Messages in this thread | | | Date | Thu, 03 Jan 2008 17:22:30 +0100 | From | Arjan van de Ven <> | Subject | Re: [patch 1/3] move WARN_ON() out of line |
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Ingo Molnar wrote: > * Arjan van de Ven <arjan@linux.intel.com> wrote: > >> +#define WARN_ON(condition) do_warn_on((unsigned long)(condition), __FILE__, \ >> + __LINE__, __FUNCTION__) > > hm. This passes in 4 arguments to do_warn_on(). > > i think we could get away with no arguments (!), by using section > tricks. Firstly, we can get rid of __FUNCTION__ and replace it with a > ksyms lookup - that is fine enough.
I can see that; I'll play with that
> Secondly, we could put __FILE__ and > __LINE__ into a text section and key it up to the return address from > do_warn_on().
the asm generated for this is 2 movl instructions for immediate to register. Doing fancy tricks ... it may well end up bigger and gain nothing. > > the condition code should not be passed in at all i think - it creates > extra function calls to do_warn_on() all the time.
function calls are *CHEAP*.
passing the condition is actually near free (remember we have regparm!), it's likely to be in a register already anyway.
Doing the test inline makes stuff bigger, and also spreads the branch prediction pain around rather than having one nicely predictable place...
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