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Pádraig Brady
2b1c059e6a
A good reference for the concepts used here is: https://mazzo.li/posts/fast-pipes.html We don't consider huge pages or busy loops here, but use vmsplice(), and splice() to get significant speedups: i7-5600U-laptop $ taskset 1 yes | taskset 2 pv > /dev/null ... [4.98GiB/s] i7-5600U-laptop $ taskset 1 src/yes | taskset 2 pv > /dev/null ... [34.1GiB/s] IBM,9043-MRX $ taskset 1 yes | taskset 2 pv > /dev/null ... [11.6GiB/s] IBM,9043-MRX $ taskset 1 src/yes | taskset 2 pv > /dev/null ... [175GiB/s] Also throughput to file (on BTRFS) was seen to increase significantly. With a Fedora 43 laptop improving from 690MiB/s to 1.1GiB/s. * bootstrap.conf: Ensure sys/uio.h is present. This was an existing transitive dependency. * m4/jm-macros.m4: Define HAVE_SPLICE appropriately. We assume vmsplice() is available if splice() is as they were introduced at the same time to Linux and glibc. * src/yes.c (repeat_pattern): A new function to efficiently duplicate a pattern in a buffer with memcpy calls that double in size. This also makes the setup for the existing write() path more efficient. (pipe_splice_size): A new function to increase the kernel pipe buffer if possible, and use an appropriately sized buffer based on that (25%). (splice_write): A new function to call vmplice() when outputting to a pipe, and also splice() if outputting to a non-pipe. * tests/misc/yes.sh: Verify the non-pipe output case, (main): Adjust to always calling write on the minimal buffer first, then trying vmsplice(), then falling back to write from bigger buffer. and the vmsplice() fallback to write() case. * NEWS: Mention the improvement.