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Date: Sun, 8 Oct 2006 12:40:29 -0700 (PDT) From: dean gaudet <dean@...tic.org> To: Mathieu Desnoyers <compudj@...stal.dyndns.org> cc: Martin Bligh <mbligh@...gle.com>, "Frank Ch. Eigler" <fche@...hat.com>, Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>, prasanna@...ibm.com, Andrew Morton <akpm@...l.org>, Ingo Molnar <mingo@...e.hu>, Mathieu Desnoyers <mathieu.desnoyers@...ymtl.ca>, Paul Mundt <lethal@...ux-sh.org>, linux-kernel <linux-kernel@...r.kernel.org>, Jes Sorensen <jes@....com>, Tom Zanussi <zanussi@...ibm.com>, Richard J Moore <richardj_moore@...ibm.com>, Michel Dagenais <michel.dagenais@...ymtl.ca>, Christoph Hellwig <hch@...radead.org>, Greg Kroah-Hartman <gregkh@...e.de>, Thomas Gleixner <tglx@...utronix.de>, William Cohen <wcohen@...hat.com>, ltt-dev@...fik.org, systemtap@...rces.redhat.com, Alan Cox <alan@...rguk.ukuu.org.uk>, Jeremy Fitzhardinge <jeremy@...p.org>, Karim Yaghmour <karim@...rsys.com>, Pavel Machek <pavel@...e.cz>, Joe Perches <joe@...ches.com>, "Randy.Dunlap" <rdunlap@...otime.net>, "Jose R. Santos" <jrs@...ibm.com> Subject: Re: Performance analysis of Linux Kernel Markers 0.20 for 2.6.17 On Sun, 8 Oct 2006, dean gaudet wrote: > 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 actually... why even destroy the register... i bet this is the best choice: 39 c0 cmp %eax,%eax 75 07 jne 13 that satisfies the macro-op fusion rules on core2 as well... now you shouldn't even ask gcc for a register you should just hardwire %eax so it doesn't get confused (probably need to tell it "cc" is modified). -dean - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.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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