-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA1 On Tue, May 08, 2007 at 08:51:22AM +0530, pradeep singh wrote: > On 5/7/07, Erik Mouw <mouw@xxxxxxxxxxxx> wrote: > >On Mon, May 07, 2007 at 09:25:02PM +0530, Linux Learner wrote: > >> Does -O2 affect SMP safeness of above code? > > > >They're not safe with any optimisation level because the compiler is > >free to reorder instructions around your own lock. Use the kernel > >supplied locking primitives. > > Eric, but the lock primitive acts as a memory barrier , isn't it? For the CPU, yes. But unless you tell the compiler that your inline assembly has certain side effects the compiler can still reorder it with other instructions. > AFAIK gcc still optimises the code even if it encounters a volatile > after asm but that may be the case when gcc is absolutely sure that > the code inside is unreachable. Isn't it? Volatile isn't enough, you really need to tell the compiler the instruction affects memory. > Will this optimization effect the memory barrier act of the lock prefix > here? A lock prefix doesn't automatically tell the compiler there is a memory barrier. Again, just use the kernel supplied functions (atomic_inc() and atomic_dec() in your particular case). First of all the functions are portable among architectures, second they will automatically be relaxed (or even optimised away) in the non-SMP case, and third they are well tested and debugged. Erik - -- They're all fools. Don't worry. Darwin may be slow, but he'll eventually get them. -- Matthew Lammers in alt.sysadmin.recovery -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (GNU/Linux) iD8DBQFGQFzZ/PlVHJtIto0RAi/FAJ9ylZ/LG3P7FH6Q3WA4mlIuVJEhaQCZAUSY qQR5aTQcw62VPHjBtEP1oRM= =oVn1 -----END PGP SIGNATURE----- -- To unsubscribe from this list: send an email with "unsubscribe kernelnewbies" to ecartis@xxxxxxxxxxxx Please read the FAQ at http://kernelnewbies.org/FAQ
