lkml.org 
[lkml]   [2007]   [Mar]   [13]   [last100]   RSS Feed
Views: [wrap][no wrap]   [headers]  [forward] 
 
Messages in this thread
/
Date
Date
From
SubjectRe: [PATCH 2/9] Sched clock paravirt op fix.patch
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
-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@vger.kernel.org
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

\
 
 \ /
  Last update: 2007-03-13 15:03    [W:0.097 / U:0.040 seconds]
©2003-2020 Jasper Spaans|hosted at Digital Ocean and TransIP|Read the blog|Advertise on this site