[Barrelfish-users] About CPU performance

tomsun.0.7 tomsun.0.7 at gmail.com
Sat Feb 7 04:02:18 CET 2015

I don't actually care about the measure of CPU speed, I want to know why
Barrelfish performs worse on bare-metal than on QEMU with KVM.

As my second reply demonstrated, I got worse performance while running
applications on bare-metal than both QEMU with KVM and native Linux.

I made sure that it doesn't result from CPU frequency, because I accessed
the hardware performance registers directly within kernel and found it did
run with full speed.

Now, I'm suspecting that is it possible that the performance is influenced
by some other factors like, device interrupts?
Have you ever measured the performance of Barrelfish and compared it with
Linux or other operating system?

On Sat, Feb 7, 2015 at 3:47 AM, Simon Peter <speter at inf.ethz.ch> wrote:

>  I'm also suspecting that it might just be jittery CPU emulation speed
> that's getting you different results. Barrelfish's usleep ultimately uses
> sys_debug_get_tsc_per_ms, so your 2 ways might actually be the same.
> Barrelfish measures CPU speed at bootup, but it's very bad at figuring it
> out correctly on QEMU. I'm not sure what the best way is to get accurate
> results on QEMU.
> On 15-02-04 09:46 PM, tomsun.0.7 wrote:
> Hi,
>  I started a network application who is dedicated to produce packets all
> the time. However, when I started it on bare-metal, I found the throughput
> is only a half of running in QEMU (of course, with KVM enabled).
>  This application is only CPU-intensive, it just produces a lot of
> packets and then destroys them. So it's none of the devices' business. At
> first, I think it results from the low frequency of cores, so I measured
> this by two ways: 1. invoking native Barrelfish interface,
> sys_debug_get_tsc_per_ms, directly; 2. reading tsc and sleeping for 1
> second using POSIX sleep (which is implemented by invoking Barrelfish's
> usleep as I know). However, I got the full-speed results under both
> conditions.
>  So, I don't know whether it results from incorrect measure of frequency
> or some other CPU problems because I even tried to start it with PXE in
> QEMU, and got full performance.
>  What can I do to get normal performance on bare-metal? Or, if it results
> from low frequency of CPUs, what can I do to tune up the frequency?
>  Tom
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