[tahoe-dev] profiling, part 3 -- server side

[zooko]

Folks:

While my tahoe node was uploading ten files of 1 mebibyte each,  
Brian's tahoe node was acting as a storage server, accepting shares  
from each file and writing them to its disk.  Our two computers were  
connected by my home DSL line, through the Internet, to the Allmydata  
HQ office DSL line, to Brian's computer.  It is an Athlon64 3500+ in  
32-bit mode, and it was running the excellent Linux tool oprofile  
[1], which samples the entire system's behavior.  Afterward, these  
were the stats for which function was in use when the samples were  
taken.

CPU: CPU with timer interrupt, speed 0 MHz (estimated)
Profiling through timer interrupt
samples  %        app name                 symbol name
365733   91.2007  vmlinux                  default_idle
5046      1.2583  libfreetype.so.6.3.16    (no symbols)
2613      0.6516  libgdk_pixbuf-2.0.so.0.1000.13 (no symbols)
2119      0.5284  libart_lgpl_2.so.2.3.19  (no symbols)
1152      0.2873  libglib-2.0.so.0.1400.1  (no symbols)
949       0.2366  Xorg                     (no symbols)
935       0.2332  libgobject-2.0.so.0.1400.1 (no symbols)
890       0.2219  perl                     (no symbols)
771       0.1923  python2.4                PyEval_EvalFrame
681       0.1698  libpixman-1.so.0.9.5     (no symbols)
659       0.1643  emacs22-x                (no symbols)
585       0.1459  libz.so.1.2.3.3          (no symbols)
575       0.1434  libc-2.6.1.so            memcpy
463       0.1155  libc-2.6.1.so            _int_malloc
372       0.0928  libgtk-x11-2.0.so.0.1000.13 (no symbols)
367       0.0915  libmozjs.so              (no symbols)
360       0.0898  librrd.so.2.0.9          (no symbols)
358       0.0893  firefox-bin              (no symbols)
353       0.0880  vmlinux                  fget_light
340       0.0848  python2.4                lookdict_string
337       0.0840  libc-2.6.1.so            strcmp
336       0.0838  radeon_drv.so            (no symbols)
335       0.0835  vmlinux                  acpi_pm_read
330       0.0823  libgdk-x11-2.0.so.0.1000.13 (no symbols)
320       0.0798  libcrypto.so.0.9.8       (no symbols)
309       0.0771  forcedeth                (no symbols)
265       0.0661  vmlinux                  do_select
259       0.0646  libcairo.so.2.11.5       (no symbols)
253       0.0631  vmlinux                  unix_poll
248       0.0618  libX11.so.6.2.0          (no symbols)
238       0.0593  vmlinux                  handle_IRQ_event


Hm, I see that Brian's computer was estimated at 0 MHz and was using  
timer interrupt.  He must have fallen afoul of the issue mentioned in  
the oprofile faq, "Why is OProfile in timer mode on x86?".  I think  
that the consequences of that are two-fold: 1. code which is non- 
interruptible is invisible to the profiler, and 2.  there might be  
more skew in which the code that gets blamed in the profiling results  
is actually the code that ran right after the expensive code.  I'm  
not sure about that.  Anyway, these results are probably reliable  
anyway.

http://oprofile.sourceforge.net/faq/


Anyway, these results show that tahoe acting as a server uses up  
minimal CPU -- probably around 2%, even if some of the libc, libz, or  
vmlinux costs can be attributed to the Tahoe node.


Regards,

Zooko

[1] http://oprofile.sourceforge.net/news/