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https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git
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f7e2cb6d49
Unlike mutex and rw_semaphore, qspinlock has no owner field, so "perf
lock contention --lock-owner" cannot attribute a contended spinlock to
its holder. The waiter-side contention_begin event records that a
spinlock is contended, but not by whom. Firing contended_release in the
holder's context at unlock is the only way to capture the holder of a
contended spinlock.
Combine the contention check, trace call and release in an out-of-line
queued_spin_release_traced() so the compiler need not preserve the lock
pointer in a callee-saved register across the call.
The check in queued_spin_unlock() is paid on every unlock, even while
the tracepoint is disabled: a static-branch NOP on x86_64, and a few
more instructions to manage a stack frame elsewhere. Gate it behind
CONFIG_QUEUED_SPINLOCKS_TRACE_CONTENDED_RELEASE (default n) so nobody
pays for a tracepoint they do not use. Sleeping locks fire
contended_release regardless.
On x86 this generic path is used only with PARAVIRT_SPINLOCKS=n (e.g.
defconfig). PARAVIRT_SPINLOCKS=y kernels keep the paravirt static_call
unlock and are wired up separately.
All below are with the QUEUED_SPINLOCKS_TRACE_CONTENDED_RELEASE option
enabled.
_raw_spin_unlock(), x86_64 defconfig, GCC 11, tracepoint compiled in but
disabled. The unlock is the single 'movb'. The only instruction added to
the executed path is the 2-byte static-branch NOP. The CALL to the
traced helper and the JMP back are emitted out of line and are reached
only once the static branch is patched on:
endbr64 ; 4 bytes
xchg %ax,%ax ; 2 static-branch NOP
; (added)
movb $0x0,(%rdi) ; 3 unlock (single store)
A: decl %gs:__preempt_count ; 7
je B ; 2
jmp __x86_return_thunk ; 5
call queued_spin_release_traced ; 5 out of line, reached
; only when the
; tracepoint is on
jmp A ; 2 (added)
B: call __SCT__preempt_schedule ; 5
jmp __x86_return_thunk ; 5
Baseline is the same stream without the NOP and the out-of-line
CALL/JMP: 31 bytes vs 40 (+9 bytes).
Binary size impact on x86_64, defconfig: +680 bytes (+0.00%), since all
standard configs out-of-line unlock. Architectures with inlined unlock
(s390 (always), csky and loongarch (both when !PREEMPTION)) will see a
bigger increase in binary size.
On the same path (x86_64, PARAVIRT_SPINLOCKS=n) with the tracepoint
disabled, a _raw_spin_unlock()-heavy nginx workload [1] shows no
measurable difference between baseline and patched kernels in
throughput, latency, cycles, instructions, IPC, or L1 instruction-cache
misses (kernel and total): all deltas stay within run-to-run noise.
Unlike x86, on arm64 the frame setup code (STP, MOV and LDP) lands on
the executed path in addition to static-branch NOP. Binary size impact
on arm64, defconfig: +932 bytes (+0.00%).
The _raw_spin_unlock()-heavy nginx workload reflects the larger hot
path: L1 instruction-cache misses rise ~1.4% (kernel and total) and
instruction count ~0.4%, consistent with the per-unlock frame.
cpu_cycles, throughput and latency show no measurable change and are
within run-to-run noise.
Architectures with fully custom qspinlock implementations (e.g.
PowerPC) are not covered by this change.
[1]: https://lore.kernel.org/all/aiphFXe_TPNPxZ_n@shell.ilvokhin.com/
Signed-off-by: Dmitry Ilvokhin <d@ilvokhin.com>
Signed-off-by: Peter Zijlstra (Intel) <peterz@infradead.org>
Acked-by: Juergen Gross <jgross@suse.com>
Link: https://patch.msgid.link/0d998e22a0c595f670cfc6725bb683323aced5cb.1785778551.git.d@ilvokhin.com
282 lines
5.7 KiB
Plaintext
282 lines
5.7 KiB
Plaintext
# SPDX-License-Identifier: GPL-2.0-only
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#
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# The ARCH_INLINE foo is necessary because select ignores "depends on"
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#
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config ARCH_INLINE_SPIN_TRYLOCK
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bool
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config ARCH_INLINE_SPIN_TRYLOCK_BH
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bool
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config ARCH_INLINE_SPIN_LOCK
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bool
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config ARCH_INLINE_SPIN_LOCK_BH
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bool
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config ARCH_INLINE_SPIN_LOCK_IRQ
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bool
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config ARCH_INLINE_SPIN_LOCK_IRQSAVE
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bool
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config ARCH_INLINE_SPIN_UNLOCK
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bool
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config ARCH_INLINE_SPIN_UNLOCK_BH
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bool
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config ARCH_INLINE_SPIN_UNLOCK_IRQ
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bool
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config ARCH_INLINE_SPIN_UNLOCK_IRQRESTORE
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bool
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config ARCH_INLINE_READ_TRYLOCK
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bool
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config ARCH_INLINE_READ_LOCK
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bool
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config ARCH_INLINE_READ_LOCK_BH
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bool
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config ARCH_INLINE_READ_LOCK_IRQ
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bool
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config ARCH_INLINE_READ_LOCK_IRQSAVE
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bool
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config ARCH_INLINE_READ_UNLOCK
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bool
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config ARCH_INLINE_READ_UNLOCK_BH
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bool
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config ARCH_INLINE_READ_UNLOCK_IRQ
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bool
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config ARCH_INLINE_READ_UNLOCK_IRQRESTORE
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bool
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config ARCH_INLINE_WRITE_TRYLOCK
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bool
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config ARCH_INLINE_WRITE_LOCK
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bool
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config ARCH_INLINE_WRITE_LOCK_BH
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bool
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config ARCH_INLINE_WRITE_LOCK_IRQ
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bool
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config ARCH_INLINE_WRITE_LOCK_IRQSAVE
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bool
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config ARCH_INLINE_WRITE_UNLOCK
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bool
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config ARCH_INLINE_WRITE_UNLOCK_BH
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bool
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config ARCH_INLINE_WRITE_UNLOCK_IRQ
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bool
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config ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
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bool
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config UNINLINE_SPIN_UNLOCK
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bool
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#
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# lock_* functions are inlined when:
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# - DEBUG_SPINLOCK=n and GENERIC_LOCKBREAK=n and ARCH_INLINE_*LOCK=y
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#
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# trylock_* functions are inlined when:
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# - DEBUG_SPINLOCK=n and ARCH_INLINE_*LOCK=y
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#
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# unlock and unlock_irq functions are inlined when:
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# - DEBUG_SPINLOCK=n and ARCH_INLINE_*LOCK=y
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# or
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# - DEBUG_SPINLOCK=n and PREEMPTION=n
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#
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# unlock_bh and unlock_irqrestore functions are inlined when:
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# - DEBUG_SPINLOCK=n and ARCH_INLINE_*LOCK=y
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#
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if !DEBUG_SPINLOCK
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config INLINE_SPIN_TRYLOCK
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def_bool y
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depends on ARCH_INLINE_SPIN_TRYLOCK
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config INLINE_SPIN_TRYLOCK_BH
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def_bool y
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depends on ARCH_INLINE_SPIN_TRYLOCK_BH
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config INLINE_SPIN_LOCK
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_SPIN_LOCK
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config INLINE_SPIN_LOCK_BH
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_SPIN_LOCK_BH
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config INLINE_SPIN_LOCK_IRQ
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_SPIN_LOCK_IRQ
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config INLINE_SPIN_LOCK_IRQSAVE
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_SPIN_LOCK_IRQSAVE
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config INLINE_SPIN_UNLOCK_BH
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def_bool y
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depends on ARCH_INLINE_SPIN_UNLOCK_BH
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config INLINE_SPIN_UNLOCK_IRQ
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def_bool y
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depends on !PREEMPTION || ARCH_INLINE_SPIN_UNLOCK_IRQ
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config INLINE_SPIN_UNLOCK_IRQRESTORE
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def_bool y
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depends on ARCH_INLINE_SPIN_UNLOCK_IRQRESTORE
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config INLINE_READ_TRYLOCK
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def_bool y
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depends on ARCH_INLINE_READ_TRYLOCK
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config INLINE_READ_LOCK
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_READ_LOCK
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config INLINE_READ_LOCK_BH
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_READ_LOCK_BH
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config INLINE_READ_LOCK_IRQ
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_READ_LOCK_IRQ
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config INLINE_READ_LOCK_IRQSAVE
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_READ_LOCK_IRQSAVE
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config INLINE_READ_UNLOCK
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def_bool y
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depends on !PREEMPTION || ARCH_INLINE_READ_UNLOCK
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config INLINE_READ_UNLOCK_BH
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def_bool y
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depends on ARCH_INLINE_READ_UNLOCK_BH
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config INLINE_READ_UNLOCK_IRQ
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def_bool y
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depends on !PREEMPTION || ARCH_INLINE_READ_UNLOCK_IRQ
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config INLINE_READ_UNLOCK_IRQRESTORE
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def_bool y
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depends on ARCH_INLINE_READ_UNLOCK_IRQRESTORE
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config INLINE_WRITE_TRYLOCK
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def_bool y
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depends on ARCH_INLINE_WRITE_TRYLOCK
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config INLINE_WRITE_LOCK
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_WRITE_LOCK
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config INLINE_WRITE_LOCK_BH
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_WRITE_LOCK_BH
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config INLINE_WRITE_LOCK_IRQ
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_WRITE_LOCK_IRQ
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config INLINE_WRITE_LOCK_IRQSAVE
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def_bool y
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depends on !GENERIC_LOCKBREAK && ARCH_INLINE_WRITE_LOCK_IRQSAVE
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config INLINE_WRITE_UNLOCK
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def_bool y
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depends on !PREEMPTION || ARCH_INLINE_WRITE_UNLOCK
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config INLINE_WRITE_UNLOCK_BH
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def_bool y
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depends on ARCH_INLINE_WRITE_UNLOCK_BH
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config INLINE_WRITE_UNLOCK_IRQ
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def_bool y
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depends on !PREEMPTION || ARCH_INLINE_WRITE_UNLOCK_IRQ
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config INLINE_WRITE_UNLOCK_IRQRESTORE
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def_bool y
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depends on ARCH_INLINE_WRITE_UNLOCK_IRQRESTORE
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endif
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config ARCH_SUPPORTS_ATOMIC_RMW
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bool
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config MUTEX_SPIN_ON_OWNER
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def_bool y
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depends on SMP && ARCH_SUPPORTS_ATOMIC_RMW
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config RWSEM_SPIN_ON_OWNER
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def_bool y
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depends on SMP && ARCH_SUPPORTS_ATOMIC_RMW
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config LOCK_SPIN_ON_OWNER
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def_bool y
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depends on MUTEX_SPIN_ON_OWNER || RWSEM_SPIN_ON_OWNER
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config ARCH_USE_QUEUED_SPINLOCKS
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bool
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config QUEUED_SPINLOCKS
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def_bool y if ARCH_USE_QUEUED_SPINLOCKS
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depends on SMP
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config QUEUED_SPINLOCKS_TRACE_CONTENDED_RELEASE
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bool "Trace contended_release on queued spinlocks"
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depends on QUEUED_SPINLOCKS && TRACEPOINTS
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help
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Fire the lock:contended_release tracepoint when a contended queued
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spinlock is released, so it is possible to attribute a contended
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spinlock to its holder.
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Architectures that can patch the unlock site do this at no cost and
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do not need this option.
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Everywhere else the check is compiled into queued_spin_unlock() and
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a small cost is paid on every unlock even when the tracepoint is
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disabled: a static-branch NOP and possibly a few more instructions
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to manage a stack frame.
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Sleeping locks fire lock:contended_release regardless of this option.
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If unsure, say N.
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config BPF_ARCH_SPINLOCK
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bool
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config ARCH_USE_QUEUED_RWLOCKS
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bool
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config QUEUED_RWLOCKS
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def_bool y if ARCH_USE_QUEUED_RWLOCKS
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depends on SMP && !PREEMPT_RT
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config ARCH_HAS_MMIOWB
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bool
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config MMIOWB
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def_bool y if ARCH_HAS_MMIOWB
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depends on SMP
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