Akira Tsukamoto ca6eaaa210 riscv: __asm_copy_to-from_user: Optimize unaligned memory access and pipeline stall ... This patch will reduce cpu usage dramatically in kernel space especially for application which use sys-call with large buffer size, such as network applications. The main reason behind this is that every unaligned memory access will raise exceptions and switch between s-mode and m-mode causing large overhead. First copy in bytes until reaches the first word aligned boundary in destination memory address. This is the preparation before the bulk aligned word copy. The destination address is aligned now, but oftentimes the source address is not in an aligned boundary. To reduce the unaligned memory access, it reads the data from source in aligned boundaries, which will cause the data to have an offset, and then combines the data in the next iteration by fixing offset with shifting before writing to destination. The majority of the improving copy speed comes from this shift copy. In the lucky situation that the both source and destination address are on the aligned boundary, perform load and store with register size to copy the data. Without the unrolling, it will reduce the speed since the next store instruction for the same register using from the load will stall the pipeline. At last, copying the remainder in one byte at a time. Signed-off-by: Akira Tsukamoto <akira.tsukamoto@gmail.com> Signed-off-by: Palmer Dabbelt <palmerdabbelt@google.com>		2021-07-06 15:09:48 -07:00
..
delay.c	riscv: delay: use do_div() instead of __udivdi3()	2019-08-08 16:05:38 -07:00
error-inject.c	riscv: Add support for function error injection	2021-01-14 15:09:09 -08:00
Makefile	riscv: Add support for function error injection	2021-01-14 15:09:09 -08:00
memcpy.S	riscv: Add KASAN support	2020-01-22 13:09:58 -08:00
memmove.S	riscv: provide memmove implementation	2020-12-10 17:27:54 -08:00
memset.S	riscv: Add KASAN support	2020-01-22 13:09:58 -08:00
tishift.S	riscv: Less inefficient gcc tishift helpers (and export their symbols)	2020-01-18 19:13:41 -08:00
uaccess.S	riscv: __asm_copy_to-from_user: Optimize unaligned memory access and pipeline stall	2021-07-06 15:09:48 -07:00