Messages in this thread | | | Date | Wed, 13 Feb 2008 14:26:27 -0800 | From | "Paul E. McKenney" <> | Subject | Re: [PATCH 3/4] fib_trie: print statistics for multiple tables |
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On Tue, Feb 12, 2008 at 06:35:21PM -0800, Andrew Morton wrote: > On Tue, 12 Feb 2008 16:50:45 -0800 Stephen Hemminger <shemminger@vyatta.com> wrote: > > > +/** > > + * hlist_for_each_entry_continue_rcu - iterate over rcu hlist after current point > > + * @tpos: the type * to use as a loop cursor. > > + * @pos: the &struct hlist_node to use as a loop cursor. > > + * @member: the name of the hlist_node within the struct. > > + */ > > +#define hlist_for_each_entry_continue_rcu(tpos, pos, member) \ > > + for (pos = (pos)->next; \ > > + rcu_dereference(pos) && ({ prefetch(pos->next); 1;}) && \ > > + ({ tpos = hlist_entry(pos, typeof(*tpos), member); 1;}); \ > > + pos = pos->next) > > Is the compiler allowed to look at a term such as > > ({ prefetch(pos->next); 1;}) > > and, when it is used as a truth value, say "hey, that's always true" and > then elide the call to prefetch()? We've no way of telling because this > remains gcc-specific territory, afaik.
The prefetch() definitions I found are "asm volatile". So, as I understand it, the compiler is not supposed to remove it, just as it would not be permitted to remove something that could have a side effect.
> (cc Paul for rcu stuff)
Given my track record with simple functions of late :-/ I will beat this one up a bit...
Thanx, Paul
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