I would assume that would be domU territory, unless somebody can provide any other means
to gather that information.
If your system is reliable and you haven’t
had any wall clock issues in your domains, it *should* be accurate, however I cannot confirm this (I’m
not even sure how I would). There
were various wall clock problems (read: time went backwards, fast clocks, etc)
in domains in 3.0.x under certain conditions, I believe that these have been
fixed in 3.1/3.2 xen releases (some patches for clock
issues were submitted, and no recent bug reports I have found).
Also, independent wallclock
might (this is tentative, I’m not sure if domU
clocks are generated on timer interrupts or when the domU
resumes, the former would be fine, the later would be bad) introduce it’s
own odd skew with heavily loaded systems due to the irregular scheduling and
updating of the domU clocks. Leaving the default behaviour for clock synch should be considered best
practice in this case (and most cases for that matter).
So in short, for
>3.0.x, with independent wallclock disabled
(default behaviour), yes.
>3.0.x, with independent wallclock
enabled, maybe.
3.0.x, likely not on smp,
maybe not regardless.
From:
ridleys@xxxxxxxxx [mailto:ridleys@xxxxxxxxx] On
Behalf Of Edoardo Ceccarelli
Sent: April 13, 2008 2:37 PM
To: [STD]Ein
Cc: xen-users@xxxxxxxxxxxxxxxxxxx
Subject: Re: [Xen-users] SAR in
dom0 or domU
The abstraction that Xen
gives should be enough to give reliable values in certain conditions, I was
wondering about disk troughput for example:
using LVM the dom0 sar shouldn't even be able to produce values cause it cannot
mount the partition
on the other hand the xenU domain should give pretty reliable values... has
anybody tried to compare sar results on xen?
...about cpu's, I completely agree with you
On Sun, Apr 13, 2008 at 5:38 PM, [STD]Ein <ein@xxxxxxxxxxxxxx> wrote:
It depends on what information you are trying to obtain.
If you want information about real hardware (cpu usage, nic's
in dom0 etc) installing in dom0 would be the best case. Installing in
domU can give you good info about individual domain specific memory, network,
tty usage etc, but cpu percentages may be quite artificial, and you wouldn't be
able to see real hardware bottlenecks without examining the other domains.
Hello,
I was wondering about sar under xen: is it more logical to install it on dom0
or in each domU?
about disk i/o it should be able to give disk throughputs even in a dom0, and
maybe, also about cpu usage, memory, etc.
certanly installing sar in a domU will give those values, but will this be
reliable?
what's your opinion about this?
--
Edoardo
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