Re: [PATCH V4 0/3] xen-netback: switch to NAPI + kthread 1:1 model

[Wei Liu <wei.liu2@citrix.com>]

Any more comments?

Wei.

On Tue, Aug 06, 2013 at 10:06:00AM +0100, Wei Liu wrote:
> This series implements NAPI + kthread 1:1 model for Xen netback.
> 
> This model
>  - provides better scheduling fairness among vifs
>  - is prerequisite for implementing multiqueue for Xen network driver
> 
> The first two patches are ground work for the third patch. First one
> simplifies code in netback, second one can reduce memory footprint if we
> switch to 1:1 model.
> 
> The third patch has the real meat:
>  - make use of NAPI to mitigate interrupt
>  - kthreads are not bound to CPUs any more, so that we can take
>    advantage of backend scheduler and trust it to do the right thing
> 
> Benchmark done on a Dell T3400 workstation with 4 cores, running 4
> DomUs. Netserver running in Dom0. DomUs do netperf to Dom0 with
> following command: /root/netperf -H Dom0 -fm -l120
> 
> IRQs are distributed to 4 cores by hand in the new model, while in the
> old model vifs are automatically distributed to 4 kthreads.
> 
> * New model
> %Cpu0  :  0.5 us, 20.3 sy,  0.0 ni, 28.9 id,  0.0 wa,  0.0 hi, 24.4 si, 25.9 st
> %Cpu1  :  0.5 us, 17.8 sy,  0.0 ni, 28.8 id,  0.0 wa,  0.0 hi, 27.7 si, 25.1 st
> %Cpu2  :  0.5 us, 18.8 sy,  0.0 ni, 30.7 id,  0.0 wa,  0.0 hi, 22.9 si, 27.1 st
> %Cpu3  :  0.0 us, 20.1 sy,  0.0 ni, 30.4 id,  0.0 wa,  0.0 hi, 22.7 si, 26.8 st
> Throughputs: 2027.89 2025.95 2018.57 2016.23 aggregated: 8088.64
> 
> * Old model
> %Cpu0  :  0.5 us, 68.8 sy,  0.0 ni, 16.1 id,  0.5 wa,  0.0 hi,  2.8 si, 11.5 st
> %Cpu1  :  0.4 us, 45.1 sy,  0.0 ni, 31.1 id,  0.4 wa,  0.0 hi,  2.1 si, 20.9 st
> %Cpu2  :  0.9 us, 44.8 sy,  0.0 ni, 30.9 id,  0.0 wa,  0.0 hi,  1.3 si, 22.2 st
> %Cpu3  :  0.8 us, 46.4 sy,  0.0 ni, 28.3 id,  1.3 wa,  0.0 hi,  2.1 si, 21.1 st
> Throughputs: 1899.14 2280.43 1963.33 1893.47 aggregated: 8036.37
> 
> We can see that the impact is mainly on CPU usage. The new model moves
> processing from kthread to NAPI (software interrupt).
> 
> Changes since V3:
> * rebase on top of net-next
> * group TX and RX fields in different regions of the structure
> * minor bugfix : use GFP_ATOMIC to avoid sleeping in SI context
> * split functional changes and funcation renames into two patches
> * minor coding style fixes
> 
> Wei Liu (3):
>   xen-netback: remove page tracking facility
>   xen-netback: switch to NAPI + kthread 1:1 model
>   xen-netback: rename functions
> 
>  drivers/net/xen-netback/common.h    |  127 ++++--
>  drivers/net/xen-netback/interface.c |  119 +++--
>  drivers/net/xen-netback/netback.c   |  833 +++++++++++------------------------
>  3 files changed, 406 insertions(+), 673 deletions(-)
> 
> -- 
> 1.7.10.4