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

[Paolo Bonzini]

On 10/27/2014 03:13 PM, Alexandre DERUMIER wrote:
>>> 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.

You are missing debug information unfortunately, but the slowdown seems
to be related to futexes.

Paolo