On Tue, 4 Sep 2001, Ulrich Weigand wrote:
[SNIPPED...]
>
> If these instructions really *need* to be atomic, then reiserfs should
> ensure they are performed on properly aligned data, or else there might
> be subtle bugs even on Intel, because the operations will not actually
> be atomic (even though they don't trap).
>
Regardless of alignment, locked instructions in Intel machines are
atomic. Any "hidden" read/modify/write operations are performed
by the hardware, under the lock, preventing access by any other
CPUs or DMA.
> If you say that reiserfs doesn't really need these operations to be
> atomic because they run under other locks anyway, then they should not
> be using atomic operations in the first place; this will only cause
> unnecessary slowdown even on Intel.
>
Agreed that there are many "atomic_t" types on some drivers, and
"atomic" operations that don't need to be there. Unless a DMA operation
is in progress, anything executing under a spin-lock doesn't need
to be an "atomic" operation to make it, truly, atomic.
Cheers,
Dick Johnson
Penguin : Linux version 2.4.1 on an i686 machine (799.53 BogoMips).
I was going to compile a list of innovations that could be
attributed to Microsoft. Once I realized that Ctrl-Alt-Del
was handled in the BIOS, I found that there aren't any.
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This archive was generated by hypermail 2b29 : Fri Sep 07 2001 - 21:00:25 EST