[libvirt] [PATCH 2/3] qemu_driver: clamp value for setting sched cpu_shares with --config.

[Eric Blake]

On 05/15/2014 03:39 AM, Dongsheng Yang wrote:
> As shown in 'man virsh' about schedinfo:
> 
>            Note: The cpu_shares parameter has a valid value range of 0-262144;

This note documents historical kernel limits; if the kernel has changed,
this may be out of date.


> Because when we set the value of cpu_shares, when flag is --live,
> write the value into cgroup/cpu.shares. Then it will convert the
> value into the range of [2, 262144]. When flag is --config, we
> set the value into vmdef immidiately and 0 means no settting for

s/immidiately/immediately/
s/settting/setting/

> cpu_shares. When we start vm again, libvirt use default value(1024)

s/use/uses/

> for it.
> 
> This patch clamp the cpu_shares value when flag is --config, then

s/clamp/clamps/

> we will get then "correct" settting in output of virsh schedinfo

s/settting/setting/

> and value in cgroup after next booting of vm.
> 

> +++ b/src/qemu/qemu_driver.c
> @@ -112,6 +112,8 @@ VIR_LOG_INIT("qemu.qemu_driver");
>  #define QEMU_SCHED_MAX_PERIOD           1000000LL
>  #define QEMU_SCHED_MIN_QUOTA               1000LL
>  #define QEMU_SCHED_MAX_QUOTA  18446744073709551LL
> +#define QEMU_SCHED_MIN_SHARES                 2LL
> +#define QEMU_SCHED_MAX_SHARES            262144LL

I'm a bit reluctant to add these numbers - if the kernel ever changes
its range again (which HAS happened for some cgroup tunables), then we
are needlessly preventing use of the newer range.

-- 
Eric Blake   eblake redhat com    +1-919-301-3266
Libvirt virtualization library http://libvirt.org

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