From: Ingo Molnar <mingo@elte.hu>
To: Peter Oberparleiter <oberpar@linux.vnet.ibm.com>
Cc: Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Andrew Morton <akpm@linux-foundation.org>,
Linus Torvalds <torvalds@linux-foundation.org>
Subject: Re: gcov: enable GCOV_PROFILE_ALL for x86_64
Date: Mon, 22 Jun 2009 12:56:09 +0200 [thread overview]
Message-ID: <20090622105609.GA17456@elte.hu> (raw)
In-Reply-To: <4A3F6AD5.1030703@linux.vnet.ibm.com>
Another thing i was thinking about:
the GCOV code cannot be enabled in distros right now, due to the
high compiler-generated overhead, and due to the fact that the gcov
data structures used are single threaded. (which makes a gcov
enabled kernel very slow on SMP, due to the global cacheline
bounces)
IMO it would be _much_ better to implement hardware-assisted
call-graph tracking:
- Use the BTS (Branch Trace Store) facilities to hardware-sample
all branches+calls (optionally, dynamically enable-able)
- Post-process the raw branch trace information (in the kernel
BTS-overflow irq handler) to calculate call-coverage information.
Unlike the unconditional GCC based GCOV stuff that is currently
upstream, BTS tracing is supported by a large range of hardware and
it can be enabled _transparently_, so it could be built in and
enabled by distros too, to test code coverage.
Would you be interested in looking at (and implementing) this?
Thanks,
Ingo
next prev parent reply other threads:[~2009-06-22 10:56 UTC|newest]
Thread overview: 4+ messages / expand[flat|nested] mbox.gz Atom feed top
[not found] <200906182200.n5IM0jFq007278@hera.kernel.org>
2009-06-20 10:14 ` gcov: enable GCOV_PROFILE_ALL for x86_64 Ingo Molnar
2009-06-22 11:28 ` Peter Oberparleiter
2009-06-22 10:56 ` Ingo Molnar [this message]
2009-06-23 7:42 ` Peter Oberparleiter
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