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

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Message-ID: <4B545ACF.40203@cs.helsinki.fi>
Date:	Mon, 18 Jan 2010 14:57:51 +0200
From:	Pekka Enberg <penberg@...helsinki.fi>
To:	Avi Kivity <avi@...hat.com>
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 02:51 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.

			Pekka
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