Roman Zippel <[email protected]> wrote:
>
> Hi,
>
> On Thu, 15 Sep 2005, Nick Piggin wrote:
>
> > Roman: any ideas about what you would prefer? You'll notice
> > atomic_inc_not_zero replaces rcuref_inc_lf, which is used several times
> > in the VFS.
>
> In the larger picture I'm not completely happy with these scalibilty
> patches, as they add extra overhead at the lower end. On a UP system in
> general nothing beats:
>
> spin_lock();
> if (*ptr)
> ptr += 1;
> spin_unlock();
>
> The main problem is here that the atomic functions are used in two basic
> situation:
>
> 1) interrupt synchronization
> 2) multiprocessor synchronization
>
> The atomic functions have to assume both, but on UP systems it often is
> a lot cheaper if they don't have to synchronize with interrupts. So
> replacing a spinlock with a few atomic operations can hurt UP performance.
>
Nope. On uniprocessor systems, atomic_foo() doesn't actually do the
buslocked atomic thing.
#ifdef CONFIG_SMP
#define LOCK "lock ; "
#else
#define LOCK ""
#endif
On x86, at least. Other architectures can do the same thing if they have
an atomic-wrt-IRQs add and sub.
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to [email protected]
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/
[Index of Archives]
[Kernel Newbies]
[Netfilter]
[Bugtraq]
[Photo]
[Gimp]
[Yosemite News]
[MIPS Linux]
[ARM Linux]
[Linux Security]
[Linux RAID]
[Video 4 Linux]
[Linux for the blind]
| |
 |