From: Andi Kleen <ak@muc.de>
To: Zachary Amsden <zach@vmware.com>
Cc: Linus Torvalds <torvalds@osdl.org>,
Rusty Russell <rusty@rustcorp.com.au>,
Jeremy Fitzhardinge <jeremy@goop.org>,
Chris Wright <chrisw@sous-sol.org>, Dan Hecht <dhecht@vmware.com>,
Dan Arai <arai@vmware.com>, Andrew Morton <akpm@osdl.org>,
Virtualization Mailing List <virtualization@lists.osdl.org>,
Linux Kernel Mailing List <linux-kernel@vger.kernel.org>,
Daniel Walker <dwalker@mvista.com>
Subject: Re: [PATCH 2/9] Sched clock paravirt op fix.patch
Date: 13 Mar 2007 15:01:29 +0100
Date: Tue, 13 Mar 2007 15:01:29 +0100 [thread overview]
Message-ID: <20070313140129.GB92373@muc.de> (raw)
In-Reply-To: <200703020254.l222sOaM009656@zach-dev.vmware.com>
On Thu, Mar 01, 2007 at 06:54:24PM -0800, Zachary Amsden wrote:
> The custom_sched_clock hook is broken. The result from sched_clock needs to be
> in nanoseconds, not in CPU cycles. The TSC is insufficient for this purpose,
> because TSC is poorly defined in a virtual environment, and mostly represents
> real world time instead of scheduled process time (which can be interrupted
> without notice when a virtual machine is descheduled).
>
> To make the scheduler consistent, we must expose a different nature of time,
> that is scheduled time. So deprecate this custom_sched_clock hack and turn it
> into a paravirt-op, as it should have been all along. This allows the tsc.c
> code which converts cycles to nanoseconds to be shared by all paravirt-ops
> backends.
>
> It is unfortunate to add a new paravirt-op, but this is a very distinct
> abstraction which is clearly different for all virtual machine implementations,
> and it gets rid of an ugly indirect function which I ashamedly admit I hacked
> in to try to get this to work earlier, and then even got in the wrong units.
>
> Please apply.
I think it's better to remove this completely and not allow paravirt
to hook into sched_clock. After all a hypervisor stealing time is no
different from interrupts stealing time and we don't try to handle
that either.
I will remove the custom hook.
-Andi
next prev parent reply other threads:[~2007-03-13 14:01 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2007-03-02 2:54 [PATCH 2/9] Sched clock paravirt op fix.patch Zachary Amsden
2007-03-13 14:01 ` Andi Kleen [this message]
2007-03-13 15:26 ` Jeremy Fitzhardinge
2007-03-13 16:07 ` Chris Wright
2007-03-13 16:16 ` Andi Kleen
2007-03-13 16:37 ` Rik van Riel
2007-03-13 20:56 ` Andi Kleen
2007-03-13 21:05 ` Jeremy Fitzhardinge
2007-03-16 21:29 ` Matt Mackall
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