From: jamie@shareable•org (Jamie Lokier)
To: linux-arm-kernel@lists•infradead.org
Subject: [Kgdb-bugreport] [PATCH] ARM: change definition of cpu_relax() for ARM11MPCore
Date: Thu, 15 Apr 2010 22:03:22 +0100 [thread overview]
Message-ID: <20100415210322.GB26494@shareable.org> (raw)
In-Reply-To: <20100415173609.GA29752@mvista.com>
George G. Davis wrote:
> Hi,
>
> On Mon, Apr 12, 2010 at 06:32:47PM +0100, Russell King - ARM Linux wrote:
> > On Mon, Apr 12, 2010 at 06:23:58PM +0100, Will Deacon wrote:
> > > This patch changes the definition of cpu_relax() to smp_mb() for ARMv6 cores,
> > > forcing the write buffer to drain while inside a polling loop on an SMP system.
> > > If the Kernel is not compiled for SMP support, this will expand to a barrier()
> > > as before.
>
> If I've followed these threads [1][2] correctly, this ARM11 MPCore issue
> was discovered while running the "KGDB: internal test suite" (KGDB_TESTS)
> and that problem is resolved via "kgdb: use atomic_inc and atomic_dec
> instead of atomic_set" [3]. If so, isn't the original ARM11 MPCore KGDB
> cpu_relax() issue just a red herring? Shouldn't any polling loops
> which depend on specific (hardware) write/read order implement appropriate
> barriers rather than rely on cpu_relax() to guarantee order?
Note that the need to force the write buffer to drain is _not_ an
ordering issue. It's a buffer draining issue. :-)
I'm not sure if Linux smp_wmb() guarantees to ensure prior writes will
be visible to other CPUs in a short time, or if it only guarantees
write order.
-- Jamie
next prev parent reply other threads:[~2010-04-15 21:03 UTC|newest]
Thread overview: 13+ messages / expand[flat|nested] mbox.gz Atom feed top
2010-04-12 17:23 [PATCH] ARM: change definition of cpu_relax() for ARM11MPCore Will Deacon
2010-04-12 17:32 ` Russell King - ARM Linux
2010-04-15 17:36 ` [Kgdb-bugreport] " George G. Davis
2010-04-15 21:03 ` Jamie Lokier [this message]
2010-04-16 13:54 ` Will Deacon
2010-04-19 14:39 ` Will Deacon
-- strict thread matches above, loose matches on Subject: below --
2010-03-09 16:06 Will Deacon
2010-03-09 16:22 ` Russell King - ARM Linux
2010-03-09 16:35 ` Will Deacon
2010-03-09 16:49 ` Russell King - ARM Linux
2010-03-09 17:59 ` Will Deacon
2010-03-10 22:06 ` [Kgdb-bugreport] " Jason Wessel
2010-03-11 2:47 ` DDD
2010-03-11 13:53 ` Will Deacon
2010-03-11 13:29 ` Will Deacon
2010-03-11 14:51 ` Will Deacon
2010-03-16 17:26 ` Will Deacon
2010-03-16 18:52 ` Jason Wessel
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=20100415210322.GB26494@shareable.org \
--to=jamie@shareable$(echo .)org \
--cc=linux-arm-kernel@lists$(echo .)infradead.org \
/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