Am 08.11.2012 17:06, schrieb Mark Nelson:
On 11/08/2012 09:45 AM, Stefan Priebe - Profihost AG wrote:Am 08.11.2012 16:01, schrieb Sage Weil:On Thu, 8 Nov 2012, Stefan Priebe - Profihost AG wrote:Is there any way to find out why a ceph-osd process takes around 10 times more load on rand 4k writes than on 4k reads?Something like perf or oprofile is probably your best bet. perf can be tedious to deploy, depending on where your kernel is coming from. oprofile seems to be deprecated, although I've had good results with it in the past.I've recorded 10s with perf - it is now a 300MB perf.data file. Sadly i've no idea what todo with it next.Pour yourself a stiff drink! (haha!) Try just doing a "perf report" in the directory where you've got the data file. Here's a nice tutorial: https://perf.wiki.kernel.org/index.php/Tutorial Also, if you see missing symbols you might benefit by chowning the file to root and running perf report as root. If you still see missing symbols, you may want to just give up and try sysprof.
I've now used google perftools / google CPU profiler. It was the only tool who worked out of the box ;-)
Attached is a PDF with a profiled ceph-osd process while 4k random write. Stefan
Attachment:
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