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powerpc/32: Don't use lmw/stmw for saving/restoring non volatile regs

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[ Upstream commit a85c728cb5 ]

Instructions lmw/stmw are interesting for functions that are rarely
used and not in the cache, because only one instruction is to be
copied into the instruction cache instead of 19. However those
instruction are less performant than 19x raw lwz/stw as they require
synchronisation plus one additional cycle.

SAVE_NVGPRS / REST_NVGPRS are used in only a few places which are
mostly in interrupts entries/exits and in task switch so they are
likely already in the cache.

Using standard lwz improves null_syscall selftest by:
- 10 cycles on mpc832x.
- 2 cycles on mpc8xx.

Signed-off-by: Christophe Leroy <christophe.leroy@csgroup.eu>
Signed-off-by: Michael Ellerman <mpe@ellerman.id.au>
Link: https://lore.kernel.org/r/316c543b8906712c108985c8463eec09c8db577b.1629732542.git.christophe.leroy@csgroup.eu
Signed-off-by: Sasha Levin <sashal@kernel.org>
This commit is contained in:
Christophe Leroy 2021-08-23 15:29:12 +00:00 • committed by Justin Hammond
parent 0628f92786
commit c3f5b6dce4
1 changed files with 2 additions and 2 deletions
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4
arch/powerpc/include/asm/ppc_asm.h
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@ -28,8 +28,8 @@
#else
#define SAVE_GPR(n, base) stw n,GPR0+4*(n)(base)
#define REST_GPR(n, base) lwz n,GPR0+4*(n)(base)
#define SAVE_NVGPRS(base) stmw 13, GPR0+4*13(base)
#define REST_NVGPRS(base) lmw 13, GPR0+4*13(base)
#define SAVE_NVGPRS(base) SAVE_GPR(13, base); SAVE_8GPRS(14, base); SAVE_10GPRS(22, base)
#define REST_NVGPRS(base) REST_GPR(13, base); REST_8GPRS(14, base); REST_10GPRS(22, base)
#endif
#define SAVE_2GPRS(n, base) SAVE_GPR(n, base); SAVE_GPR(n+1, base)