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authorNicolas Pitre <nico@cam.org>2009-05-29 21:55:50 -0400
committerNicolas Pitre <nico@cam.org>2009-05-30 01:10:15 -0400
commitc626e3f5ca1d95ad2204d3128c26e7678714eb55 (patch)
tree7c75da068ff30389e1801a3801bd45d38ccae7a7 /drivers
parentcb9dc92c0a1b76165c8c334402e27191084b2047 (diff)
[ARM] alternative copy_to_user: more precise fallback threshold
Previous size thresholds were guessed from various user space benchmarks using a kernel with and without the alternative uaccess option. This is however not as precise as a kernel based test to measure the real speed of each method. This adds a simple test bench to show the time needed for each method. With this, the optimal size treshold for the alternative implementation can be determined with more confidence. It appears that the optimal threshold for both copy_to_user and clear_user is around 64 bytes. This is not a surprise knowing that the memcpy and memset implementations need at least 64 bytes to achieve maximum throughput. One might suggest that such test be used to determine the optimal threshold at run time instead, but results are near enough to 64 on tested targets concerned by this alternative copy_to_user implementation, so adding some overhead associated with a variable threshold is probably not worth it for now. Signed-off-by: Nicolas Pitre <nico@marvell.com>
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