linux-kernel - Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

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Message-ID: <4B545CE5.6090506@redhat.com>
Date:	Mon, 18 Jan 2010 15:06:45 +0200
From:	Avi Kivity <avi@...hat.com>
To:	Pekka Enberg <penberg@...helsinki.fi>
CC:	Srikar Dronamraju <srikar@...ux.vnet.ibm.com>,
	Peter Zijlstra <peterz@...radead.org>, ananth@...ibm.com,
	Jim Keniston <jkenisto@...ibm.com>,
	Ingo Molnar <mingo@...e.hu>,
	Arnaldo Carvalho de Melo <acme@...radead.org>,
	utrace-devel <utrace-devel@...hat.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Masami Hiramatsu <mhiramat@...hat.com>,
	Maneesh Soni <maneesh@...ibm.com>,
	Mark Wielaard <mjw@...hat.com>,
	LKML <linux-kernel@...r.kernel.org>
Subject: Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)

On 01/18/2010 02:57 PM, Pekka Enberg wrote:
> On 01/18/2010 02:51 PM, Pekka Enberg wrote:
>>> And how many probes do we expected to be live at the same time in
>>> real-world scenarios? I guess Avi's "one million" is more than enough?
>
> Avi Kivity kirjoitti:
>> I don't think a user will ever come close to a million, but we can 
>> expect some inflation from inlined functions (I don't know if uprobes 
>> replicates such probes, but if it doesn't, it should).
>
> Right. I guess we're looking at few megabytes of the address space for 
> normal scenarios which doesn't seem too excessive.
>
> However, as Peter pointed out, the bigger problem is that now we're 
> opening the door for other features to steal chunks of the address 
> space. And I think it's a legitimate worry that it's going to cause 
> problems for 32-bit in the future.
>
> I don't like the idea but if the performance benefits are real (are 
> they?), maybe it's a worthwhile trade-off. Dunno.

If uprobes can trace to buffer memory in the process address space, I 
think the win can be dramatic.  Incidentally it will require injecting 
even more vmas into a process.

Basically it means very low cost tracing, like the kernel tracers.

-- 
error compiling committee.c: too many arguments to function

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