David Howells <David.Howells@nexor.co.uk> schrieb / wrote am / at : 07.09.2000
16:25:29
>
> Hold on a moment... You said "between the test bit and set bit"... this is a
> single CPU instruction! With the lock prefix, there should be no between.
>
> Also, a quote from asm/bitops.h:
> - /*
> - * These have to be done with inline assembly: that way the bit-setting
> - * is guaranteed to be atomic. All bit operations return 0 if the bit
> - * was cleared before the operation and != 0 if it was not.
> - *
> - * bit 0 is the LSB of addr; bit 32 is the LSB of (addr+1).
> - */
>
> Doesn't "atomic" mean SMP safe?
>
> What's the point in the lock prefix if it doesn't make things SMP safe (after
> all, the unadorned instructions are UP safe...)?
The Pentium Processor manual (section 19) explicitly mentions the BTx
instructions together with the LOCK prefix as an SMP save way to access
semaphores.
Bernhard
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
Please read the FAQ at http://www.tux.org/lkml/
This archive was generated by hypermail 2b29 : Thu Sep 07 2000 - 21:00:30 EST