[PATCH 0/3] Report guest steal time in host

Naveen N. Rao
2015-05-06T11:56:33Z

Steal time accounts the time duration during which a guest vcpu was ready to
run, but was not scheduled to run by the hypervisor. This is particularly
relevant in cloud environment where customers would want to use this as an
indicator that their guests are being throttled. However, as it stands today,
guest steal time information is not visible from the hypervisor.

For cloud service providers, this is problematic since they would want to
overcommit cpu resources to achieve optimum resource utilization while at the
same time ensuring guests are not throttled. It is useful for service providers
to have access to the guest steal time data so that they can base their
overcommit/guest packing decisions on this. Higher guest steal time can be used
as a trigger to change how the guests are scheduled, or even migrate guests out
of a system.

This patchset attempts to make the guest steal times available in the host.
This is achieved by introducing a new field in per-task statistics
(/proc/<pid>/stat and /proc/<pid>/task/<pid>/stat) to accumulate per-vcpu steal
time. Programs (such as pidstat) can then be enhanced to report this
information on a per-thread basis.

This should also work for nested virtualization: steal time information for the
guest is readable via /proc/stat, while steal time information for guests
hosted on this hypervisor is readable via /proc/<pid>/task/*/stat.

Also, mpstat always shows steal time information for current (self) guest on a
per-cpu basis. And pidstat can be enhanced to report the same for the hosted
guests on a per-vcpu basis.

As an example:

Guest (self) steal time information using mpstat:
------------------------------------------------

mpstat is run from within the guest.

[root@rhel7-img ~]# mpstat -P ALL 1
Linux 3.19.0nnr (rhel7-img) 04/15/2015 _ppc64_ (4 CPU)

03:13:23 PM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
03:13:24 PM all 12.25 0.00 1.25 0.00 1.00 2.25 13.75 0.00 0.00 69.50
03:13:24 PM 0 46.53 0.00 0.00 0.00 0.00 4.95 45.54 0.00 0.00 2.97
03:13:24 PM 1 0.00 0.00 0.00 0.00 0.00 4.04 3.03 0.00 0.00 92.93
03:13:24 PM 2 0.00 0.00 0.00 0.00 3.96 0.99 2.97 0.00 0.00 92.08
03:13:24 PM 3 3.00 0.00 4.00 0.00 0.00 0.00 4.00 0.00 0.00 89.00

03:13:24 PM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
03:13:25 PM all 12.59 0.00 0.00 0.00 0.00 0.25 12.35 0.00 0.00 74.81
03:13:25 PM 0 50.00 0.00 0.00 0.00 0.00 0.98 49.02 0.00 0.00 0.00
03:13:25 PM 1 0.98 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 99.02
03:13:25 PM 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
03:13:25 PM 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00

03:13:25 PM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
03:13:26 PM all 12.99 0.00 0.00 0.00 0.25 0.00 12.75 0.00 0.00 74.02
03:13:26 PM 0 51.96 0.00 0.00 0.00 0.00 0.00 48.04 0.00 0.00 0.00
03:13:26 PM 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
03:13:26 PM 2 0.00 0.00 0.00 0.00 0.98 0.00 2.94 0.00 0.00 96.08
03:13:26 PM 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00

03:13:26 PM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
03:13:27 PM all 12.53 0.00 1.00 0.25 0.00 0.25 12.03 0.00 0.00 73.93
03:13:27 PM 0 51.02 0.00 0.00 0.00 0.00 0.00 48.98 0.00 0.00 0.00
03:13:27 PM 1 0.00 0.00 4.04 0.00 0.00 0.00 0.00 0.00 0.00 95.96
03:13:27 PM 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
03:13:27 PM 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00

Average: CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
Average: all 12.91 0.00 0.54 0.01 0.04 0.12 12.39 0.00 0.00 74.00
Average: 0 51.36 0.00 0.03 0.00 0.03 0.26 48.27 0.00 0.00 0.05
Average: 1 0.02 0.00 1.54 0.02 0.02 0.15 0.36 0.00 0.00 97.89
Average: 2 0.00 0.00 0.52 0.00 0.09 0.02 0.36 0.00 0.00 99.02
Average: 3 0.05 0.00 0.07 0.00 0.02 0.09 0.34 0.00 0.00 99.43

Steal time information for hosted guests in host using (locally modified) pidstat:
---------------------------------------------------------------------------------

pidstat is being run in the host.

[naveen@xxxxxxxxxx sysstat]$ ./pidstat -C qemu -tIu 1
Linux 3.19.0nnr (xxxxxxxxxx.in.ibm.com) 04/15/2015 _ppc64_ (64 CPU)

04:43:20 AM UID TGID TID %usr %system %guest %CPU %steal CPU Command
04:43:22 AM 1008 3001 - 0.00 0.00 54.21 3.39 45.79 12 qemu-system-ppc
04:43:22 AM 1008 - 3005 0.00 0.00 54.21 3.39 0.00 12 |__qemu-system-ppc

04:43:22 AM UID TGID TID %usr %system %guest %CPU %steal CPU Command
04:43:23 AM 1008 3001 - 0.00 0.00 52.00 3.25 46.00 12 qemu-system-ppc
04:43:23 AM 1008 - 3003 0.00 0.00 2.00 0.12 46.00 12 |__qemu-system-ppc
04:43:23 AM 1008 - 3005 0.00 0.00 45.00 2.81 0.00 12 |__qemu-system-ppc
04:43:23 AM 1008 - 3006 0.00 0.00 6.00 0.38 0.00 12 |__qemu-system-ppc

04:43:23 AM UID TGID TID %usr %system %guest %CPU %steal CPU Command
04:43:24 AM 1008 3001 - 0.00 2.00 50.00 3.25 67.00 12 qemu-system-ppc
04:43:24 AM 1008 - 3001 0.00 1.00 0.00 0.06 0.00 12 |__qemu-system-ppc
04:43:24 AM 1008 - 3003 0.00 0.00 8.00 0.50 49.00 12 |__qemu-system-ppc
04:43:24 AM 1008 - 3004 0.00 0.00 2.00 0.12 5.00 12 |__qemu-system-ppc
04:43:24 AM 1008 - 3005 0.00 0.00 38.00 2.38 3.00 12 |__qemu-system-ppc
04:43:24 AM 1008 - 3006 0.00 1.00 0.00 0.06 8.00 12 |__qemu-system-ppc

04:43:24 AM UID TGID TID %usr %system %guest %CPU %steal CPU Command
04:43:25 AM 1008 3001 - 0.00 0.00 51.00 3.19 47.00 12 qemu-system-ppc
04:43:25 AM 1008 - 3003 0.00 0.00 27.00 1.69 47.00 12 |__qemu-system-ppc
04:43:25 AM 1008 - 3004 0.00 1.00 0.00 0.06 0.00 12 |__qemu-system-ppc
04:43:25 AM 1008 - 3005 0.00 1.00 23.00 1.50 0.00 12 |__qemu-system-ppc
04:43:25 AM 1008 - 3006 0.00 0.00 2.00 0.12 0.00 12 |__qemu-system-ppc

04:43:25 AM UID TGID TID %usr %system %guest %CPU %steal CPU Command
04:43:26 AM 1008 3001 - 0.00 0.00 51.00 3.18 53.00 12 qemu-system-ppc
04:43:26 AM 1008 - 3003 0.00 0.00 9.00 0.56 50.00 12 |__qemu-system-ppc
04:43:26 AM 1008 - 3005 0.00 0.00 16.00 1.00 3.00 12 |__qemu-system-ppc
04:43:26 AM 1008 - 3006 0.00 0.00 26.00 1.62 0.00 12 |__qemu-system-ppc

Average: UID TGID TID %usr %system %guest %CPU %steal CPU Command
Average: 1008 3001 - 0.00 0.18 51.54 3.23 50.12 - qemu-system-ppc
Average: 1008 - 3001 0.02 0.02 0.00 0.00 0.00 - |__qemu-system-ppc
Average: 1008 - 3003 0.00 0.03 15.89 0.99 48.24 - |__qemu-system-ppc
Average: 1008 - 3004 0.00 0.05 11.70 0.73 0.56 - |__qemu-system-ppc
Average: 1008 - 3005 0.00 0.06 20.03 1.26 0.58 - |__qemu-system-ppc
Average: 1008 - 3006 0.00 0.03 3.93 0.25 0.72 - |__qemu-system-ppc

- Naveen

------
Changes since RFC: Updated description to clarify few aspects that I got
questions about. No code changes.

Naveen N. Rao (3):
procfs: add guest steal time in /proc/<pid>/stat
kvm/x86: report guest steal time in host
kvm/powerpc: report guest steal time in host

arch/powerpc/include/asm/kvm_host.h | 1 +
arch/powerpc/kernel/asm-offsets.c | 1 +
arch/powerpc/kvm/book3s_hv.c | 2 ++
arch/powerpc/kvm/book3s_hv_rmhandlers.S | 3 +++
arch/x86/kvm/x86.c | 1 +
fs/proc/array.c | 6 ++++++
include/linux/sched.h | 7 +++++++
kernel/fork.c | 2 +-
8 files changed, 22 insertions(+), 1 deletion(-)

--
2.3.7