Messages in this thread | | | Date | Tue, 30 Aug 2005 16:54:56 -0700 (PDT) | From | Christoph Lameter <> | Subject | Re: [PATCH] Only process_die notifier in ia64_do_page_fault if KPROBES is configured. |
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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 majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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