To: Arjan van de Ven <arjan@linux.intel.com>
Cc: =?us-ascii?Q?=3D=3FISO-8859-1=3FQ=3FT=3DF6r=3DF6k=5FEdwin=3F=3D?= 
	<edwintorok@gmail.com>,
       Linux Kernel <linux-kernel@vger.kernel.org>
Subject: Re: [PATCH] LatencyTop: make reason (blk_execute_rq+0x7a/0xd) known
References: <47922B2A.7070709@gmail.com> <479241B0.8010500@linux.intel.com>
From: fche@redhat.com (Frank Ch. Eigler)
Date: Sat, 19 Jan 2008 14:40:11 -0500
In-Reply-To: <479241B0.8010500@linux.intel.com> (Arjan van de Ven's message of "Sat, 19 Jan 2008 10:30:08 -0800")
Message-ID: <y0mir1py57o.fsf@ton.toronto.redhat.com>
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Arjan van de Ven <arjan@linux.intel.com> writes:

> T?r?k Edwin wrote:
>> [...]
>> P.S.: LatencyTop could have a feature to ask for more details on unknown
>> latency reasons, and it would generate a systemtap script itself, that
>> would show the backtraces to help figure out whats going on.
>
> I've considered having an option inside the code itself that would print a
> backtrace for, say, an unknown latency larger than 100msec
> but the code got ugly (the accounting gets done in the scheduler path,
> where you can't printk). [...]

Systemtap does not use printk, and can generate decent backtraces from
the kernel (and into userspace before too long).  (FWIW, it seems to
be only a small stretch to implement tools like *top via systemtap
rather than custom-written kernel code.)

- FChE
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