linux-kernel - Re: [PATCH] LatencyTop: make reason (blk_execute

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Message-ID: <y0mir1py57o.fsf@ton.toronto.redhat.com>
Date:	Sat, 19 Jan 2008 14:40:11 -0500
From:	fche@...hat.com (Frank Ch. Eigler)
To:	Arjan van de Ven <arjan@...ux.intel.com>
Cc:	=?ISO-8859-1?Q?T=F6r=F6k_Edwin?= 
	<edwintorok@...il.com>, Linux Kernel <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH] LatencyTop: make reason (blk_execute_rq+0x7a/0xd) known

Arjan van de Ven <arjan@...ux.intel.com> writes:

> Török 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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