linux-kernel - Re: [PATCH v2] locking: Add __lockfunc to slow path functions

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Message-ID: <c7e4289a-a995-65f2-47fc-054b7e55757d@redhat.com>
Date:   Thu, 11 Aug 2022 14:19:53 -0400
From:   Waiman Long <longman@...hat.com>
To:     Namhyung Kim <namhyung@...nel.org>,
        Peter Zijlstra <peterz@...radead.org>,
        Ingo Molnar <mingo@...nel.org>, Will Deacon <will@...nel.org>
Cc:     Boqun Feng <boqun.feng@...il.com>,
        LKML <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH v2] locking: Add __lockfunc to slow path functions

On 8/10/22 18:03, Namhyung Kim wrote:
> So that we can skip the functions in the perf lock contention and other
> places like /proc/PID/wchan.
>
> Signed-off-by: Namhyung Kim <namhyung@...nel.org>
> ---
> * annotate pv qspinlock functions too
>
>   arch/x86/include/asm/qspinlock_paravirt.h | 13 +++++++------
>   kernel/locking/qrwlock.c                  |  4 ++--
>   kernel/locking/qspinlock.c                |  2 +-
>   kernel/locking/qspinlock_paravirt.h       |  4 ++--
>   4 files changed, 12 insertions(+), 11 deletions(-)
>
> diff --git a/arch/x86/include/asm/qspinlock_paravirt.h b/arch/x86/include/asm/qspinlock_paravirt.h
> index 892fd8c3a6f7..60ece592b220 100644
> --- a/arch/x86/include/asm/qspinlock_paravirt.h
> +++ b/arch/x86/include/asm/qspinlock_paravirt.h
> @@ -12,7 +12,7 @@
>    */
>   #ifdef CONFIG_64BIT
>   
> -PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath);
> +__PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath, ".spinlock.text");
>   #define __pv_queued_spin_unlock	__pv_queued_spin_unlock
>   #define PV_UNLOCK		"__raw_callee_save___pv_queued_spin_unlock"
>   #define PV_UNLOCK_SLOWPATH	"__raw_callee_save___pv_queued_spin_unlock_slowpath"
> @@ -20,9 +20,10 @@ PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath);
>   /*
>    * Optimized assembly version of __raw_callee_save___pv_queued_spin_unlock
>    * which combines the registers saving trunk and the body of the following
> - * C code:
> + * C code.  Note that it puts the code in the .spinlock.text section which
> + * is equivalent to adding __lockfunc in the C code:
>    *
> - * void __pv_queued_spin_unlock(struct qspinlock *lock)
> + * void __lockfunc __pv_queued_spin_unlock(struct qspinlock *lock)
>    * {
>    *	u8 lockval = cmpxchg(&lock->locked, _Q_LOCKED_VAL, 0);
>    *
> @@ -36,7 +37,7 @@ PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock_slowpath);
>    *   rsi = lockval           (second argument)
>    *   rdx = internal variable (set to 0)
>    */
> -asm    (".pushsection .text;"
> +asm    (".pushsection .spinlock.text;"
>   	".globl " PV_UNLOCK ";"
>   	".type " PV_UNLOCK ", @function;"
>   	".align 4,0x90;"
> @@ -65,8 +66,8 @@ asm    (".pushsection .text;"
>   
>   #else /* CONFIG_64BIT */
>   
> -extern void __pv_queued_spin_unlock(struct qspinlock *lock);
> -PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock);
> +extern void __lockfunc __pv_queued_spin_unlock(struct qspinlock *lock);
> +__PV_CALLEE_SAVE_REGS_THUNK(__pv_queued_spin_unlock, ".spinlock.text");
>   
>   #endif /* CONFIG_64BIT */
>   #endif
> diff --git a/kernel/locking/qrwlock.c b/kernel/locking/qrwlock.c
> index 2e1600906c9f..d2ef312a8611 100644
> --- a/kernel/locking/qrwlock.c
> +++ b/kernel/locking/qrwlock.c
> @@ -18,7 +18,7 @@
>    * queued_read_lock_slowpath - acquire read lock of a queued rwlock
>    * @lock: Pointer to queued rwlock structure
>    */
> -void queued_read_lock_slowpath(struct qrwlock *lock)
> +void __lockfunc queued_read_lock_slowpath(struct qrwlock *lock)
>   {
>   	/*
>   	 * Readers come here when they cannot get the lock without waiting
> @@ -63,7 +63,7 @@ EXPORT_SYMBOL(queued_read_lock_slowpath);
>    * queued_write_lock_slowpath - acquire write lock of a queued rwlock
>    * @lock : Pointer to queued rwlock structure
>    */
> -void queued_write_lock_slowpath(struct qrwlock *lock)
> +void __lockfunc queued_write_lock_slowpath(struct qrwlock *lock)
>   {
>   	int cnts;
>   
> diff --git a/kernel/locking/qspinlock.c b/kernel/locking/qspinlock.c
> index 65a9a10caa6f..2b23378775fe 100644
> --- a/kernel/locking/qspinlock.c
> +++ b/kernel/locking/qspinlock.c
> @@ -313,7 +313,7 @@ static __always_inline u32  __pv_wait_head_or_lock(struct qspinlock *lock,
>    * contended             :    (*,x,y) +--> (*,0,0) ---> (*,0,1) -'  :
>    *   queue               :         ^--'                             :
>    */
> -void queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
> +void __lockfunc queued_spin_lock_slowpath(struct qspinlock *lock, u32 val)
>   {
>   	struct mcs_spinlock *prev, *next, *node;
>   	u32 old, tail;
> diff --git a/kernel/locking/qspinlock_paravirt.h b/kernel/locking/qspinlock_paravirt.h
> index e84d21aa0722..6afc249ce697 100644
> --- a/kernel/locking/qspinlock_paravirt.h
> +++ b/kernel/locking/qspinlock_paravirt.h
> @@ -489,7 +489,7 @@ pv_wait_head_or_lock(struct qspinlock *lock, struct mcs_spinlock *node)
>    * PV versions of the unlock fastpath and slowpath functions to be used
>    * instead of queued_spin_unlock().
>    */
> -__visible void
> +__visible __lockfunc void
>   __pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
>   {
>   	struct pv_node *node;
> @@ -544,7 +544,7 @@ __pv_queued_spin_unlock_slowpath(struct qspinlock *lock, u8 locked)
>   #include <asm/qspinlock_paravirt.h>
>   
>   #ifndef __pv_queued_spin_unlock
> -__visible void __pv_queued_spin_unlock(struct qspinlock *lock)
> +__visible __lockfunc void __pv_queued_spin_unlock(struct qspinlock *lock)
>   {
>   	u8 locked;
>   
Acked-by: Waiman Long <longman@...hat.com>