Robert White writes:
> This will, hopefully, be my out-comment on this thread.
>
[...]
>
> 4) All locks (spin or otherwise) should obviously be held for the shortest
> amount of time reasonably possible which still produces the correct result.
>
> If this needs explaining... 8-)
It surely does.
Consider two loops:
(1)
spin_lock(&lock);
list_for_each_entry(item, ...) {
do something with item;
}
spin_unlock(&lock);
versus
(2)
list_for_each_entry(item, ...) {
spin_lock(&lock);
do something with item;
spin_unlock(&lock);
}
and suppose they both are equally correct. Now, in (2) total amount of
time &lock is held is smaller than in (1), but (2) will usually perform
worse on SMP, because:
. spin_lock() is an optimization barrier
. taking even un-contended spin lock is an expensive operation, because
of the cache coherency issues.
>
[...]
>
> Rob.
>
Nikita.
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This archive was generated by hypermail 2b29 : Fri May 23 2003 - 22:00:53 EST