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If vertical cpu polarization is active then the hypervisor will dispatch certain cpus for a longer time than other cpus for maximum performance. For example if a guest would have three virtual cpus, each of them with a share of 33 percent, then in case of vertical cpu polarization all of the processing time would be combined to a single cpu which would run all the time, while the other two cpus would get nearly no cpu time. There are three different types of vertical cpus: high, medium and low. Low cpus hardly get any real cpu time, while high cpus get a full real cpu. Medium cpus get something in between. In order to switch between the two possible modes (default is horizontal) a 0 for horizontal polarization or a 1 for vertical polarization must be written to the dispatching sysfs attribute: /sys/devices/system/cpu/dispatching The polarization of each single cpu can be figured out by the polarization sysfs attribute of each cpu: /sys/devices/system/cpu/cpuX/polarization horizontal, vertical:high, vertical:medium, vertical:low or unknown. When switching polarization the polarization attribute may contain the value unknown until the configuration change is done and the kernel has figured out the new polarization of each cpu. Note that running a system with different types of vertical cpus may result in significant performance regressions. If possible only one type of vertical cpus should be used. All other cpus should be offlined. Signed-off-by: Martin Schwidefsky <schwidefsky@de.ibm.com> Signed-off-by: Heiko Carstens <heiko.carstens@de.ibm.com> |
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