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

[Martin Kletzander]

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?

Martin

>Signed-off-by: Dongsheng Yang <yangds.fnst at 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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>libvir-list at redhat.com
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