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SubjectRe: [benchmark] 2.4.0-test6-pre1 PAE vs non-PAE

the 3% performance drop is mainly due to two values, 'Pipe-based Context
Switching', 'Process Creation', and 'Execl Throughput'. The fork() and
exec() result is understandably worse with PAE, because the 'density' of
page-tables is half of that of non-PAE page-tables (ie. twice as much has
to be copied), plus there are 3 user-space root page tables instead of the
1. (which have to be zeroed, so this shows up big time.)

Another performance problem is likely the amount of LOCK-ed instructions
done within the PAE include-files - some of that is unnecessery as David
S. Miller noticed.

otherwise the PAE kernels show no performance drop in 'typical' user-space
stuff. But yes, you dont want to use it on a box with less than 4GB RAM.

Ingo


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