On Wed, 31 Aug 2005, Andi Kleen wrote: > Also with the inline the test should be essentially a single test of > a global variable and jump. Hardly a big performance issue, no?
There are multiple effects of this code. - Additional cacheline in use in the page fault handler increasing the cache foot print. - There are registers in use for checking the global variable. - The compilers will reserve registers for the code that is never executed which may affect other elements of performance. From the register perspective a function call may be better on ia64. Certainly not a big effect (if we make sure the compiler knows that this test mostly fails and insure that the variable is in __mostly_read) but this is a frequently executed code path and the code is there without purpose if CONFIG_KPROBES is off. It wont get too bad unless lots of other people have similar ideas about fixing their race conditions using similar methods. But we will be setting a bad precedent if we allow this. - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to [EMAIL PROTECTED] More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
