Mailing List Archive

Current time
Hi,

I'm trying to run kernel compilations on a VM and my times are better
than on the host machine. I'm using the time command, so I'm assuming
its bugged. I try to use hwclock, and it spits out nothing. Is there
an easy way to determine REAL time in a virtual machine?

Thanks,
David
RE: Current time [ In reply to ]
> I'm trying to run kernel compilations on a VM and my times
> are better than on the host machine. I'm using the time
> command, so I'm assuming its bugged. I try to use hwclock,
> and it spits out nothing. Is there an easy way to determine
> REAL time in a virtual machine?

The elapsed time reported by 'time' should be accurate. system and user
time may not be entirely correct, as the kernel doesn't really
understand that its not running the whole time.

hwclock won't work as the unprivileged guest isn't authorized to read
directly from the hardware clock. 'date' should work fine.

Ian

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RE: Current time [ In reply to ]
You're right Ian. The timing seems to be correct. I recompiled my Xen
kernel in an attempt to optimize it. There must've been something
enabled that degraded performance on the host but not the VM. The
majority of what I changed was removing unused drivers from modules and
kernels and enabling himem (4GB). Any ideas on that?

Thanks,
David

-----Original Message-----
From: Ian Pratt [mailto:m+Ian.Pratt@cl.cam.ac.uk]
Sent: Tuesday, June 07, 2005 4:04 PM
To: Wolinsky, David; xen-users@lists.xensource.com
Cc: ian.pratt@cl.cam.ac.uk
Subject: RE: [Xen-users] Current time


> I'm trying to run kernel compilations on a VM and my times are better
> than on the host machine. I'm using the time command, so I'm assuming

> its bugged. I try to use hwclock, and it spits out nothing. Is there

> an easy way to determine REAL time in a virtual machine?

The elapsed time reported by 'time' should be accurate. system and user
time may not be entirely correct, as the kernel doesn't really
understand that its not running the whole time.

hwclock won't work as the unprivileged guest isn't authorized to read
directly from the hardware clock. 'date' should work fine.

Ian


_______________________________________________
Xen-users mailing list
Xen-users@lists.xensource.com
http://lists.xensource.com/xen-users
RE: Current time [ In reply to ]
> You're right Ian. The timing seems to be correct. I
> recompiled my Xen kernel in an attempt to optimize it. There
> must've been something enabled that degraded performance on
> the host but not the VM. The majority of what I changed was
> removing unused drivers from modules and kernels and enabling
> himem (4GB). Any ideas on that?

Hmm, I don't know what could have caused that. Enabling highmem 4g only
causes a tiny slowdown, measureable only by microbenchmarks.

Ian

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