From: Will Deacon <will.deacon@arm.com>
To: linux-arm-kernel@lists.infradead.org
Cc: linux-kernel@vger.kernel.org, ard.biesheuvel@linaro.org,
catalin.marinas@arm.com, rml@tech9.net, tglx@linutronix.de,
peterz@infradead.org, schwidefsky@de.ibm.com,
Will Deacon <will.deacon@arm.com>
Subject: [PATCH 0/2] arm64: Only call into preempt_schedule() if need_resched()
Date: Tue, 27 Nov 2018 19:45:00 +0000 [thread overview]
Message-ID: <1543347902-21170-1-git-send-email-will.deacon@arm.com> (raw)
Hi all,
This pair of patches improves our preempt_enable() implementation slightly
on arm64 by making the resulting call to preempt_schedule() conditional
on need_resched(), which is tracked in bit 32 of the preempt count. The
logic is inverted so that we can detect the preempt count going to zero
and need_resched being set with a single CBZ instruction.
Consequently, our preempt_enable() code (including prologue/epilogue)
goes from:
40: a9bf7bfd stp x29, x30, [sp, #-16]!
44: 910003fd mov x29, sp
48: d5384101 mrs x1, sp_el0
4c: b9401020 ldr w0, [x1, #16]
50: 51000400 sub w0, w0, #0x1
54: b9001020 str w0, [x1, #16]
58: 350000a0 cbnz w0, 6c
5c: f9400020 ldr x0, [x1]
60: 721f001f tst w0, #0x2
64: 54000040 b.eq 6c // b.none
68: 94000000 bl 0 <preempt_schedule>
6c: a8c17bfd ldp x29, x30, [sp], #16
70: d65f03c0 ret
to:
40: a9bf7bfd stp x29, x30, [sp, #-16]!
44: 910003fd mov x29, sp
48: d5384101 mrs x1, sp_el0
4c: f9400820 ldr x0, [x1, #16]
50: d1000400 sub x0, x0, #0x1
54: b9001020 str w0, [x1, #16]
58: b4000060 cbz x0, 64 <will+0x24>
5c: a8c17bfd ldp x29, x30, [sp], #16
60: d65f03c0 ret
64: 94000000 bl 0 <preempt_schedule>
68: a8c17bfd ldp x29, x30, [sp], #16
6c: d65f03c0 ret
Will
--->8
Will Deacon (2):
preempt: Move PREEMPT_NEED_RESCHED definition into arch code
arm64: preempt: Provide our own implementation of asm/preempt.h
arch/arm64/include/asm/Kbuild | 1 -
arch/arm64/include/asm/preempt.h | 78 ++++++++++++++++++++++++++++++++++++
arch/arm64/include/asm/thread_info.h | 13 +++++-
arch/s390/include/asm/preempt.h | 2 +
arch/x86/include/asm/preempt.h | 3 ++
include/linux/preempt.h | 3 --
6 files changed, 95 insertions(+), 5 deletions(-)
create mode 100644 arch/arm64/include/asm/preempt.h
--
2.1.4
next reply other threads:[~2018-11-27 19:44 UTC|newest]
Thread overview: 9+ messages / expand[flat|nested] mbox.gz Atom feed top
2018-11-27 19:45 Will Deacon [this message]
2018-11-27 19:45 ` [PATCH 1/2] preempt: Move PREEMPT_NEED_RESCHED definition into arch code Will Deacon
2018-11-27 19:45 ` [PATCH 2/2] arm64: preempt: Provide our own implementation of asm/preempt.h Will Deacon
2018-11-28 15:35 ` Ard Biesheuvel
2018-11-28 16:40 ` Peter Zijlstra
2018-11-28 16:45 ` Ard Biesheuvel
2018-11-28 8:56 ` [PATCH 0/2] arm64: Only call into preempt_schedule() if need_resched() Peter Zijlstra
2018-11-28 9:01 ` Peter Zijlstra
2018-11-28 12:04 ` Will Deacon
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