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

From:  Pekka Enberg <penberg-AT-cs.helsinki.fi>
To:  Avi Kivity <avi-AT-redhat.com>
Subject:  Re: [RFC] [PATCH 1/7] User Space Breakpoint Assistance Layer (UBP)
Date:  Mon, 18 Jan 2010 14:57:51 +0200
Cc:  Srikar Dronamraju <srikar-AT-linux.vnet.ibm.com>, Peter Zijlstra <peterz-AT-infradead.org>, ananth-AT-in.ibm.com, Jim Keniston <jkenisto-AT-us.ibm.com>, Ingo Molnar <mingo-AT-elte.hu>, Arnaldo Carvalho de Melo <acme-AT-infradead.org>, utrace-devel <utrace-devel-AT-redhat.com>, Frederic Weisbecker <fweisbec-AT-gmail.com>, Masami Hiramatsu <mhiramat-AT-redhat.com>, Maneesh Soni <maneesh-AT-in.ibm.com>, Mark Wielaard <mjw-AT-redhat.com>, LKML <linux-kernel-AT-vger.kernel.org>
Archive-link:  Article, Thread

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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