Re: [libvirt] [PATCH RFC 0/5] support cpu bandwidth in libvirt
At 06/16/2011 03:47 AM, Adam Litke Write:
On 06/15/2011 01:24 AM, Wen Congyang wrote:
> I need this feature immediately after CFS bandwidth patchset is merged into
> upstream kernel. So I prepare this patchset, and post it here for reviewing
> before CFS bandwidth is merged into upstream kernel.
>
> quota is an optional attribute specified in microseconds not a percentage of period.
>
> TODO:
> 1. quota should be in the range [1000, 18446744073709551(2^64/1000)] or less than 0.
> But I only limit it less or equal than 2^64/1000. Does anyone have a better
> way to limit quota?
What are the semantics of quota < 0, of quota == 0? How are you storing
From Documentation/scheduler/sched-bwc.txt:
=======================================
A group with cpu.cfs_quota_us as -1 indicates that the group has infinite
bandwidth, which means that it is not bandwidth controlled.
Writing any negative value to cpu.cfs_quota_us will turn the group into
an infinite bandwidth group. Reading cpu.cfs_quota_us for an infinite
bandwidth group will always return -1.
=======================================
quota == 0 is invalid.
such a large signed integer in the kernel? I will guess that any
value
In the kernel, the value of quota is stored in uint64_t:
=======================================
struct cfs_bandwidth {
#ifdef CONFIG_CFS_BANDWIDTH
raw_spinlock_t lock;
ktime_t period;
u64 quota; <========== here is u64, not s64
u64 runtime;
u64 runtime_expires;
s64 hierarchal_quota;
int idle;
struct hrtimer period_timer, slack_timer;
struct list_head throttled_cfs_rq;
/* statistics */
int nr_periods, nr_throttled;
u64 throttled_time;
#endif
};
=======================================
The unit of quota in kernel is ns, but the value we write to cpu.cfs_quota_us is us.
So the max value we can write is 2^64/1000.
In the kernel, if quota is ~0ULL, it means unlimited.
less than 0 means: no limit, and 0 means: no quota (ie. the cgroup
cannot run on the cpu).
If the kernel does not support CFS bandwidth, quota is 0 and we do not allow user to
modify it. 0 is internal value, and the user does not know it.
I am not sure what the libvirt convention for dealing with a situation
like this is. I think you have two options: 1) override an invalid
value (ie. 1) to represent the case (n < 0) or, 2) use a struct to
represent the quota:
I do not think so. The value that user can specify should be the similar the user
can write it to cpu.cfs_quota_us. If so, the user can use it easily.
struct _virCfsQuota {
unsigned long long val;
int unlimited;
};
When the quota is unlimited, .unlimited == 1 and val is undefined.
Otherwise, the quota is in val.
>
> Wen Congyang (5):
> cgroup: Implement cpu.cfs_period_us and cpu.cfs_quota_us tuning API
> Update XML Schema for new entries
> qemu: Implement period and quota tunable XML configuration and
> parsing.
> qemu: Implement cfs_period and cfs_quota's modification
> doc: Add documentation for new cputune elements period and quota
>
> docs/formatdomain.html.in | 19 +++
> docs/schemas/domain.rng | 25 ++++-
> src/conf/domain_conf.c | 20 +++-
> src/conf/domain_conf.h | 2 +
> src/libvirt_private.syms | 4 +
> src/qemu/qemu_cgroup.c | 43 +++++-
> src/qemu/qemu_driver.c | 162 +++++++++++++++++++----
> src/util/cgroup.c | 81 +++++++++++-
> src/util/cgroup.h | 6 +
> tests/qemuxml2argvdata/qemuxml2argv-cputune.xml | 2 +
> 10 files changed, 328 insertions(+), 36 deletions(-)