simply generate a function call relying on a library to
> > implement it.
>
> Darn. :(
Might it still be a better generic fallback than the C/cmpxchg one?
On x86 you'd get the asm version, and on ARM you need 4.5.x onwards
anyway, plus in general the ARM folks seem to recommend using the
builtins more anyway.
Ian.
next prev parent reply other threads:[~2015-04-16 13:05 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2015-04-10 14:19 [PATCHv2 0/6] Use ticket locks for spinlocks David Vrabel
2015-04-10 14:19 ` [PATCHv2 1/6] x86/hvm: don't include asm/spinlock.h David Vrabel
2015-04-10 15:24 ` Andrew Cooper
2015-04-13 13:13 ` David Vrabel
2015-04-13 13:15 ` Andrew Cooper
2015-04-16 11:09 ` Tim Deegan
2015-04-10 14:19 ` [PATCHv2 2/6] x86/mtrr: include asm/atomic.h David Vrabel
2015-04-10 15:25 ` Andrew Cooper
2015-04-16 11:10 ` Tim Deegan
2015-04-10 14:19 ` [PATCHv2 3/6] xen: generic xadd() for ticket locks David Vrabel
2015-04-14 13:17 ` Ian Campbell
2015-04-14 16:37 ` David Vrabel
2015-04-15 8:34 ` Ian Campbell
2015-04-16 11:13 ` Tim Deegan
2015-04-16 15:28 ` Jan Beulich
2015-04-17 12:32 ` Ian Campbell
2015-04-17 12:33 ` Ian Campbell
2015-04-17 12:34 ` David Vrabel
2015-04-17 13:09 ` Ian Campbell
2015-04-17 13:13 ` David Vrabel
2015-04-10 14:19 ` [PATCHv2 4/6] x86: provide xadd() David Vrabel
2015-04-16 11:25 ` Tim Deegan
2015-04-16 11:38 ` David Vrabel
2015-04-16 11:41 ` Tim Deegan
2015-04-16 11:49 ` Jan Beulich
2015-04-16 12:49 ` Tim Deegan
2015-04-16 12:55 ` Ian Campbell [this message]
2015-04-16 13:19 ` Jan Beulich
2015-04-16 14:07 ` Ian Campbell
2015-04-16 14:09 ` Ian Campbell
2015-04-16 12:00 ` Ian Campbell
2015-04-10 14:19 ` [PATCHv2 5/6] xen: use ticket locks for spin locks David Vrabel
2015-04-10 15:29 ` Andrew Cooper
2015-04-10 16:44 ` Boris Ostrovsky
2015-04-10 17:29 ` David Vrabel
2015-04-10 17:58 ` Boris Ostrovsky
2015-04-16 12:03 ` Tim Deegan
2015-04-16 12:46 ` David Vrabel
2015-04-16 12:50 ` Tim Deegan
2015-04-16 13:32 ` Jan Beulich
2015-04-21 9:59 ` David Vrabel
2015-04-10 14:19 ` [PATCHv2 6/6] x86, arm: remove asm/spinlock.h from all architectures David Vrabel
2015-04-16 12:51 ` Tim Deegan
2015-04-16 15:29 ` Jan Beulich
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