From: Gabriel Paubert <paubert@iram•es>
To: Paul Mackerras <paulus@samba•org>
Cc: Andrew Morton <akpm@osdl•org>,
Mathieu Desnoyers <mathieu.desnoyers@polymtl•ca>,
Greg Kroah-Hartman <gregkh@suse•de>,
linux-kernel@vger•kernel.org,
"Martin J. Bligh" <mbligh@mbligh•org>,
Christoph Hellwig <hch@infradead•org>,
linuxppc-dev@ozlabs•org, Douglas Niehaus <niehaus@eecs•ku.edu>,
Ingo Molnar <mingo@redhat•com>,
ltt-dev@shafik•org, systemtap@sources•redhat.com,
Thomas Gleixner <tglx@linutronix•de>
Subject: Re: [PATCH 7/10] local_t : powerpc
Date: Wed, 24 Jan 2007 11:43:13 +0100 [thread overview]
Message-ID: <20070124104313.GB22579@iram.es> (raw)
In-Reply-To: <17847.8700.118329.777644@cargo.ozlabs.ibm.com>
On Wed, Jan 24, 2007 at 08:08:12PM +1100, Paul Mackerras wrote:
> Mathieu Desnoyers writes:
>
> > +static __inline__ int local_dec_if_positive(local_t *l)
> > +{
> > + int t;
> > +
> > + __asm__ __volatile__(
> > +"1: lwarx %0,0,%1 # local_dec_if_positive\n\
> > + addic. %0,%0,-1\n\
> > + blt- 2f\n"
> > + PPC405_ERR77(0,%1)
> > +" stwcx. %0,0,%1\n\
> > + bne- 1b"
>
> This has the same bugs that we fixed recently in atomic_dec_if_positive;
> first, on 64-bit machines, the lwarx will zero-extend the word loaded
> from memory, and so the result of the addic will be negative only if
> the word was originally 0. Secondly, even on 32-bit machines,
> 0x80000000 will be considered positive since decrementing it gives
> 0x7fffffff, which is positive.
>
> > +/* Use these for per-cpu local_t variables: on some archs they are
> > + * much more efficient than these naive implementations. Note they take
> > + * a variable, not an address.
> > + *
> > + * This could be done better if we moved the per cpu data directly
> > + * after GS.
> > + */
>
> What's "GS"? Does this comment really apply on powerpc?
>
1) It's an (application visible) i386/x86_64 segment register used
to make memory addressing more confusing.
2) Because of 1), obviously not ;-)
Gabriel
next prev parent reply other threads:[~2007-01-24 10:43 UTC|newest]
Thread overview: 5+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <20061221001545.GP28643@Krystal>
2006-12-21 0:27 ` [PATCH 7/10] local_t : powerpc Mathieu Desnoyers
2006-12-21 3:34 ` [Ltt-dev] " Mathieu Desnoyers
2007-01-24 9:08 ` Paul Mackerras
2007-01-24 10:43 ` Gabriel Paubert [this message]
2007-01-24 17:00 ` Mathieu Desnoyers
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=20070124104313.GB22579@iram.es \
--to=paubert@iram$(echo .)es \
--cc=akpm@osdl$(echo .)org \
--cc=gregkh@suse$(echo .)de \
--cc=hch@infradead$(echo .)org \
--cc=linux-kernel@vger$(echo .)kernel.org \
--cc=linuxppc-dev@ozlabs$(echo .)org \
--cc=ltt-dev@shafik$(echo .)org \
--cc=mathieu.desnoyers@polymtl$(echo .)ca \
--cc=mbligh@mbligh$(echo .)org \
--cc=mingo@redhat$(echo .)com \
--cc=niehaus@eecs$(echo .)ku.edu \
--cc=paulus@samba$(echo .)org \
--cc=systemtap@sources$(echo .)redhat.com \
--cc=tglx@linutronix$(echo .)de \
/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