1 Reply Latest reply on Jan 6, 2012 4:54 AM by Mike Gerdts-Oracle

    What the different of zone.cpu-cap & zone.cpu-shares?

    Rachmat Febrianto-Oracle
      Hi folks,

      anyone who can explain the different of zone.cpu-cap & zone.cpu-shares? I'll be thank for the response.

        • 1. Re: What the different of zone.cpu-cap & zone.cpu-shares?
          Mike Gerdts-Oracle
          In a nutshell, caps set an upper bound and shares set a lower-bound for the amount of CPU that a zone gets.

          As stated in zonecfg(1M):
                   Sets a limit on the amount of CPU time that can be  used
                   by a zone. The unit used translates to the percentage of
                   a single CPU that can be used by all user threads  in  a
                   zone,  expressed  as  a fraction (for example, .75) or a
                   mixed number (whole number and  fraction,  for  example,
                   1.25).  An  ncpu value of 1 means 100% of a CPU, a value
                   of 1.25 means 125%, .75 mean 75%,  and  so  forth.  When
                   projects  within  a capped zone have their own caps, the
                   minimum value takes precedence.
                   The capped-cpu property is  an  alias  for  zone.cpu-cap
                   resource  control  and  is  related  to the zone.cpu-cap
                   resource control. See resource_controls(5).
          If you set a capped-cpu to 2 on a 16 processor machine, the zone will never get to use more than the equivalent of two CPUs. That is, it could end up with lots of things in the run queue while the system has idle processors because the zone has hit its CPU cap.

          zone.cpu-shares interacts with the fair share scheduler. It goes with the idea that a CPU is a terrible thing to waste. By setting the CPU shares for a particular zone to a value, it makes the zone get a minimum of a calculated percent of CPU if it is needed. The percentage that the zone gets is based on:

          (this zone's zone.cpu-shares) / sum(zone.cpu-shares across all zones)

          So, if z1, z2, and z3 are zones with 10 50 and 40 CPU shares, z1 would get at least 10% (10 / (10 + 50 + 40)) of the CPU time, z2 would get 50%, and z3 would get 40%. However, if z2 and z3 are idle, z1 could use 100% of the system's CPU resources.
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