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

Subject: Re: [Qemu-devel] QEMU/MIPS & dyntick kernel
From: Avi Kivity <>
Date: Tue, 02 Oct 2007 22:27:07 +0200
In-reply-to: <>
Original-recipient: rfc822;
References: <>
User-agent: Thunderbird (X11/20070727)
Aurelien Jarno wrote:

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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