[PATCH v1 0/4] Linear and Logarithmic histogram statistics

[Jing Zhang <jingzhangos@google.com>]

This patchset adds linear and logarithmic histogram stats support and extend
some halt polling stats with histogram.
Histogram stats is very useful when we need to know the distribution of some
latencies or any other stuff like used memory size, huge page size, etc.
Below is a snapshot for three logarithmic histogram stats added in this
patchset. halt_poll_success_hist shows the distribution of wait time before a
success polling. halt_poll_fail_hist shows the distribution of wait time before
a fail polling. halt_wait_hist shows the distribution of wait time of a VCPU
spending on wait after it is halted. The halt polling parameters is halt_poll_ns
= 500000, halt_poll_ns_grow = 2, halt_poll_ns_grow_start = 10000,
halt_poll_ns_shrink = 2;
From the snapshot, not only we can get an intuitive overview of those latencies,
but also we can tune the polling parameters based on this; For example, it shows
that about 80% of successful polling is less than 132000 nanoseconds from
halt_poll_success_hist, then it might be a good option to set halt_poll_ns as
132000 instead of 500000.

halt_poll_success_hist:
Range		Bucket Value	Percent     Cumulative Percent
[0, 1)		 0		 0.000%      0.000%
[1, 2)		 0		 0.000%      0.000%
[2, 4)		 0		 0.000%      0.000%
[4, 8)		 0		 0.000%      0.000%
[8, 16)		 0		 0.000%      0.000%
[16, 32)	 0		 0.000%      0.000%
[32, 64)	 0		 0.000%      0.000%
[64, 128)	 0		 0.000%      0.000%
[128, 256)	 3		 0.093%      0.093%
[256, 512)	 21		 0.650%      0.743%
[512, 1024)	 43		 1.330%      2.073%
[1024, 2048)	 279		 8.632%      10.705%
[2048, 4096)	 253		 7.828%      18.533%
[4096, 8192)	 595		 18.410%     36.943%
[8192, 16384)	 274		 8.478%      45.421%
[16384, 32768)	 351		 10.860%     56.281%
[32768, 65536)	 343		 10.613%     66.894%
[65536, 131072)  421		 13.026%     79.920%
[131072, 262144) 459		 14.202%     94.121%
[262144, 524288) 190		 5.879%      100.000%


halt_poll_fail_hist:
Range		Bucket Value	Percent     Cumulative Percent
[0, 1)		 0		 0.000%      0.000%
[1, 2)		 0		 0.000%      0.000%
[2, 4)		 0		 0.000%      0.000%
[4, 8)		 0		 0.000%      0.000%
[8, 16)		 0		 0.000%      0.000%
[16, 32)	 0		 0.000%      0.000%
[32, 64)	 0		 0.000%      0.000%
[64, 128)	 21		 0.529%      0.529%
[128, 256)	 398		 10.020%     10.549%
[256, 512)	 613		 15.433%     25.982%
[512, 1024)	 437		 11.002%     36.984%
[1024, 2048)	 264		 6.647%      43.630%
[2048, 4096)	 302		 7.603%      51.234%
[4096, 8192)	 350		 8.812%      60.045%
[8192, 16384)	 488		 12.286%     72.331%
[16384, 32768)	 258		 6.495%      78.827%
[32768, 65536)	 227		 5.715%      84.542%
[65536, 131072)  232		 5.841%      90.383%
[131072, 262144) 246		 6.193%      96.576%
[262144, 524288) 136		 3.424%      100.000%


halt_wait_hist:
Range			    Bucket Value    Percent	Cumulative Percent
[0, 1)			     0		     0.000%	 0.000%
[1, 2)			     0		     0.000%	 0.000%
[2, 4)			     0		     0.000%	 0.000%
[4, 8)			     0		     0.000%	 0.000%
[8, 16)			     0		     0.000%	 0.000%
[16, 32)		     0		     0.000%	 0.000%
[32, 64)		     0		     0.000%	 0.000%
[64, 128)		     0		     0.000%	 0.000%
[128, 256)		     0		     0.000%	 0.000%
[256, 512)		     0		     0.000%	 0.000%
[512, 1024)		     0		     0.000%	 0.000%
[1024, 2048)		     0		     0.000%	 0.000%
[2048, 4096)		     7		     0.127%	 0.127%
[4096, 8192)		     37		     0.671%	 0.798%
[8192, 16384)		     69		     1.251%	 2.049%
[16384, 32768)		     94		     1.704%	 3.753%
[32768, 65536)		     150	     2.719%	 6.472%
[65536, 131072)		     233	     4.224%	 10.696%
[131072, 262144)	     276	     5.004%	 15.700%
[262144, 524288)	     236	     4.278%	 19.978%
[524288, 1.04858e+06)	     176	     3.191%	 23.169%
[1.04858e+06, 2.09715e+06)   94		     16.207%	 39.376%
[2.09715e+06, 4.1943e+06)    1667	     30.221%	 69.598%
[4.1943e+06, 8.38861e+06)    825	     14.956%	 84.554%
[8.38861e+06, 1.67772e+07)   111	     2.012%	 86.566%
[1.67772e+07, 3.35544e+07)   76		     1.378%	 87.944%
[3.35544e+07, 6.71089e+07)   65		     1.178%	 89.123%
[6.71089e+07, 1.34218e+08)   161	     2.919%	 92.041%
[1.34218e+08, 2.68435e+08)   250	     4.532%	 96.574%
[2.68435e+08, 5.36871e+08)   188	     3.408%	 99.982%
[5.36871e+08, 1.07374e+09)   1		     0.018%	 100.000%

---

Jing Zhang (4):
  KVM: stats: Support linear and logarithmic histogram statistics
  KVM: stats: Update doc for histogram statistics
  KVM: selftests: Add checks for histogram stats parameters
  KVM: stats: Add halt polling related histogram stats

 Documentation/virt/kvm/api.rst                | 36 ++++++++++-
 arch/arm64/kvm/guest.c                        |  4 --
 arch/mips/kvm/mips.c                          |  4 --
 arch/powerpc/include/asm/kvm_host.h           |  1 -
 arch/powerpc/kvm/book3s.c                     |  5 --
 arch/powerpc/kvm/book3s_hv.c                  | 20 +++++-
 arch/powerpc/kvm/booke.c                      |  5 --
 arch/s390/kvm/kvm-s390.c                      |  4 --
 arch/x86/kvm/x86.c                            |  4 --
 include/linux/kvm_host.h                      | 62 ++++++++++++++-----
 include/linux/kvm_types.h                     | 20 ++++++
 include/uapi/linux/kvm.h                      | 11 +++-
 .../selftests/kvm/kvm_binary_stats_test.c     | 17 +++++
 virt/kvm/binary_stats.c                       | 36 +++++++++++
 virt/kvm/kvm_main.c                           | 19 ++++++
 15 files changed, 196 insertions(+), 52 deletions(-)


base-commit: 7caa04b36f204a01dac65582b71d26d190a1e022
-- 
2.32.0.93.g670b81a890-goog