Re: [PATCH V11 06/17] riscv: qspinlock: Introduce combo spinlock

[Leonardo Bras <leobras@redhat.com>]

On Wed, Sep 13, 2023 at 05:37:01PM -0300, Leonardo Bras wrote:
> On Sun, Sep 10, 2023 at 07:06:23AM -0400, Guo Ren wrote:
> > On Sun, Sep 10, 2023 at 04:29:00AM -0400, guoren@kernel.org wrote:
> > > From: Guo Ren <guoren@linux.alibaba.com>
> > > 
> > > Combo spinlock could support queued and ticket in one Linux Image and
> > > select them during boot time via errata mechanism. Here is the func
> > > size (Bytes) comparison table below:
> > > 
> > > TYPE			: COMBO | TICKET | QUEUED
> > > arch_spin_lock		: 106	| 60     | 50
> > > arch_spin_unlock	: 54    | 36     | 26
> > > arch_spin_trylock	: 110   | 72     | 54
> > > arch_spin_is_locked	: 48    | 34     | 20
> > > arch_spin_is_contended	: 56    | 40     | 24
> > > rch_spin_value_unlocked	: 48    | 34     | 24
> > > 
> > > One example of disassemble combo arch_spin_unlock:
> > >    0xffffffff8000409c <+14>:    nop                # detour slot
> > >    0xffffffff800040a0 <+18>:    fence   rw,w       # queued spinlock start
> > >    0xffffffff800040a4 <+22>:    sb      zero,0(a4) # queued spinlock end
> > >    0xffffffff800040a8 <+26>:    ld      s0,8(sp)
> > >    0xffffffff800040aa <+28>:    addi    sp,sp,16
> > >    0xffffffff800040ac <+30>:    ret
> > >    0xffffffff800040ae <+32>:    lw      a5,0(a4)   # ticket spinlock start
> > >    0xffffffff800040b0 <+34>:    sext.w  a5,a5
> > >    0xffffffff800040b2 <+36>:    fence   rw,w
> > >    0xffffffff800040b6 <+40>:    addiw   a5,a5,1
> > >    0xffffffff800040b8 <+42>:    slli    a5,a5,0x30
> > >    0xffffffff800040ba <+44>:    srli    a5,a5,0x30
> > >    0xffffffff800040bc <+46>:    sh      a5,0(a4)   # ticket spinlock end
> > >    0xffffffff800040c0 <+50>:    ld      s0,8(sp)
> > >    0xffffffff800040c2 <+52>:    addi    sp,sp,16
> > >    0xffffffff800040c4 <+54>:    ret
> > > 
> > > The qspinlock is smaller and faster than ticket-lock when all are in
> > > fast-path, and combo spinlock could provide a compatible Linux Image
> > > for different micro-arch design (weak/strict fwd guarantee LR/SC)
> > > processors.
> > > 
> > > Signed-off-by: Guo Ren <guoren@kernel.org>
> > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com>
> > > ---
> > >  arch/riscv/Kconfig                |  9 +++-
> > >  arch/riscv/include/asm/spinlock.h | 78 ++++++++++++++++++++++++++++++-
> > >  arch/riscv/kernel/setup.c         | 14 ++++++
> > >  3 files changed, 98 insertions(+), 3 deletions(-)
> > > 
> > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig
> > > index 7f39bfc75744..4bcff2860f48 100644
> > > --- a/arch/riscv/Kconfig
> > > +++ b/arch/riscv/Kconfig
> > > @@ -473,7 +473,7 @@ config NODES_SHIFT
> > >  
> > >  choice
> > >  	prompt "RISC-V spinlock type"
> > > -	default RISCV_TICKET_SPINLOCKS
> > > +	default RISCV_COMBO_SPINLOCKS
> > >  
> > >  config RISCV_TICKET_SPINLOCKS
> > >  	bool "Using ticket spinlock"
> > > @@ -485,6 +485,13 @@ config RISCV_QUEUED_SPINLOCKS
> > >  	help
> > >  	  Make sure your micro arch LL/SC has a strong forward progress guarantee.
> > >  	  Otherwise, stay at ticket-lock.
> > > +
> > > +config RISCV_COMBO_SPINLOCKS
> > > +	bool "Using combo spinlock"
> > > +	depends on SMP && MMU
> > > +	select ARCH_USE_QUEUED_SPINLOCKS
> > > +	help
> > > +	  Select queued spinlock or ticket-lock via errata.
> > >  endchoice
> > >  
> > >  config RISCV_ALTERNATIVE
> > > diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h
> > > index c644a92d4548..8ea0fee80652 100644
> > > --- a/arch/riscv/include/asm/spinlock.h
> > > +++ b/arch/riscv/include/asm/spinlock.h
> > > @@ -7,11 +7,85 @@
> > >  #define _Q_PENDING_LOOPS	(1 << 9)
> > >  #endif
> > >  
> > > +#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
> > > +#include <asm-generic/ticket_spinlock.h>
> > > +
> > > +#undef arch_spin_is_locked
> > > +#undef arch_spin_is_contended
> > > +#undef arch_spin_value_unlocked
> > > +#undef arch_spin_lock
> > > +#undef arch_spin_trylock
> > > +#undef arch_spin_unlock
> > > +
> > > +#include <asm-generic/qspinlock.h>
> > > +#include <linux/jump_label.h>
> > > +
> > > +#undef arch_spin_is_locked
> > > +#undef arch_spin_is_contended
> > > +#undef arch_spin_value_unlocked
> > > +#undef arch_spin_lock
> > > +#undef arch_spin_trylock
> > > +#undef arch_spin_unlock
> > Sorry, I forgot __no_arch_spinlock_redefine advice here. I would add it in v12.
> > https://lore.kernel.org/linux-riscv/4cc7113a-0e4e-763a-cba2-7963bcd26c7a@redhat.com/
> > 
> 
> Please check a reply to a previous patch I sent earlier: I think these 
> #undef can be avoided.
>  
> > > +
> > > +DECLARE_STATIC_KEY_TRUE(combo_qspinlock_key);
> > > +
> > > +static __always_inline void arch_spin_lock(arch_spinlock_t *lock)
> > > +{
> > > +	if (static_branch_likely(&combo_qspinlock_key))
> > > +		queued_spin_lock(lock);
> > > +	else
> > > +		ticket_spin_lock(lock);
> > > +}
> > > +
> > > +static __always_inline bool arch_spin_trylock(arch_spinlock_t *lock)
> > > +{
> > > +	if (static_branch_likely(&combo_qspinlock_key))
> > > +		return queued_spin_trylock(lock);
> > > +	else
> > > +		return ticket_spin_trylock(lock);
> > > +}
> > > +
> > > +static __always_inline void arch_spin_unlock(arch_spinlock_t *lock)
> > > +{
> > > +	if (static_branch_likely(&combo_qspinlock_key))
> > > +		queued_spin_unlock(lock);
> > > +	else
> > > +		ticket_spin_unlock(lock);
> > > +}
> > > +
> > > +static __always_inline int arch_spin_value_unlocked(arch_spinlock_t lock)
> > > +{
> > > +	if (static_branch_likely(&combo_qspinlock_key))
> > > +		return queued_spin_value_unlocked(lock);
> > > +	else
> > > +		return ticket_spin_value_unlocked(lock);
> > > +}
> > > +
> > > +static __always_inline int arch_spin_is_locked(arch_spinlock_t *lock)
> > > +{
> > > +	if (static_branch_likely(&combo_qspinlock_key))
> > > +		return queued_spin_is_locked(lock);
> > > +	else
> > > +		return ticket_spin_is_locked(lock);
> > > +}
> > > +
> > > +static __always_inline int arch_spin_is_contended(arch_spinlock_t *lock)
> > > +{
> > > +	if (static_branch_likely(&combo_qspinlock_key))
> > > +		return queued_spin_is_contended(lock);
> > > +	else
> > > +		return ticket_spin_is_contended(lock);
> > > +}
> > > +#else /* CONFIG_RISCV_COMBO_SPINLOCKS */
> > > +

Also, those functions all reproduce the same behavior, so maybe it would be 
better to keep that behavior in a macro such as:

#define COMBO_SPINLOCK_DECLARE(f) 					\
static __always_inline int arch_spin_ ## f(arch_spinlock_t *lock) 	\
{									\
	if (static_branch_likely(&combo_qspinlock_key))			\
		return queued_spin_ ## f(lock);				\
	else								\
		return ticket_spin_ ## f(lock);				\
}

COMBO_SPINLOCK_DECLARE(lock)
COMBO_SPINLOCK_DECLARE(trylock)
COMBO_SPINLOCK_DECLARE(unlock)
COMBO_SPINLOCK_DECLARE(value_unlocked)
COMBO_SPINLOCK_DECLARE(is_locked)
COMBO_SPINLOCK_DECLARE(is_contended)

Does that make sense?

Thanks!
Leo


> > >  #ifdef CONFIG_QUEUED_SPINLOCKS
> > >  #include <asm/qspinlock.h>
> > > -#include <asm/qrwlock.h>
> > >  #else
> > > -#include <asm-generic/spinlock.h>
> > > +#include <asm-generic/ticket_spinlock.h>
> > >  #endif
> > >  
> > > +#endif /* CONFIG_RISCV_COMBO_SPINLOCKS */
> > > +
> > > +#include <asm/qrwlock.h>
> > > +
> > >  #endif /* __ASM_RISCV_SPINLOCK_H */
> > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c
> > > index 32c2e1eb71bd..a447cf360a18 100644
> > > --- a/arch/riscv/kernel/setup.c
> > > +++ b/arch/riscv/kernel/setup.c
> > > @@ -269,6 +269,18 @@ static void __init parse_dtb(void)
> > >  #endif
> > >  }
> > >  
> > > +#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
> > > +DEFINE_STATIC_KEY_TRUE(combo_qspinlock_key);
> > > +EXPORT_SYMBOL(combo_qspinlock_key);
> > > +#endif
> > > +
> > > +static void __init riscv_spinlock_init(void)
> > > +{
> > > +#ifdef CONFIG_RISCV_COMBO_SPINLOCKS
> > > +	static_branch_disable(&combo_qspinlock_key);
> > > +#endif
> > > +}
> > > +
> > >  extern void __init init_rt_signal_env(void);
> > >  
> > >  void __init setup_arch(char **cmdline_p)
> > > @@ -317,6 +329,8 @@ void __init setup_arch(char **cmdline_p)
> > >  	    riscv_isa_extension_available(NULL, ZICBOM))
> > >  		riscv_noncoherent_supported();
> > >  	riscv_set_dma_cache_alignment();
> > > +
> > > +	riscv_spinlock_init();
> > >  }
> > >  
> > >  static int __init topology_init(void)
> > > -- 
> > > 2.36.1
> > > 
> > > 
> > > _______________________________________________
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> > > linux-riscv@lists.infradead.org
> > > http://lists.infradead.org/mailman/listinfo/linux-riscv
> > > 
> >