Re: [PATCH] PPC atomic.h add compare_exchange_val forms

["Kevin B. Hendricks" <kevin dot hendricks at sympatico dot ca>]

Hi,

And one follow up question if possible:

To be completely safe on ppc should all atomic types actually fill the 
entire cache line size of the cpu to prevent two separate atomic types 
from falling into the same cache line.

If two threads ever compete for them neither may ever get the reservation 
clearly without the other one clearing it first and we could end up with 
some sort of strange live-lock situation?

Or am I just being paranoid about ppc synchronization issues!?!

Thanks,

Kevin



On April 15, 2003 12:32 pm, Kevin B. Hendricks wrote:
> Hi,
> 
> Forgive my ignorance here, I am no expert and I am asking mainly to learn 
> things...
> 
> But do we need to worry about a lwarx. and ldarx. setting reservations 
bits 
> (on cache lines representing addresses) that never see paired a stdcx. or 
> a stwcx. to clear them when the jump happens?
> 
> Or does the clear happen in some other way?
> 
> Also do we need to worry about alignment of a 64 bit value in the 32 byte 
> cache line to prevent layouts that might end up having 4 of the bytes in 
> one cache line and the next four in another cache line making the 
> reservation idea not work properly?
> 
> Thanks for any hints.
> 
> Kevin
> 
> 
> 
> 
> On April 15, 2003 11:56 am, Steven Munroe wrote:
> > Changes in nptl/pthreadP.h (introduced __do_cancel which uses
> > THREAD_ATOMIC_BIT_SET) require atomic_compare_and_exchange_val_acq to 
be
> > explicitely implemented for all architectes. PPC32 and PPC64 did not
> > specifically define this form. The attached patch implement
> > atomic_compare_and_exchange_val_acq for 32-bit (both PPC32/PPC64) and 
> 64-bit
> > (PPC64 only).
> > 
> > 2003-04-15  Steven Munroe  <sjmunroe at us dot ibm dot com>
> >         * sysdeps/powerpc/bits/atomic.h 
> > 	[__powerpc64] (__arch_compare_and_exchange_val_64_acq): Define.
> >         [! __powerpc64] (__arch_compare_and_exchange_val_64_acq): 
Defined 
> > 	as abort stub.
> > 	(__arch_compare_and_exchange_val_32_acq): Define.
> > 	(atomic_compare_and_exchange_val_acq): Define.
> > 
> > -- 
> > Steven Munroe
> > sjmunroe at us dot ibm dot com
> > Linux on PowerPC-64 Development
> > GLIBC for PowerPC-64 Development
> 
>