From: "David Schwartz" <davids@webmaster.com>
To: "Paul Mackerras" <paulus@samba.org>
Cc: <linux-kernel@vger.kernel.org>
Subject: RE: [PATCH] udev enhancements to use kernel event queue
Date: Fri, 13 Jun 2003 04:17:54 -0700 [thread overview]
Message-ID: <MDEHLPKNGKAHNMBLJOLKCEFJDKAA.davids@webmaster.com> (raw)
In-Reply-To: <16105.3943.510055.309447@nanango.paulus.ozlabs.org>
Pual Mackerras is said to have opined:
> Patrick Mochel writes:
> > +static inline int atomic_inc_and_read(atomic_t *v)
> > +{
> > + __asm__ __volatile__(
> > + LOCK "incl %0"
> > + :"=m" (v->counter)
> > + :"m" (v->counter));
> > + return v->counter;
> > +}
> BZZZT. If another CPU is also doing atomic_inc_and_read you could end
> up with both calls returning the same value.
>
> You can't do atomic_inc_and_read on 386. You can on cpus that have
> cmpxchg (e.g. later x86). You can also on machines with load-locked
> and store-conditional instructions (alpha, ppc, probably most other
> RISCs).
You can also do it with a conditional move instruction, but it's kind of
ugly. No help on a '386 though.
There are ways to do it that work on a 386, but they are all basically
equivalent to (or worse than) acquiring a spinlock, doing the deed, and then
releasing it.
You could also do (in pseudo-code):
top:
ret <- v->counter
inc ret
LOCK incl v->counter
cmp v->counter, ret
jz end
LOCK decl v->counter
jmp top:
end:
return ret
This does not strictly guarantee in order return values, but that's
meaningless without a lock anyway.
DS
next prev parent reply other threads:[~2003-06-13 11:04 UTC|newest]
Thread overview: 73+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-06-12 19:10 [PATCH] udev enhancements to use kernel event queue Steven Dake
2003-06-12 21:47 ` Patrick Mochel
2003-06-13 16:31 ` Steven Dake
2003-06-13 17:06 ` Patrick Mochel
2003-06-12 21:47 ` Greg KH
2003-06-12 22:03 ` Andrew Morton
2003-06-12 22:50 ` Greg KH
2003-06-12 22:51 ` Andrew Morton
2003-06-12 23:02 ` Greg KH
2003-06-12 23:09 ` Greg KH
2003-06-12 23:14 ` Patrick Mochel
2003-06-12 23:16 ` Robert Love
2003-06-12 23:25 ` Greg KH
2003-06-13 20:01 ` Oliver Neukum
2003-06-18 22:59 ` Greg KH
2003-06-19 0:12 ` Kevin P. Fleming
2003-06-19 0:20 ` Greg KH
2003-06-19 0:42 ` Kevin P. Fleming
2003-06-19 0:51 ` Greg KH
2003-06-19 0:25 ` Andrew Morton
2003-06-19 6:27 ` Oliver Neukum
2003-06-12 23:25 ` Patrick Mochel
2003-06-12 23:29 ` Robert Love
2003-06-12 23:32 ` Greg KH
2003-06-12 23:34 ` Patrick Mochel
2003-06-12 23:40 ` Paul Mackerras
2003-06-12 23:50 ` Robert Love
2003-06-13 12:44 ` Richard B. Johnson
2003-06-13 12:54 ` Olivier Galibert
2003-06-12 23:52 ` Patrick Mochel
2003-06-13 8:41 ` Alan Cox
2003-06-13 11:00 ` Paul Mackerras
2003-06-13 11:07 ` Herbert Xu
2003-06-13 13:31 ` Alan Cox
2003-06-13 19:57 ` Joe Korty
2003-06-13 21:10 ` Alan Cox
2003-06-13 11:17 ` David Schwartz [this message]
2003-06-13 15:44 ` Davide Libenzi
2003-06-12 23:42 ` Robert Love
2003-06-12 23:45 ` Davide Libenzi
2003-06-12 23:05 ` Robert Love
2003-06-19 19:51 ` Werner Almesberger
2003-06-26 12:17 ` Tommi Virtanen
2003-06-26 14:35 ` Werner Almesberger
2003-06-13 8:40 ` Alan Cox
2003-06-13 9:14 ` Olivier Galibert
2003-06-19 20:53 ` Werner Almesberger
2003-06-13 16:05 ` Steven Dake
2003-06-13 16:32 ` Greg KH
2003-06-13 15:51 ` Steven Dake
2003-06-13 16:41 ` Patrick Mochel
2003-06-13 16:42 ` Greg KH
2003-06-13 17:17 ` Chris Friesen
2003-06-12 22:27 ` Oliver Neukum
2003-06-13 16:03 ` Steven Dake
2003-06-13 16:50 ` Patrick Mochel
2003-06-13 17:10 ` Steven Dake
2003-06-13 18:26 ` Greg KH
2003-06-13 19:02 ` Patrick Mansfield
2003-06-13 17:32 ` Oliver Neukum
2003-06-13 18:23 ` Greg KH
2003-06-13 18:24 ` Greg KH
2003-06-13 7:17 ` Christoph Hellwig
2003-06-13 18:06 ` Linus Torvalds
2003-06-19 23:32 ` Werner Almesberger
2003-06-19 23:42 ` Steven Dake
2003-06-20 0:05 ` Linus Torvalds
2003-06-20 0:10 ` Steven Dake
2003-06-20 0:43 ` Linus Torvalds
2003-06-20 2:26 ` Werner Almesberger
2003-06-20 17:03 ` Steven Dake
2003-06-20 17:18 ` Patrick Mochel
2003-06-14 6:36 John Bradford
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=MDEHLPKNGKAHNMBLJOLKCEFJDKAA.davids@webmaster.com \
--to=davids@webmaster.com \
--cc=linux-kernel@vger.kernel.org \
--cc=paulus@samba.org \
/path/to/YOUR_REPLY
https://kernel.org/pub/software/scm/git/docs/git-send-email.html
* If your mail client supports setting the In-Reply-To header
via mailto: links, try the mailto: link
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;
as well as URLs for NNTP newsgroup(s).