Re: troubleshooting I/O performance bottleneck

[Emmanuel Dreyfus <manu%netbsd.org@localhost>]

On Tue, Apr 28, 2009 at 11:25:40AM +0200, Manuel Bouyer wrote:
> but systat shows 13MB/s throughput, how can dd see 30-35 MB/s ?
> The only explainantion is that part of the file is cached, and the speed
> reported by dd is wrong.

Sorry, it fluctates a lot, I made my snapshot at the wrong time. Here
is another dd from the dom0. The same operation from the domU won't show
a throughput better than 16 MB/s

Proc:r  d  s  w     Csw    Trp    Sys   Int   Sof    Flt  PAGING  SWAPPING
        1  9       4196   5537    277  2752   253   5435  in  out  in  out
                                                        ops         2
  36.6% Sy   0.0% Us   0.0% Ni  15.8% In  47.5% Id    pages
|    |    |    |    |    |    |    |    |    |    |
==================%%%%%%%%                                        forks
                                                                  fkppw
           memory totals (in kB)          2877 Interrupts         fksvm
          real  virtual     free           100 vcpu0 softclock    pwait
Active   60680    60680     1360            20 vcpu0 softnet    2 relck
All     117100   117100  8001352               vcpu0 xenevt     2 rlkok
                                               vcpu0 xencons      noram
Namei         Sys-cache     Proc-cache      18 ioapic1 pin 0      ndcpy
    Calls     hits    %     hits     %    2551 ioapic0 pin 19     fltcp
       37       37  100                        vcpu0 ioapic0      zfod
                                           181 vcpu0 clock        cow
Disks:   md0   cd0   wd0   wd1 raid0           vcpu0 xenbus    64 fmin
 seeks                                         vcpu0 xbd1.3    85 ftarg
 xfers              1354  1349   680         7 vcpu0 xvif1.0      itarg
 bytes               42M   42M   42M           vcpu0 xbd2.3  3774 wired
 %busy              80.2  58.4  98.0           vcpu0 xvif2.0 11081 pdfre
                                               vcpu0 xbd3.3


-- 
Emmanuel Dreyfus
manu%netbsd.org@localhost