Specifications

Administration Guide
334 VMware, Inc.
By!default,!the!setting!for!high!is!twice!that!of!normal,!or!four!times!that!of!low.!For!
example,!a!virtual!machine!with!high!shares!can!consume!twice!as!many!CPU!cycles!as!
a!virtual!machine!with!normal!shares,!or!four!times!as!many!CPU!cycles!as!a!virtual!
machine
!with!low!shares.!To!change!these!defaults,!see!“Using!procfs”!on!page 339.
You!can!use!proportional‐share!scheduling!by!itself,!or!in!combination!with!CPU!
percentages.!See!“Managing!CPU!Time!with!Percentages!and!Shares”!on!page 334
For!example,!if!you!are!running!three!virtual!machines,!each!starts!with!a!default!
allocation!
of!normal!shares.!To!give!one!virtual!machine!half!the!CPU!time!and!give!
each!of!the!other!two!virtual!machines!one‐quarter!of!the!CPU!time,!assign!high!shares!
to!the!first!virtual!machine!and!leave!the!other!two!at!their!default!allocations.!Because!
these!share!allocations!are!relative,!the
!same!effect!can!be!achieved!by!giving!500!shares!
to!the!first!virtual!machine!and!250!to!each!of!the!other!two!virtual!machines.!
Controlling Relative CPU Rates
You!can!control!relative!CPU!rates!by!specifying!the!number!of!shares!allocated!to!each!
virtual!machine.!Increasing!the!number!of!shares!allocated!to!a!virtual!machine!dilutes!
the!effective!value!of!all!shares!by!increasing!the!total!number!of!shares.!
The!service!console!receives!2000!shares!and!has!a!minimum
!CPU!percentage!of!8!
percent,!by!default.!In!most!cases,!this!should!be!an!appropriate!allocation,!because!the!
service!console!should!not!be!used!for!CPU‐intensive!tasks.!
If!you!need!to!adjust!the!service!console’s!allocation!of!CPU!shares,!use!the!VMware!
Management!Interface!or!the!procfs!interface!on!
the!service!console,!as!described!in!
this!section.!Through!the!management!interface,!you!can!increase!the!minimum!CPU!
percentage!or!the!number!of!CPU!shares!to!allocated!more!CPU!to!the!service!console.!
See!“Managing!the!Service!Console”!on!page 168.
For!example,!suppose!virtual!machine!A!is!allocated!high!shares,!while
!virtual!machine!
B!is!allocated!normal!shares.!If!both!virtual!machines!are!CPU‐bound—that!is,!both!are!
running!the!same!compute‐intensive!benchmark—virtual!machine!A!should!run!twice!
as!fast!as!virtual!machine!B.!If!virtual!machine!A!instead!runs!an!I/O‐bound!workload!
that!causes!it!to!stop!as!
it!waits!for!other!resources,!it!does!not!run!twice!as!fast!as!virtual!
machine!B,!even!though!it!is!allowed!to!use!twice!as!much!CPU!time.!
Managing CPU Time with Percentages and Shares
You!can!use!both!CPU!percentages!and!shares!to!manage!CPU!resources!for!your!
virtual!machines.!CPU!percentages!specify!absolutes,!an!absolute!minimum!or!
N
OTE CPU!share!allocations,!by!themselves,!do!not!guarantee!the!rate!of!progress!within!a!
virtual!machine.!