Messages in this thread Patch in this message | | | Date | Sat, 16 Sep 2006 22:29:39 +0200 | From | Ingo Molnar <> | Subject | [patch] kprobes: optimize branch placement |
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* Ingo Molnar <mingo@elte.hu> wrote:
> * Ingo Molnar <mingo@elte.hu> wrote: > > > and have measured the overhead of an unmodified, kprobes-probed and > > djprobes-probed sys_getpid() system-call: > > > > sys_getpid() unmodified latency: 317 cycles [ 0.146 usecs ] > > sys_getpid() kprobes latency: 815 cycles [ 0.377 usecs ] > > sys_getpid() djprobes latency: 380 cycles [ 0.176 usecs ] > > i have taken a look at the kprobes fastpath, and there are a few things > we can do to speed it up. The patch below shaves off 75 cycles from the > kprobes overhead: > > sys_getpid() kprobes-speedup: 740 cycles [ 0.342 usecs ] > > that reduces the kprobes overhead to 423 cycles.
the patch below brings the overhead down to 420 cycles:
sys_getpid() kprobes-speedup: 737 cycles [ 0.341 usecs ]
Ingo
----------> Subject: [patch] kprobes: optimize branch placement From: Ingo Molnar <mingo@elte.hu>
optimize gcc's code generation by hinting branch probabilities.
Signed-off-by: Ingo Molnar <mingo@elte.hu> --- arch/i386/kernel/kprobes.c | 2 +- arch/i386/kernel/traps.c | 2 +- 2 files changed, 2 insertions(+), 2 deletions(-)
Index: linux/arch/i386/kernel/kprobes.c =================================================================== --- linux.orig/arch/i386/kernel/kprobes.c +++ linux/arch/i386/kernel/kprobes.c @@ -220,7 +220,7 @@ int __kprobes kprobe_handler(struct pt_r kcb = get_kprobe_ctlblk(); /* Check we're not actually recursing */ - if (kprobe_running()) { + if (unlikely(kprobe_running())) { p = get_kprobe(addr); if (p) { if (kcb->kprobe_status == KPROBE_HIT_SS && Index: linux/arch/i386/kernel/traps.c =================================================================== --- linux.orig/arch/i386/kernel/traps.c +++ linux/arch/i386/kernel/traps.c @@ -806,7 +806,7 @@ fastcall void __kprobes do_int3(struct p * kernel-mode INT3s are likely kprobes: */ if (!user_mode(regs)) { - if (kprobe_handler(regs)) + if (likely(kprobe_handler(regs))) return; /* This is an interrupt gate, because kprobes wants interrupts disabled. Normal trap handlers don't. */ - 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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