Re: [libvirt] [PATCH 2/3] qemu_driver: clamp value for setting sched cpu_shares with --config.
On 05/15/2014 08:56 PM, Martin Kletzander wrote:
On Thu, May 15, 2014 at 06:39:50PM +0900, Dongsheng Yang wrote:
> As shown in 'man virsh' about schedinfo:
>
> Note: The cpu_shares parameter has a valid value range of
> 0-262144;
> Negative values are wrapped to positive, and larger values are
> capped at
> the maximum. Therefore, -1 is a useful shorthand for 262144.
> On the Linux kernel, the values 0 and 1 are automatically
> converted to
> a minimal value of 2.
> it works well with --live, but not with --config.
>
> Example:
> # virsh schedinfo rhel7-ful --set cpu_shares=0 --config
> Scheduler : posix
> cpu_shares : 0
> vcpu_period : 0
> vcpu_quota : 0
> emulator_period: 0
> emulator_quota : 0
> cpu_shares is 0 rather than expected 2.
>
> What's worse, when we start it again, it is the default value of
> cpu_shares 1024.
>
> 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
> cpu_shares. When we start vm again, libvirt use default value(1024)
> for it.
>
> This patch clamp the cpu_shares value when flag is --config, then
> we will get then "correct" settting in output of virsh schedinfo
> and value in cgroup after next booting of vm.
>
I was under the impression that this was meant to be fixed by commit
97814d8a, what's the difference to that?
Commit 97814d8a is to make the output of virsh schedinfo --live showing
the real value in cgroup.
This patch here is to do another thing, it is about --config. When we
use --live
to set cpu_shares, as shown in "man virsh", we depend on the conversion by
cgroup. But when we set it with --config, we did not actually write the
value
into cgroup, then the value will not be converted to the expected value
in manpage.
And as I described above, when we set cpu_shares=0 with --config, we
will get
1024 in next booting.
Martin
> Signed-off-by: Dongsheng Yang <yangds.fnst(a)cn.fujitsu.com>
> ---
> src/qemu/qemu_driver.c | 6 +++++-
> 1 file changed, 5 insertions(+), 1 deletion(-)
>
> diff --git a/src/qemu/qemu_driver.c b/src/qemu/qemu_driver.c
> index 52ca47c..7648865 100644
> --- a/src/qemu/qemu_driver.c
> +++ 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
>
> #if HAVE_LINUX_KVM_H
> # include <linux/kvm.h>
> @@ -9063,7 +9065,9 @@
> qemuDomainSetSchedulerParametersFlags(virDomainPtr dom,
> }
>
> if (flags & VIR_DOMAIN_AFFECT_CONFIG) {
> - vmdef->cputune.shares = value_ul;
> + vmdef->cputune.shares = CLAMP(value_ul,
> + QEMU_SCHED_MIN_SHARES,
> + QEMU_SCHED_MAX_SHARES);
> vmdef->cputune.sharesSpecified = true;
> }
>
> --
> 1.8.2.1
>
> --
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