CPU Ready Time – Blog Part II

posted April 23, 2014, 9:23 AM by

Jim Hannan (@HoBHannan), Principal Architect

This is the follow up blog to CPU Ready Part I. I have been using the following tables for around six months now. I find them very helpful in quickly determining if a virtual machine is having issues with CPU Ready Time.

What is CPU Ready Time?

CPU Ready Time is measured as a summation value in vSphere, different chart time spans will effect the redline value. Here’s a break down of the summations for each time period:

  • Real-time: 20 seconds
  • Past Day: 5 minutes (300 seconds)
  • Past Week: 30 minutes (1800 seconds)
  • Past Month: 2 hours (7200 seconds)
  • Past Year: 1 day (86400 seconds)

This can be time consuming to collect during troubleshooting, so we supplied the redline for each time period in Tables 1-5.

The formula: CPU Ready % = (Summation value / (chart update interval in seconds x 1000)) x 100

Reference: Update intervals (KB article 2002181): http://kb.vmware.com/selfservice/microsites/search.do?language=en_US&cmd=displayKC&externalId=2002181

Table 1 – CPU Ready Time (Real Time)

For CPU Ready Time measured by Real Time the interval is every 20 seconds.

ms (milliseconds) % (percent)
1000 5.0
900 4.5
800 4.0
700 3.5
600 3.0
500 2.5
400 2.0
300 1.5
200 1.0
100 0.5
50 0.25

 

Table 2 – CPU Ready Time (Day)

For CPU Ready Time measured by Day the interval is every 300 seconds.

ms (milliseconds) % (percent)
15000 5.0
13500 4.5
12000 4.0
10500 3.5
9000 3.0
7500 2.5
6000 2.0
4500 1.5
3000 1.0
1500 0.5
750 0.25

 

Table 3 – CPU Ready Time (Week)

For CPU Ready Time measured by Week the interval is every 30 minutes.

ms (milliseconds) % (percent)
90000 5.0
81000 4.5
72000 4.0
63000 3.5
54000 3.0
45000 2.5
36000 2.0
27000 1.5
18000 1.0
9000 0.5
4500 0.25

 

Table 4 – CPU Ready Time (Month)

For CPU Ready Time measured by Month the interval is every 2 hours.

ms (milliseconds) % (percent)
360000 5.0
324000 4.5
288000 4.0
252000 3.5
216000 3.0
180000 2.5
144000 2.0
108000 1.5
72000 1.0
36000 0.5
18100 0.25

 

Table 5 – CPU Ready Time (Year)

For CPU Ready Time measured by Year the interval is every 864000 seconds.

ms (milliseconds) % (percent)
4320000 5.0
3888000 4.5
3456000 4.0
3024000 3.5
2592000 3.0
2160000 2.5
1728000 2.0
1296000 1.5
864000 1.0
432000 0.5
216000 0.25
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2 Comments

  • Pavel says:

    Dear Jim,
    I have read your article with very deep interest.
    We are having numbers (according to Table 1) 3000ms.
    Is there any chance, that behaviour in 6.5 has been changed? And numbers from year 2014 are not valid?
    Because with increasing number of cores (p and v) latency must increase (still one core for scheduling).

    Can you clarify this for me?

    Kind regards,

    Pavel

    • Jim Hannan says:

      Thank you for reading our blog. I suspect the CPU scheduler was enhanced in vSphere 6 as it has been in previous versions. VMware in versions 4 and 5 published a white paper on the CPU scheduler. Let me know if you would like a link to it. That said that the scheduler was enhanced in 6.+ I don’t believe that Ready Time numbers would increase but continue the trend from vSphere 3 and decrease. I am going to do some more research on this and update this blog, probably in the next few weeks.

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