linux-kernel - Re: [PATCH -tip 4/5] kprobes/x86: Use text_poke_smp

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Message-ID: <4BE9F952.3060505@redhat.com>
Date:	Tue, 11 May 2010 20:41:54 -0400
From:	Masami Hiramatsu <mhiramat@...hat.com>
To:	Mathieu Desnoyers <mathieu.desnoyers@...icios.com>
CC:	Ingo Molnar <mingo@...e.hu>, lkml <linux-kernel@...r.kernel.org>,
	systemtap <systemtap@...rces.redhat.com>,
	DLE <dle-develop@...ts.sourceforge.net>,
	Ananth N Mavinakayanahalli <ananth@...ibm.com>,
	Jim Keniston <jkenisto@...ibm.com>,
	Jason Baron <jbaron@...hat.com>
Subject: Re: [PATCH -tip 4/5] kprobes/x86: Use text_poke_smp_batch

Mathieu Desnoyers wrote:
> * Masami Hiramatsu (mhiramat@...hat.com) wrote:
>> Use text_poke_smp_batch() in optimization path for reducing
>> the number of stop_machine() issues.
>>
>> Signed-off-by: Masami Hiramatsu <mhiramat@...hat.com>
>> Cc: Ananth N Mavinakayanahalli <ananth@...ibm.com>
>> Cc: Ingo Molnar <mingo@...e.hu>
>> Cc: Jim Keniston <jkenisto@...ibm.com>
>> Cc: Jason Baron <jbaron@...hat.com>
>> Cc: Mathieu Desnoyers <mathieu.desnoyers@...icios.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.
With this patch, it went down to 30ms. (x100 faster :))

Thank you,
-- 
Masami Hiramatsu
e-mail: mhiramat@...hat.com

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