On Thu, Oct 17, 2002 at 05:32:03PM +0400, Gleb O. Raiko wrote: > Johannes Stezenbach wrote: > > > > On Thu, Oct 17, 2002 at 02:02:35PM +0200, Maciej W. Rozycki wrote: > > > On Thu, 17 Oct 2002, Gleb O. Raiko wrote: > > > > > > > Implement new sysmips then. > > > > > > I'm not sure if that's a good idea. Glibc alone uses test_and_set(), > > > exchange_and_add(), atomic_add() and compare_and_swap(). Do you want a > > > separate syscall for each of these functions? I think the ll/sc emulation > > > may be the best solution after all. At least it's most flexible and not > > > much slower if at all. > > > > Depends on your usage pattern. E.g. we don't run software that uses > > atomicity.h (i.e. no C++ code), but heavily use pthread_mutex_lock() etc. > > The few uses of atomicity.h internal to glibc don't warrant > > any optimizations. So, if the beql-Method would not exist, I would > > consider implementing a new sysmips for compare_and_swap(). > > I didn't look at newer glibc sources (read: greater than 2.0.6), so the > question. Why is the difference between compare_and_swap and > test_and_set so huge that it eats an exception penalty? ;-) It is not. I wrote: ... But with LL/SC glibc can use compare-and-swap which enables a more efficient linux-threads mutex implementation. This is what makes the difference, at least for glibc-2.2.5. Just grep for HAS_COMPARE_AND_SWAP in your linuxthreads sources. Current glibc from CVS (both HEAD an 2.2 branch) doesn't use sysmips anymore, they rely on LL/SC (emulated or not). Regards, Johannes
