On Sat, Oct 07, 2006 at 02:48:15PM +0200, Sebastien Godard wrote: > Bryce Harrington wrote: > >1. offline a cpu > >2. start sar > >3. online the cpu > >4. The sar output does not display the newly onlined CPU, and > > continues to only show cpu's 0, 1, and 2. > > > >I'm wondering if this is intended behavior? When sar is started with > >all the CPU's onlined, and a cpu is offlined when it runs, then it will > >display 'nan' for that cpu, until it comes back online; this is fine, > >since you can see in the output that a cpu is missing. However if the > >cpu is brought online after sar starts, then the sar output is not > >really providing complete information on the system. How do you think > >sar ought to behave in this situation? > > > No, this is not really intended behavior. In fact sar is just not > "hotplug CPU compliant" and has never been tested on such hardwares... > Anyway I'm really interested to update it so that it can take into > account CPU that get off- or onlined on the fly. But I need to know how > files like /proc/stat for example are changed when a CPU is offlined or > onlined. I would appreciate to get some info about that. Sure, I've attached two snapshots of /proc/stat, one with both cpu's enabled, and one after a cpu has been disabled. This is on the EM64t x86_64 machine. In 2.6.* kernels, it appears that the definitive location for determining available cpu's is in /sys/devices/system/cpu/cpu*/. If the CPU's are hotpluggable, then there is an online file in the directory, and echoing 0 or 1 into that file turns the cpu off or on. Are there test cases for sysstat? If so, I'd be happy to help with testing of sysstat on various architectures, including with cpu and memory hotplugging or with different nfs configurations. Or if login access to the different hardware would be useful, we can arrange that for you. 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