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

[Wei Liu <wei.liu2@xxxxxxxxxx>]

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


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