Messages in this thread | | | Subject | RE: boot-time slowdown for measure_migration_cost | Date | Fri, 27 Jan 2006 13:48:07 -0800 | From | "Luck, Tony" <> |
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> The boot-time migration cost auto-tuning stuff seems to have > been merged to Linus' tree since 2.6.15. On little one- or > two-processor systems, the time required to measure the > migration costs isn't very noticeable, but by the time we > get to even a four-processor ia64 box, it adds about > 30 seconds to the boot time, which seems like a lot.
I only see about 16 seconds for a 4-way tiger (not that 16 seconds is good ... but it not as bad as 30). This was with a build from tiger_defconfig that sets CONFIG_NR_CPUS=4 ... so I wonder what's causing the factor of two. I measured with a printk each side of build_sched_domains() and booted with the "time" command line arg to get:
[ 0.540718] Building sched domains [ 16.124693] migration_cost=10091 [ 16.124789] Done
More importantly, how does this time scale as the number of cpus increases? Linear, or worse? What happens on a 512 cpu Altix (if it's quadratic, they may be still waiting for the boot to finish :-)
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