From mboxrd@z Thu Jan 1 00:00:00 1970 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. In-Reply-To: <200508310138.09841.ak@suse.de> Message-ID: References: <200508310138.09841.ak@suse.de> MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII Sender: owner-linux-mm@kvack.org Return-Path: To: Andi Kleen Cc: "Luck, Tony" , Rusty Lynch , "Lynch, Rusty" , linux-mm@kvack.org, prasanna@in.ibm.com, linux-ia64@vger.kernel.org, linux-kernel@vger.kernel.org, "Keshavamurthy, Anil S" List-ID: 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, send a message with 'unsubscribe linux-mm' in the body to majordomo@kvack.org. For more info on Linux MM, see: http://www.linux-mm.org/ . Don't email: email@kvack.org