linux-kernel - Re: [patch 2/3] Latencytop instrumentations part 1

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Message-ID: <47913435.4010004@linux.intel.com>
Date:	Fri, 18 Jan 2008 15:20:21 -0800
From:	Arjan van de Ven <arjan@...ux.intel.com>
To:	"Frank Ch. Eigler" <fche@...hat.com>
CC:	Arjan van de Ven <arjan@...radead.org>,
	Linux Kernel Mailing List <linux-kernel@...r.kernel.org>,
	Linus Torvalds <torvalds@...ux-foundation.org>,
	Ingo Molnar <mingo@...e.hu>,
	Andrew Morton <akpm@...ux-foundation.org>
Subject: Re: [patch 2/3] Latencytop instrumentations part 1

Frank Ch. Eigler wrote:
> Hi -
> 
> On Fri, Jan 18, 2008 at 02:33:34PM -0800, Arjan van de Ven wrote:
>> [...]
>>> Can you suggest of some reason why all this instrumentation could
>>> not be in the form of standard markers (perhaps conditionally
>>> compiled out if necessary)?
>> sure. Every instrumentation you see is of the nested kind (since the lowest level
>> of nesting is already automatic via wchan).
>> If markers can provide me the following semantics, I'd be MORE than happy to use markers:
>> [...]
>> If markers can provide that semantics ... you sold me.
> 
> Further to what acme said, markers are semantics-free.  Callback
> functions that implement your entry & exit semantics can be attached
> at run time, at your pleasure.  (So can systemtap probes, for that
> matter.)  The main difference would be that these callback functions
> would have manage the per-thread LIFO data structures themselves,
> instead of allocating backpointers on the kernel stack.  (Bonus marks
> for not modifying task_struct. :-)

modifying task struct to have storage space is no big deal...
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