[Barrelfish-users] About CPU performance

Simon Peter speter at inf.ethz.ch
Fri Feb 6 20:47:24 CET 2015

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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> Barrelfish-users at lists.inf.ethz.ch
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