linux-kernel - Interesting interaction between lguest and CFS

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Message-ID: <20070604173710.GR11166@waste.org>
Date:	Mon, 4 Jun 2007 12:37:10 -0500
From:	Matt Mackall <mpm@...enic.com>
To:	Ingo Molnar <mingo@...e.hu>, Rusty Russell <rusty@...tcorp.com.au>,
	akpm@...ux-foundation.org
Cc:	Linux-kernel@...r.kernel.org
Subject: Interesting interaction between lguest and CFS

With 2.6.22-rc3-mm1, I've got a long-running video transcoding going
on. In other windows, I'm compiling, reading email, etc. with no
noticeable problems.

If I fire up lguest and leave it sitting at a shell prompt for a
couple moments, when I return to type something at the prompt, it can
take 2-3 seconds for my input to echo. Once it starts responding,
typing latency disappears. Suspend the other app and the latency
disappears.

The system isn't swapping and has basically no I/O load.

Ok, my transcoding just finished as I was writing this. So I've
reproduced the problem with this Python script that I had handy:

memload.py:
#!/usr/bin/python
a = "a" * 16 * 1024 * 1024
while 1:
    b = a[1:] + "b"
    a = b[1:] + "c"

-- 
Mathematics is the supreme nostalgia of our time.
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