[kvm-ppc-devel] Oprofile kvmppc - mini howto and restrictions (atm)

[Christian Ehrhardt <ehrhardt@linux.vnet.ibm.com>]

to sample you can use:
opcontrol --vmlinux=/root/vmlinux.host --session-dir=/mnt/usb/oprofile/
# I use that session dir to separate measurements e.g. so you can store several measurements to analyze later on

opcontrol --start	# starts profiling
opcontrol --stop	# stops but not ends profiling
opcontrol --shutdown	# stops profiling and ensures all data is flushed to the samples dir

Example:
bash-3.00# opcontrol --vmlinux=/root/vmlinux.host --session-dir=/mnt/usb/oprofile/
bash-3.00# opcontrol --start
Using 2.6+ OProfile kernel interface.
Reading module info.
Using log file /mnt/usb/oprofile//samples/oprofiled.log
Daemon started.
Profiler running.

### now I start the guest in another window - boot from ramdisk image with virtio-block&net enabled, shutdown when bootet, killed when on halt

bash-3.00# opcontrol --shutdown
Stopping profiling.
Killing daemon.

# you can now use opreport to analyze the date, use --session-dir to specify what you want to analyze.

That way for the start I sampled a boot&halt and in another sample whats still going on when the guest idles 2 minutes at the login prompt
=> Reports in the following mails

### important ###
Note the bad thing, atm oprofile on ppc440 seems not to have hw perf counters available. Therefore it is covered with the fallback timer-interrupt. But this has drawbacks:
=>from the oprfile info page:
"In 2.6 kernels on CPUs without OProfile support for the hardware performance counters, the driver falls back to using the timer interrupt for profiling. Like the RTC mode in 2.4 kernels, this is not able to profile code that has interrupts disabled. Note that there are no configuration parameters for setting this, unlike the RTC and hardware performance counter setup."

So oprofile works but without real cpu perf counters it will be nearly useless, because we have interrupts disabled in most code we want to profile. I need to look out for some beta support (or write my own) for ppc440 cpu perf counters to enable that for us :(

-- 

Grüsse / regards, 
Christian Ehrhardt
IBM Linux Technology Center, Open Virtualization

-------------------------------------------------------------------------
Check out the new SourceForge.net Marketplace.
It's the best place to buy or sell services for
just about anything Open Source.
http://ad.doubleclick.net/clk;164216239;13503038;w?http://sf.net/marketplace
_______________________________________________
kvm-ppc-devel mailing list
kvm-ppc-devel@lists.sourceforge.net
https://lists.sourceforge.net/lists/listinfo/kvm-ppc-devel