Messages in this thread | | | Date | Sun, 8 Oct 2006 12:31:24 -0700 (PDT) | From | dean gaudet <> | Subject | Re: Performance analysis of Linux Kernel Markers 0.20 for 2.6.17 |
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On Sat, 30 Sep 2006, Mathieu Desnoyers wrote:
> - Optimized > > static int my_open(struct inode *inode, struct file *file) > { > 0: 55 push %ebp > 1: 89 e5 mov %esp,%ebp > 3: 83 ec 0c sub $0xc,%esp > MARK(subsys_mark1, "%d %p", 1, NULL); > 6: b0 00 mov $0x0,%al <-- immediate load 0 in al > 8: 84 c0 test %al,%al > a: 75 07 jne 13 <my_open+0x13>
why not replace the mov+test with "xor %eax,%eax" and then change the 0x75 to a 0x74 to change from jne to je when you want to enable the marker?
i.e. disabled:
31 c0 xor %eax,%eax 75 07 jne 13
enabled:
31 c0 xor %eax,%eax 74 07 je 13
it would save 2 bytes, 1 instruction and avoid partial register writes... and still has the nice property that a single byte store into the code is required for enable/disable (which sounds like a great property -- i assume you were deliberately going for that).
i assume there's probably no reason to tie the sequence to eax either -- you could let gcc choose it (or maybe you already do).
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