Messages in this thread | | | Date | Tue, 25 Jun 2002 10:03:38 -0700 | From | Andrew Morton <> | Subject | Re: efficient copy_to_user and copy_from_user routines in Linux Kernel |
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Mala Anand wrote: > > Here is a 2.5.19 patch that improves the performance of IA32 copy_to_user > and copy_from_user routines used by : > > (1) tcpip protocol stack > (2) file systems >
This came up about a year back when zerocopy networking was merged. Intel boxes started running more slowly purely because of the 8+8 alignment thing.
I changed tcp to use a different copy if either source or dest were not eight-byte aligned, and found that the resulting improvement across a mixed networking load was only 1%. Your numbers are higher, so perhaps there are different alignments in the mix...
One question: have you tested on other CPU types? This problem is very specific to Intel hardware. On AMD, the eight-byte alignement artifact does not exist at all. It could be that your patch is not desirable on such CPUs?
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