On Wed, May 29, 2024 at 9:03 PM Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> wrote: > > Hi Guo, > > On Wed, May 29, 2024 at 11:24 AM Guo Ren <guoren@xxxxxxxxxx> wrote: > > > > On Tue, May 28, 2024 at 11:18 PM Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> wrote: > > > > > > In order to produce a generic kernel, a user can select > > > CONFIG_QUEUED_SPINLOCKS which will fallback at runtime to the ticket > > > spinlock implementation if Zabha is not present. > > > > > > Note that we can't use alternatives here because the discovery of > > > extensions is done too late and we need to start with the qspinlock > > > implementation because the ticket spinlock implementation would pollute > > > the spinlock value, so let's use static keys. > > > > > > This is largely based on Guo's work and Leonardo reviews at [1]. > > > > > > Link: https://lore.kernel.org/linux-riscv/20231225125847.2778638-1-guoren@xxxxxxxxxx/ [1] > > > Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> > > > --- > > > .../locking/queued-spinlocks/arch-support.txt | 2 +- > > > arch/riscv/Kconfig | 1 + > > > arch/riscv/include/asm/Kbuild | 4 +- > > > arch/riscv/include/asm/spinlock.h | 39 +++++++++++++++++++ > > > arch/riscv/kernel/setup.c | 18 +++++++++ > > > include/asm-generic/qspinlock.h | 2 + > > > include/asm-generic/ticket_spinlock.h | 2 + > > > 7 files changed, 66 insertions(+), 2 deletions(-) > > > create mode 100644 arch/riscv/include/asm/spinlock.h > > > > > > diff --git a/Documentation/features/locking/queued-spinlocks/arch-support.txt b/Documentation/features/locking/queued-spinlocks/arch-support.txt > > > index 22f2990392ff..cf26042480e2 100644 > > > --- a/Documentation/features/locking/queued-spinlocks/arch-support.txt > > > +++ b/Documentation/features/locking/queued-spinlocks/arch-support.txt > > > @@ -20,7 +20,7 @@ > > > | openrisc: | ok | > > > | parisc: | TODO | > > > | powerpc: | ok | > > > - | riscv: | TODO | > > > + | riscv: | ok | > > > | s390: | TODO | > > > | sh: | TODO | > > > | sparc: | ok | > > > diff --git a/arch/riscv/Kconfig b/arch/riscv/Kconfig > > > index 184a9edb04e0..ccf1703edeb9 100644 > > > --- a/arch/riscv/Kconfig > > > +++ b/arch/riscv/Kconfig > > > @@ -59,6 +59,7 @@ config RISCV > > > select ARCH_SUPPORTS_SHADOW_CALL_STACK if HAVE_SHADOW_CALL_STACK > > > select ARCH_USE_MEMTEST > > > select ARCH_USE_QUEUED_RWLOCKS > > > + select ARCH_USE_QUEUED_SPINLOCKS if TOOLCHAIN_HAS_ZABHA > > Using qspinlock or not depends on real hardware capabilities, not the > > compiler flag. That's why I introduced combo-spinlock, ticket-spinlock > > & qspinlock three Kconfigs, and the combo-spinlock would compat all > > hardware platforms but waste some qspinlock code size. > > You're right, and I think your comment matches what Conor mentioned > about the lack of clarity with some extensions: TOOLCHAIN_HAS_ZABHA > will allow a platform with Zabha capability to use qspinlocks. But if > the hardware does not, it will fallback to the ticket spinlocks. > > But I agree that looking at the config alone may be misleading, even > though it will work as expected at runtime. So I agree with you: > unless anyone is strongly against the combo spinlocks, I will do what > you suggest and add them. The problem with the v12 combo-spinlock is using a static_branch instead of the full ALTERNATIVE. Frankly, that's a bad example that costs more code space. I found that your cmpxchg32/64 also uses a condition branch, which has a similar problem, right? Anyway, your patch series inspired me to update the v13 combo-spinlock. My plan is: 1. Separate native-qspinlock out of paravirt-qspinlock. 2. Re-design an ALTERNATIVE(asm) code instead of static_branch generic ticket-lock or qspinlock. What do you think? > > Thanks again for your initial work, > > Alex > > > > > > select ARCH_USES_CFI_TRAPS if CFI_CLANG > > > select ARCH_WANT_BATCHED_UNMAP_TLB_FLUSH if SMP && MMU > > > select ARCH_WANT_DEFAULT_TOPDOWN_MMAP_LAYOUT if MMU > > > diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild > > > index 504f8b7e72d4..ad72f2bd4cc9 100644 > > > --- a/arch/riscv/include/asm/Kbuild > > > +++ b/arch/riscv/include/asm/Kbuild > > > @@ -2,10 +2,12 @@ > > > generic-y += early_ioremap.h > > > generic-y += flat.h > > > generic-y += kvm_para.h > > > +generic-y += mcs_spinlock.h > > > generic-y += parport.h > > > -generic-y += spinlock.h > > > generic-y += spinlock_types.h > > > +generic-y += ticket_spinlock.h > > > generic-y += qrwlock.h > > > generic-y += qrwlock_types.h > > > +generic-y += qspinlock.h > > > generic-y += user.h > > > generic-y += vmlinux.lds.h > > > diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h > > > new file mode 100644 > > > index 000000000000..e00429ac20ed > > > --- /dev/null > > > +++ b/arch/riscv/include/asm/spinlock.h > > > @@ -0,0 +1,39 @@ > > > +/* SPDX-License-Identifier: GPL-2.0 */ > > > + > > > +#ifndef __ASM_RISCV_SPINLOCK_H > > > +#define __ASM_RISCV_SPINLOCK_H > > > + > > > +#ifdef CONFIG_QUEUED_SPINLOCKS > > > +#define _Q_PENDING_LOOPS (1 << 9) > > > + > > > +#define __no_arch_spinlock_redefine > > > +#include <asm/ticket_spinlock.h> > > > +#include <asm/qspinlock.h> > > > +#include <asm/alternative.h> > > > + > > > +DECLARE_STATIC_KEY_TRUE(qspinlock_key); > > > + > > > +#define SPINLOCK_BASE_DECLARE(op, type, type_lock) \ > > > +static __always_inline type arch_spin_##op(type_lock lock) \ > > > +{ \ > > > + if (static_branch_unlikely(&qspinlock_key)) \ > > > + return queued_spin_##op(lock); \ > > > + return ticket_spin_##op(lock); \ > > > +} > > > + > > > +SPINLOCK_BASE_DECLARE(lock, void, arch_spinlock_t *) > > > +SPINLOCK_BASE_DECLARE(unlock, void, arch_spinlock_t *) > > > +SPINLOCK_BASE_DECLARE(is_locked, int, arch_spinlock_t *) > > > +SPINLOCK_BASE_DECLARE(is_contended, int, arch_spinlock_t *) > > > +SPINLOCK_BASE_DECLARE(trylock, bool, arch_spinlock_t *) > > > +SPINLOCK_BASE_DECLARE(value_unlocked, int, arch_spinlock_t) > > > + > > > +#else > > > + > > > +#include <asm/ticket_spinlock.h> > > > + > > > +#endif > > > + > > > +#include <asm/qrwlock.h> > > > + > > > +#endif /* __ASM_RISCV_SPINLOCK_H */ > > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > > > index 4f73c0ae44b2..31ce75522fd4 100644 > > > --- a/arch/riscv/kernel/setup.c > > > +++ b/arch/riscv/kernel/setup.c > > > @@ -244,6 +244,23 @@ static void __init parse_dtb(void) > > > #endif > > > } > > > > > > +DEFINE_STATIC_KEY_TRUE(qspinlock_key); > > > +EXPORT_SYMBOL(qspinlock_key); > > > + > > > +static void __init riscv_spinlock_init(void) > > > +{ > > > + asm goto(ALTERNATIVE("nop", "j %[qspinlock]", 0, RISCV_ISA_EXT_ZABHA, 1) > > > + : : : : qspinlock); > > > + > > > + static_branch_disable(&qspinlock_key); > > > + pr_info("Ticket spinlock: enabled\n"); > > > + > > > + return; > > > + > > > +qspinlock: > > > + pr_info("Queued spinlock: enabled\n"); > > > +} > > > + > > > extern void __init init_rt_signal_env(void); > > > > > > void __init setup_arch(char **cmdline_p) > > > @@ -295,6 +312,7 @@ void __init setup_arch(char **cmdline_p) > > > riscv_set_dma_cache_alignment(); > > > > > > riscv_user_isa_enable(); > > > + riscv_spinlock_init(); > > > } > > > > > > bool arch_cpu_is_hotpluggable(int cpu) > > > diff --git a/include/asm-generic/qspinlock.h b/include/asm-generic/qspinlock.h > > > index 0655aa5b57b2..bf47cca2c375 100644 > > > --- a/include/asm-generic/qspinlock.h > > > +++ b/include/asm-generic/qspinlock.h > > > @@ -136,6 +136,7 @@ static __always_inline bool virt_spin_lock(struct qspinlock *lock) > > > } > > > #endif > > > > > > +#ifndef __no_arch_spinlock_redefine > > > /* > > > * Remapping spinlock architecture specific functions to the corresponding > > > * queued spinlock functions. > > > @@ -146,5 +147,6 @@ static __always_inline bool virt_spin_lock(struct qspinlock *lock) > > > #define arch_spin_lock(l) queued_spin_lock(l) > > > #define arch_spin_trylock(l) queued_spin_trylock(l) > > > #define arch_spin_unlock(l) queued_spin_unlock(l) > > > +#endif > > > > > > #endif /* __ASM_GENERIC_QSPINLOCK_H */ > > > diff --git a/include/asm-generic/ticket_spinlock.h b/include/asm-generic/ticket_spinlock.h > > > index cfcff22b37b3..325779970d8a 100644 > > > --- a/include/asm-generic/ticket_spinlock.h > > > +++ b/include/asm-generic/ticket_spinlock.h > > > @@ -89,6 +89,7 @@ static __always_inline int ticket_spin_is_contended(arch_spinlock_t *lock) > > > return (s16)((val >> 16) - (val & 0xffff)) > 1; > > > } > > > > > > +#ifndef __no_arch_spinlock_redefine > > > /* > > > * Remapping spinlock architecture specific functions to the corresponding > > > * ticket spinlock functions. > > > @@ -99,5 +100,6 @@ static __always_inline int ticket_spin_is_contended(arch_spinlock_t *lock) > > > #define arch_spin_lock(l) ticket_spin_lock(l) > > > #define arch_spin_trylock(l) ticket_spin_trylock(l) > > > #define arch_spin_unlock(l) ticket_spin_unlock(l) > > > +#endif > > > > > > #endif /* __ASM_GENERIC_TICKET_SPINLOCK_H */ > > > -- > > > 2.39.2 > > > > > > > > > -- > > Best Regards > > Guo Ren -- Best Regards Guo Ren
