Anton Blanchard 5d5fc33ce5 riscv: Improve exception and system call latency ... Many CPUs implement return address branch prediction as a stack. The RISCV architecture refers to this as a return address stack (RAS). If this gets corrupted then the CPU will mispredict at least one but potentally many function returns. There are two issues with the current RISCV exception code: - We are using the alternate link stack (x5/t0) for the indirect branch which makes the hardware think this is a function return. This will corrupt the RAS. - We modify the return address of handle_exception to point to ret_from_exception. This will also corrupt the RAS. Testing the null system call latency before and after the patch: Visionfive2 (StarFive JH7110 / U74) baseline: 189.87 ns patched: 176.76 ns Lichee pi 4a (T-Head TH1520 / C910) baseline: 666.58 ns patched: 636.90 ns Just over 7% on the U74 and just over 4% on the C910. Signed-off-by: Anton Blanchard <antonb@tenstorrent.com> Signed-off-by: Cyril Bur <cyrilbur@tenstorrent.com> Tested-by: Jisheng Zhang <jszhang@kernel.org> Reviewed-by: Jisheng Zhang <jszhang@kernel.org> Link: https://lore.kernel.org/r/20240607061335.2197383-1-cyrilbur@tenstorrent.com Signed-off-by: Palmer Dabbelt <palmer@rivosinc.com>		2024-07-26 05:50:45 -07:00
..
boot	riscv: boot: remove duplicated targets line	2024-07-24 06:14:06 -07:00
configs	RISC-V: run savedefconfig for defconfig	2024-07-22 10:57:47 -07:00
crypto	crypto: riscv - add vector crypto accelerated AES-CBC-CTS	2024-03-20 08:56:11 -07:00
errata	riscv: Extend cpufeature.c to detect vendor extensions	2024-07-22 15:36:54 -07:00
include	Merge patch series "riscv: Separate vendor extensions from standard extensions"	2024-07-22 15:37:01 -07:00
kernel	riscv: Improve exception and system call latency	2024-07-26 05:50:45 -07:00
kvm	RISC-V Patches for the 6.11 Merge Window, Part 1	2024-07-20 09:11:27 -07:00
lib	riscv: Optimize crc32 with Zbc extension	2024-07-10 13:19:50 -07:00
mm	RISC-V Patches for the 6.11 Merge Window, Part 1	2024-07-20 09:11:27 -07:00
net	RISC-V Patches for the 6.11 Merge Window, Part 1	2024-07-20 09:11:27 -07:00
purgatory	Makefile: remove redundant tool coverage variables	2024-05-14 23:35:48 +09:00
tools
Kbuild	RISC-V: hook new crypto subdir into build-system	2024-01-22 17:55:17 -08:00
Kconfig	trace: riscv: Remove deprecated kprobe on ftrace support	2024-07-24 06:14:05 -07:00
Kconfig.debug	riscv: Add tests for riscv module loading	2023-11-07 14:59:32 -08:00
Kconfig.errata	riscv: thead: Rename T-Head PBMT to MAE	2024-04-25 10:22:33 -07:00
Kconfig.socs	RISC-V: drop SOC_VIRT for ARCH_VIRT	2024-04-10 11:37:50 +01:00
Kconfig.vendor	riscv: Extend cpufeature.c to detect vendor extensions	2024-07-22 15:36:54 -07:00
Makefile	Merge patch series "riscv: Apply Zawrs when available"	2024-07-12 08:55:29 -07:00
Makefile.postlink	kbuild: remove ARCH_POSTLINK from module builds	2023-10-28 21:10:08 +09:00