atomic operations in user space

[Liu Dave-r63238]

> >>> 2) These mutexes are based on futexes which requires atomic 
> >>> operations in userspace. These are available on most 
> architectures.
> > Look at
> >>> the glibc code in
> >>> nptl/sysdeps/unix/sysv/linux/powerpc/lowlevellock.h for instance.
> >>> Use that and your PPC manual to implement your atomic operations.
> >>
> >> No matter semaphore or futex, it uses system calls to kernel.
> 
> There is only a system call if there is congestion - that is 
> the whole idea behind the futex.
> 
> >> And the
> >> true atomic operation is in kernel not user space.
> 
> "True" atomic operations are available in user space on most 
> architectures.
> 
> >> Maybe
> >> it's feasible
> >> for other architectures to do atomic operations directly in user 
> >> space.
> >> IMHO, not for powerpc.
> 
> It is available for PowerPC, but not in POWER and POWER2 
> instructionsets according to 
> http://www.nersc.gov/vendor_docs/ibm/asm/lwarx.htm#idx607
> It is the same in the ARM world: Atomic instructions was introduced in
> ARMv6 I believe. Older ARM processors don't have them.
> 
> >
> > Are you meaning that we didn't do atomic operations directly in user
> > space
> > on powerpc platform ?
> >
> 
> Well, that is not the conclusion I get either when reading 
> the glibc code.
> Try to look at glibc-2.3.5/sysdeps/powerpc/bits/atomic.h.
> 
> This is by the way probably what the original post in this 
> thread wanted 
> in the first place!
> 
> Esben

I totally agree with you and Brant about it. I don't believe we cannot
do the atomic operation in user space on powerpc.

-DAve