Re: [MirageOS-devel] Profiling Mirage on Xen

[Thomas Leonard <talex5@xxxxxxxxx>]

On 11 August 2014 14:04, David Scott <scott.dj@xxxxxxxxx> wrote:
>
> On Mon, Aug 11, 2014 at 12:32 PM, Thomas Leonard <talex5@xxxxxxxxx> wrote:
>>
>> Has anyone made any tools for profiling on Xen?
>
>
> The closest thing I can think of is xentrace/xenalyse:
>
> http://blog.xen.org/index.php/2012/09/27/tracing-with-xentrace-and-xenalyze/
>
> This will tell you what Xen can see: eg how the vCPUs map to pCPUs and when
> they block on events etc.

Thanks. For now, I've pinned dom0 to CPU 0 and my unikernel to CPU 1.

>> I want to see why my network service on Xen/ARM only gets about 5 MB/s
>> (while a Linux guest gets about 45 MB/s).
>>
>> I tried compiling with profiling on ("true: profile" in the _tags) and
>> wrote a __gnu_mcount_nc function to dump all the results to a buffer
>> [1], plus a script to turn the addresses back into symbols and guess
>> the nesting (a bit unreliable, as it doesn't tell you when the
>> function finishes).
>>
>> Here's an example CSV of the output (the unikernel waits for a TCP
>> connection and then streams data to it as fast as it can):
>>
>>   http://test.roscidus.com/static/sample-output.csv.bz2
>>
>> I haven't checked it carefully to see if it's correct - this is just
>> an example of the kind of output. It shows the call graph and the
>> (cumulative) time spent in each function. Since it doesn't know the
>> end times, it assumes a function runs until one of its parents calls
>> something else.
>
>
> Cool -- it would be great to polish up a tool like this.

Yes, I think there's a lot we could do here. I've written up the
profiling I've done so far here:

http://roscidus.com/blog/blog/2014/08/15/optimising-the-unikernel/

The graphs are quite interesting - if people familiar with the code
could explain what's going on (especially with the block device) that
would be great!

Overall, the changes increased the queuing service's download rate
from 2.46 MB/s to 7.24 MB/s, which is nice but still a bit
disappointing.


-- 
Dr Thomas Leonard        http://0install.net/
GPG: 9242 9807 C985 3C07 44A6  8B9A AE07 8280 59A5 3CC1
GPG: DA98 25AE CAD0 8975 7CDA  BD8E 0713 3F96 CA74 D8BA

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