Re: [Xen-devel] [RFC PATCH v3 0/8] xen_cpufreq implementation in kernel

[Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>]

On Thu, 23 Oct 2014, Oleksandr Dmytryshyn wrote:
> Hi to all.
> 
> Next series of patches implements xen-cpufreq driver in kernel.
> 
> Cpufreq core and registered cpufreq governors are located in xen. Dom0 has CPU
> driver which can only change frequency of the physical CPUs. In addition this
> driver can change CPUs regulator voltage. At start time xen-cpufreq driver
> in kernel uploads to Xen information about physical cpus.
> Xen notifies Dom0 kernel using VIRQ_CPUFREQ interrupt. Then xen-cpufreq driver
> in kernel uses XEN_SYSCTL_cpufreq_op operation from HYPERVISOR_sysctl 
> hypercall
> to get some parameters from Xen (frequency, relation and cpu number).
> Then xen-cpufreq changes frequency on physical cpu and uses the same
> XEN_SYSCTL_cpufreq_op operation ti give the result to Xen.

This doesn't seem to be very efficient: many hypercalls for a single
operation. I think it would be best to come up with an interface that
doesn't require so many back and forth. Maybe we could have a shared
struct somewhere in memory for Xen to export information.

BTW we are still waiting for benchmarks :-)


> Next configs should be enabled to use xen-cpufreq driver:
> CONFIG_GENERIC_CPUFREQ_CPU0
> CONFIG_XEN_CPUFREQ
> 
> Changed since v1:
>  * added cpufreq_drv_ops which allows to use more than one high-level
>    cpufreq driver
>  * reworked xen-cpufreq and drivers so the same kernel is able to run
>    on bare metal and within Xen.
> 
> Changed since v2:
>  * used VIRQ_CPUFREQ with number 14 instead of the 13
>  * slightly reworked xen-cpufreq driver
> 
> Oleksandr Dmytryshyn (8):
>   PM / OPP: make cpufreq functions dependent on CONFIG_CPU_FREQ_TABLE
>   xen/arm: implement HYPERVISOR_sysctl
>   xen/arm: implement HYPERVISOR_dom0_op
>   xen/arm: add XEN_SYSCTL_cpufreq_op definition
>   cpufreq: cpufreq-cpu0: change cpus data path in devtree for Dom0
>     kernel
>   cpufreq: introduce cpufreq_drv_ops
>   cpufreq: make cpufreq low-level drivers visible for CPUFREQ_DRV_OPS
>     config
>   xen/arm: cpufreq: add xen-cpufreq driver
> 
>  arch/arm/include/asm/xen/hypercall.h |   2 +
>  arch/arm/include/asm/xen/interface.h |   2 +
>  arch/arm/xen/enlighten.c             |   2 +
>  arch/arm/xen/hypercall.S             |   2 +
>  drivers/Makefile                     |   2 +-
>  drivers/base/power/opp.c             |   4 +-
>  drivers/cpufreq/Kconfig              |  39 +-
>  drivers/cpufreq/Makefile             |   2 +
>  drivers/cpufreq/acpi-cpufreq.c       |   5 +-
>  drivers/cpufreq/cpufreq-cpu0.c       |  10 +-
>  drivers/cpufreq/cpufreq.c            | 116 +++--
>  drivers/cpufreq/cpufreq_drv_ops.c    | 196 ++++++++
>  drivers/cpufreq/cpufreq_drv_ops.h    |  54 +++
>  drivers/cpufreq/cpufreq_governor.c   |   4 +-
>  drivers/cpufreq/xen-cpufreq.c        | 889 
> +++++++++++++++++++++++++++++++++++
>  include/linux/cpufreq.h              |   2 +-
>  include/linux/opp.h                  |   2 +-
>  include/xen/interface/platform.h     |   1 +
>  include/xen/interface/sysctl.h       | 664 ++++++++++++++++++++++++++
>  include/xen/interface/xen.h          |   7 +
>  20 files changed, 1939 insertions(+), 66 deletions(-)
>  create mode 100644 drivers/cpufreq/cpufreq_drv_ops.c
>  create mode 100644 drivers/cpufreq/cpufreq_drv_ops.h
>  create mode 100644 drivers/cpufreq/xen-cpufreq.c
>  create mode 100644 include/xen/interface/sysctl.h
> 
> -- 
> 1.9.1
> 
> 
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> http://lists.xen.org/xen-devel
> 

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