-----Original Message-----
From: linuxppc-embedded-bounces+leoli=3Dfreescale.com@ozlabs.org
[mailto:linuxppc-embedded-bounces+leoli=3Dfreescale.com@ozlabs.org] On

Behalf Of

Xupei Liang
Sent: Tuesday, August 29, 2006 8:44 AM
To: linuxppc-embedded@ozlabs.org
Subject: RE: atomic operations in user space
=20
I think it is less expensive using atomic operation
sometimes in the user space, e.g. when updating a

Atomic operations are working under strict restrictions.  Generally they
won't work for user space.  Your best bet is to use semaphore instead.

counter. If this counter is to be updated by a lot of
processes, using semaphore can potentially cause a lot
of task switching.
=20
Regards,
=20
Terry Liang
=20
=20

quoted

-----Original Message-----
From: Brent Cook [mailto:bcook at bpointsys.com]
Sent: Thursday, August 24, 2006 10:18 PM
To: linuxppc-embedded at ozlabs.org
Cc: Li Yang-r58472; Terry Liang
Subject: Re: atomic operations in user space

On Thursday 24 August 2006 05:39, Li Yang-r58472

wrote:

quoted

quoted

Why do you need atomic operations in user land?

IPC will be
sufficient

quoted

quoted

to deal with race conditions between processes.

quoted

quoted

Best Regards,

quoted

Leo

What about multiple threads within a process

updating a counter?
=20
Is there anything preventing semaphore to be used in
threads?

quoted

Of course, if you look at these functions in the

kernel header,
they're just 2 or

quoted

3 inline assembly calls - you could easily rewrite

them. Google for
'PowerPC atomic

quoted

increment' and grab one of the unencumbered

implementations if you
need to use it

quoted

in a non-GPL program.

On the other hand, I see no license at the top of my

/usr/include/asm-i386/atomic.h

quoted

file at all, same for PowerPC - are Linux header

files actually GPL or
are they

quoted

more like the glibc headers, with exceptions made

for userspace
programs?

quoted

The atomic operations on x86 were accidentally

exported early on, so
they have to

quoted

hang around apparently for compatibility (there are

some mailing list
threads out

quoted

there to this effect.) Currently, you just have to

assume in Linux
that if you

quoted

include something from /usr/include/linux or asm

that it will not
necessarily be

quoted

cross-version or cross-architecture compatible. Not

every arch in
Linux even has

quoted

atomic operations of this nature, which I guess is

the main reason why
they are

quoted

not exported in general.

- Brent

=20
=20
=20
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