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arm64/sve: Skip flushing Z registers with 128 bit vectors

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When the SVE vector length is 128 bits then there are no bits in the Z
registers which are not shared with the V registers so we can skip them
when zeroing state not shared with FPSIMD, this results in a minor
performance improvement.

Signed-off-by: Mark Brown <broonie@kernel.org>
Reviewed-by: Dave Martin <Dave.Martin@arm.com>
Acked-by: Catalin Marinas <catalin.marinas@arm.com>
Link: https://lore.kernel.org/r/20210512151131.27877-4-broonie@kernel.org
Signed-off-by: Will Deacon <will@kernel.org>
This commit is contained in:
Mark Brown 2021-05-12 16:11:31 +01:00 committed by Will Deacon
parent c9f6890bca
commit ad4711f962
3 changed files with 15 additions and 5 deletions
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2
arch/arm64/include/asm/fpsimd.h
View file

@ -69,7 +69,7 @@ static inline void *sve_pffr(struct thread_struct *thread)
extern void sve_save_state(void *state, u32 *pfpsr);
extern void sve_load_state(void const *state, u32 const *pfpsr,
unsigned long vq_minus_1);
extern void sve_flush_live(void);
extern void sve_flush_live(unsigned long vq_minus_1);
extern void sve_load_from_fpsimd_state(struct user_fpsimd_state const *state,
unsigned long vq_minus_1);
extern unsigned int sve_get_vl(void);

12
arch/arm64/kernel/entry-fpsimd.S
View file

@ -69,10 +69,18 @@ SYM_FUNC_START(sve_load_from_fpsimd_state)
ret
SYM_FUNC_END(sve_load_from_fpsimd_state)
/* Zero all SVE registers but the first 128-bits of each vector */
/*
* Zero all SVE registers but the first 128-bits of each vector
*
* VQ must already be configured by caller, any further updates of VQ
* will need to ensure that the register state remains valid.
*
* x0 = VQ - 1
*/
SYM_FUNC_START(sve_flush_live)
cbz x0, 1f // A VQ-1 of 0 is 128 bits so no extra Z state
sve_flush_z
sve_flush_p_ffr
1: sve_flush_p_ffr
ret
SYM_FUNC_END(sve_flush_live)

6
arch/arm64/kernel/fpsimd.c
View file

@ -957,8 +957,10 @@ void do_sve_acc(unsigned int esr, struct pt_regs *regs)
* disabling the trap, otherwise update our in-memory copy.
*/
if (!test_thread_flag(TIF_FOREIGN_FPSTATE)) {
sve_set_vq(sve_vq_from_vl(current->thread.sve_vl) - 1);
sve_flush_live();
unsigned long vq_minus_one =
sve_vq_from_vl(current->thread.sve_vl) - 1;
sve_set_vq(vq_minus_one);
sve_flush_live(vq_minus_one);
fpsimd_bind_task_to_cpu();
} else {
fpsimd_to_sve(current);