Messages in this thread | | | Date | Fri, 10 Feb 2006 12:09:39 +0100 | From | Eric Dumazet <> | Subject | Re: [PATCH] percpu data: only iterate over possible CPUs |
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Andrew Morton a écrit : > Andi Kleen <ak@muc.de> wrote: >> On Thursday 09 February 2006 19:04, Andrew Morton wrote: >>> Ashok Raj <ashok.raj@intel.com> wrote: >>>> The problem was with ACPI just simply looking at the namespace doesnt >>>> exactly give us an idea of how many processors are possible in this platform. >>> We need to fix this asap - the performance penalty for HOTPLUG_CPU=y, >>> NR_CPUS=lots will be appreciable. >> What is this performance penalty exactly? > > All those for_each_cpu() loops will hit NR_CPUS cachelines instead of > hweight(cpu_possible_map) cachelines.
You mean NR_CPUS bits, mostly all included in a single cacheline, and even in a single long word :) for most cases (NR_CPUS <= 32 or 64)
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