Messages in this thread |  | | | Date | Wed, 12 May 2010 11:27:47 -0400 | | From | Mathieu Desnoyers <> | | Subject | Re: [PATCH -tip 4/5] kprobes/x86: Use text_poke_smp_batch |
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* Masami Hiramatsu (mhiramat@redhat.com) wrote: > Mathieu Desnoyers wrote: > > * Masami Hiramatsu (mhiramat@redhat.com) wrote: > >> Use text_poke_smp_batch() in optimization path for reducing > >> the number of stop_machine() issues. > >> > >> Signed-off-by: Masami Hiramatsu <mhiramat@redhat.com> > >> Cc: Ananth N Mavinakayanahalli <ananth@in.ibm.com> > >> Cc: Ingo Molnar <mingo@elte.hu> > >> Cc: Jim Keniston <jkenisto@us.ibm.com> > >> Cc: Jason Baron <jbaron@redhat.com> > >> Cc: Mathieu Desnoyers <mathieu.desnoyers@efficios.com> > >> --- > >> > >> arch/x86/kernel/kprobes.c | 37 ++++++++++++++++++++++++++++++------- > >> include/linux/kprobes.h | 2 +- > >> kernel/kprobes.c | 13 +------------ > >> 3 files changed, 32 insertions(+), 20 deletions(-) > >> > >> diff --git a/arch/x86/kernel/kprobes.c b/arch/x86/kernel/kprobes.c > >> index 345a4b1..63a5c24 100644 > >> --- a/arch/x86/kernel/kprobes.c > >> +++ b/arch/x86/kernel/kprobes.c > >> @@ -1385,10 +1385,14 @@ int __kprobes arch_prepare_optimized_kprobe(struct optimized_kprobe *op) > >> return 0; > >> } > >> > >> -/* Replace a breakpoint (int3) with a relative jump. */ > >> -int __kprobes arch_optimize_kprobe(struct optimized_kprobe *op) > >> +#define MAX_OPTIMIZE_PROBES 256 > > > > So what kind of interrupt latency does a 256-probes batch generate on the > > system ? Are we talking about a few milliseconds, a few seconds ? > > From my experiment on kvm/4cpu, it took about 3 seconds in average.
That's 3 seconds for multiple calls to stop_machine(). So we can expect latencies in the area of few microseconds for each call, right ?
> With this patch, it went down to 30ms. (x100 faster :))
This is beefing up the latency from few microseconds to 30ms. It sounds like a regression rather than a gain to me.
Thanks,
Mathieu
> > Thank you, > -- > Masami Hiramatsu > e-mail: mhiramat@redhat.com >
-- Mathieu Desnoyers Operating System Efficiency R&D Consultant EfficiOS Inc. http://www.efficios.com
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