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

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Message-ID: <526FC0B2.6060206@iki.fi>
Date:	Tue, 29 Oct 2013 16:05:38 +0200
From:	Pekka Enberg <penberg@....fi>
To:	Hemant Kumar <hkshaw@...ux.vnet.ibm.com>
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 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.

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

> 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.

                         Pekka
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