Bryce Harrington wrote: > On Sun, Oct 08, 2006 at 03:40:56PM +0200, Sebastien Godard wrote: > >> To know exactly how things work, could you please do the following and >> then send me the various snapshots you got: >> 0) CPU's 0 and 1 online. >> 1) Take snapshot #1 of /proc/stat file >> 2) Disable CPU 1 >> 3) Take snapshot #2 of /proc/stat >> 4) Wait a few (2-3...) seconds >> 5) Take snapshot #3 of /proc/stat >> 6) Enable CPU 1 >> 7) Take snapshot #4 of /proc/stat >> > > I've done the above for two different systems for comparison. The > capture script is also attached. > Thanks a lot. This will be useful for me to know how to update sysstat code. > > >> Also could you tell me if there is a specific processor (for example CPU >> 0) that can *never* be disabled? >> > > No, but this is architecture dependent. All systems prevent you from > offlining ALL cpus, but some (like em64t) restrict offlining cpu0, while > others (ppc64 for example) simply require that any one cpu remain > online, and do allow offlining cpu0. > This is a real difficulty... sar has to compute the interval of time elapsed since its previous sample, and needs for this a processor that has never been disabled during this interval of time. So this will be a limit for sar, which will assume that one cpu (cpu0) can never be disabled. I'm going to update sysstat in the coming days (or weeks, depending on the free time I have). I will submit it to you so that you can try it on your systems. Regards, -- Sébastien Godard (sysstat <at> wanadoo.fr) http://perso.orange.fr/sebastien.godard/
