Re: [Qemu-devel] is it possible to use a disk with multiple iothreads ?

[Alexandre DERUMIER]

>>That's very interesting! Please keep Josh and me in CC when you want to
>>discuss the results.

Here the aggregate results (perf report details attached in this mail)

+  33,02%    3974368751  kvm  [kernel.kallsyms]                                 
                                                                                
                                                                 
+  23,66%    2847206635  kvm  libc-2.13.so                                      
                                                                                
                                                                 
+  18,79%    2262052133  kvm  librados.so.2.0.0                                 
                                                                                
                                                                 
+  11,04%    1328581527  kvm  librbd.so.1.0.0                                   
                                                                                
                                                                 
+   5,87%     706713737  kvm  libpthread-2.13.so                                
                                                                                
                                                                 
+   3,75%     451690142  kvm  kvm                                               
                                                                                
                                                                 
+   2,74%     329457334  kvm  libstdc++.so.6.0.17                               
                                                                                
                                                                 
+   0,51%      61519664  kvm  [vdso]                                            
                                                                                
                                                                             +  
 0,42%      50000089  kvm  libglib-2.0.so.0.3200.4                              
                                                                                
                                                                          +   
0,15%      18119658  kvm  libm-2.13.so                                          
                                                                                
                                                                         +   
0,05%       5705776  kvm  librt-2.13.so                                         
                                                                                
                                                                         +   
0,00%        356625  kvm  libz.so.1.2.7




>> 23,66%    2847206635  kvm  libc-2.13.so
This one is mostly malloc,free,...


I see almost same results using fio with rbdengine on the host (outside the kvm 
process).
So I think they are all mostly related to librbd.



----- Mail original -----

De: "Stefan Hajnoczi" <address@hidden>
À: "Alexandre DERUMIER" <address@hidden>
Cc: "qemu-devel" <address@hidden>, "josh durgin" <address@hidden>
Envoyé: Lundi 27 Octobre 2014 14:19:58
Objet: Re: is it possible to use a disk with multiple iothreads ?

On Fri, Oct 24, 2014 at 03:39:52PM +0200, Alexandre DERUMIER wrote:
> >>Regarding Ceph, do you know why it burns a lot of CPU?
>
> I'm currently doing some perfs to find why is so huge.
>
> One thing is that qemu+ qemu rbd block driver + librbd seem to use 2-3x more 
> cpu, than passing krbd /dev/rbd0 from host to qemu.
> Don't known yet if the problem is librbd or qemu rbd block driver.

That's very interesting! Please keep Josh and me in CC when you want to
discuss the results.

Stefan

report.txt.gz
Description: GNU Zip compressed data