linux-kernel - Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow tracing units

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Message-ID: <20131219103134.GD30183@twins.programming.kicks-ass.net>
Date:	Thu, 19 Dec 2013 11:31:34 +0100
From:	Peter Zijlstra <peterz@...radead.org>
To:	Alexander Shishkin <alexander.shishkin@...ux.intel.com>
Cc:	Arnaldo Carvalho de Melo <acme@...stprotocols.net>,
	Ingo Molnar <mingo@...hat.com>, linux-kernel@...r.kernel.org,
	David Ahern <dsahern@...il.com>,
	Frederic Weisbecker <fweisbec@...il.com>,
	Jiri Olsa <jolsa@...hat.com>, Mike Galbraith <efault@....de>,
	Namhyung Kim <namhyung@...il.com>,
	Paul Mackerras <paulus@...ba.org>,
	Stephane Eranian <eranian@...gle.com>,
	Andi Kleen <ak@...ux.intel.com>
Subject: Re: [PATCH v0 04/71] itrace: Infrastructure for instruction flow
 tracing units

On Thu, Dec 19, 2013 at 09:53:44AM +0200, Alexander Shishkin wrote:
> Yes and some implementations of PT have the same issue, but you can do a
> sufficiently large high order allocation and map it to userspace and
> still no copying (or parsing/decoding) in kernel space required.

What's sufficiently large? The largest we could possibly allocate is
something like 4k^11 which is 8M or so. That's not all that big given
you keep saying it generates in the order of 100 MB/s.

Also, 'some implementations', that sounds like a fail right there. Why
are there already different implementations, and some which such stupid
design, of something this new?

How about just saying NO to the ones that requires physically contiguous
allocations?
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