x86/entry: Test ti_work for zero before processing individual bits

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In most cases, ti_work values passed to arch_exit_to_user_mode_prepare()
are zeros, e.g., 99% in kernel build tests.  So an obvious optimization is
to test ti_work for zero before processing individual bits in it.

Omit the optimization when FPU debugging is enabled, otherwise the
FPU consistency check is never executed.

Intel 0day tests did not find a perfermance regression with this change.

Suggested-by: H. Peter Anvin (Intel) <hpa@zytor.com>
Signed-off-by: Xin Li (Intel) <xin@zytor.com>
Signed-off-by: Thomas Gleixner <tglx@linutronix.de>
Link: https://lore.kernel.org/all/20240822073906.2176342-2-xin@zytor.com

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Xin Li (Intel) 2024-08-22 00:39:04 -07:00 • committed by Thomas Gleixner

parent 723edbd2ca

commit 0dfac6f267

1 changed files with 8 additions and 2 deletions

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arch/x86/include/asm/entry-common.h

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