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Re: [Qemu-devel] QEMU/MIPS & dyntick kernel

To: qemu-devel@nongnu.org
Subject: Re: [Qemu-devel] QEMU/MIPS & dyntick kernel
From: Avi Kivity <avi@qumranet.com>
Date: Tue, 02 Oct 2007 22:27:07 +0200
Cc: linux-mips@linux-mips.org
In-reply-to: <20071002200644.GA19140@hall.aurel32.net>
Original-recipient: rfc822;linux-mips@linux-mips.org
References: <20071002200644.GA19140@hall.aurel32.net>
Sender: linux-mips-bounce@linux-mips.org
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Aurelien Jarno wrote:
Hi,

As announced by Ralf Baechle, dyntick is now available on MIPS. I gave a
try on QEMU/MIPS, and unfortunately it doesn't work correctly.

In some cases the kernel schedules an event very near in the future, which means the timer is scheduled a few cycles only from its current
value. Unfortunately under QEMU, the timer runs too fast compared to the
speed at which instructions are execution.

Sounds like a kernel bug. Can't there conceivably exist real hardware (or a real timeout) that exhibits the same timing?

Especially today with variable clock frequencies, I don't see how the kernel can rely on exact timing.

--
Any sufficiently difficult bug is indistinguishable from a feature.


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