linux-kernel - Re: [PATCH v4 2/3] Support for perf to probe into SDT markers:

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Message-ID: <52700F66.8080105@linux.vnet.ibm.com>
Date:	Wed, 30 Oct 2013 01:11:26 +0530
From:	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>
To:	Pekka Enberg <penberg@....fi>
CC:	David Ahern <dsahern@...il.com>,
	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	LKML <linux-kernel@...r.kernel.org>,
	Peter Zijlstra <peterz@...radead.org>,
	Oleg Nesterov <oleg@...hat.com>,
	"hegdevasant@...ux.vnet.ibm.com" <hegdevasant@...ux.vnet.ibm.com>,
	Ingo Molnar <mingo@...hat.com>,
	"anton@...hat.com" <anton@...hat.com>,
	"systemtap@...rceware.org" <systemtap@...rceware.org>,
	Namhyung Kim <namhyung@...nel.org>,
	Masami Hiramatsu <masami.hiramatsu.pt@...achi.com>,
	"aravinda@...ux.vnet.ibm.com" <aravinda@...ux.vnet.ibm.com>
Subject: Re: [PATCH v4 2/3] Support for perf to probe into SDT markers:

On 10/29/2013 07:35 PM, Pekka Enberg wrote:
> On 10/29/2013 11:55 AM, Hemant Kumar wrote:
>> 1. Where this cache should be? Keeping it in tracing directory inside 
>> the debugfs
>> directory should seem more feasible. And, shall this cache be shareable?
>
> You can't share all of the cache because otherwise you'll expose 
> details on binaries that not everyone has access to.

Correct, that was one of the reason to be worried. And since, to a 
normal user debugfs is not allowed to be entered, then we can keep that 
inside debugfs/tracing subdirectory.

>
> It might make sense to split the cache into two parts: system markers 
> and user markers and share the former.
>

Ok...

>> 2. perf record is a performance intensive process, can we allow the 
>> delay due to
>> this searching process here?
>
> I think scanning is OK if the user specified a SDT markers but not 
> otherwise.
>
> Perhaps you can use a bloom filter to quickly check if the user passed 
> a SDT marker or not.
>

True, bloom filters may help in this case with a quick check.

-- 
Thanks
Hemant Kumar

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