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792060de8b
We're spending a considerable amount of the sendmsg/recvmsg time just copying in the message header. And for provided buffers, the known single entry iovec. Be a bit smarter about it and enable/disable user access around our copying. In a test case that does both sendmsg and recvmsg, the runtime before this change (averaged over multiple runs, very stable times however): Kernel Time Diff ==================================== -git 4720 usec -git+commit 4311 usec -8.7% and looking at a profile diff, we see the following: 0.25% +9.33% [kernel.kallsyms] [k] _copy_from_user 4.47% -3.32% [kernel.kallsyms] [k] __io_msg_copy_hdr.constprop.0 where we drop more than 9% of _copy_from_user() time, and consequently add time to __io_msg_copy_hdr() where the copies are now attributed to, but with a net win of 6%. In comparison, the same test case with send/recv runs in 3745 usec, which is (expectedly) still quite a bit faster. But at least sendmsg/recvmsg is now only ~13% slower, where it was ~21% slower before. Signed-off-by: Jens Axboe <axboe@kernel.dk>
Linux kernel
============
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