(I missed a bunch of comments addressed here) On Wed, Jul 31, 2024 at 5:29 PM Andrew Jones <ajones@xxxxxxxxxxxxxxxx> wrote: > > On Wed, Jul 31, 2024 at 09:24:05AM GMT, Alexandre Ghiti wrote: > > In order to produce a generic kernel, a user can select > > CONFIG_COMBO_SPINLOCKS which will fallback at runtime to the ticket > > spinlock implementation if Zabha or Ziccrse are 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: Guo Ren <guoren@xxxxxxxxxx> > > Signed-off-by: Alexandre Ghiti <alexghiti@xxxxxxxxxxxx> > > --- > > .../locking/queued-spinlocks/arch-support.txt | 2 +- > > arch/riscv/Kconfig | 29 +++++++++++++ > > arch/riscv/include/asm/Kbuild | 4 +- > > arch/riscv/include/asm/spinlock.h | 43 +++++++++++++++++++ > > arch/riscv/kernel/setup.c | 38 ++++++++++++++++ > > include/asm-generic/qspinlock.h | 2 + > > include/asm-generic/ticket_spinlock.h | 2 + > > 7 files changed, 118 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 ef55ab94027e..c9ff8081efc1 100644 > > --- a/arch/riscv/Kconfig > > +++ b/arch/riscv/Kconfig > > @@ -79,6 +79,7 @@ config RISCV > > select ARCH_WANT_OPTIMIZE_HUGETLB_VMEMMAP > > select ARCH_WANTS_NO_INSTR > > select ARCH_WANTS_THP_SWAP if HAVE_ARCH_TRANSPARENT_HUGEPAGE > > + select ARCH_WEAK_RELEASE_ACQUIRE if ARCH_USE_QUEUED_SPINLOCKS > > Why do we need this? Also, we presumably would prefer not to have it > when we end up using ticket spinlocks when combo spinlocks is selected. > Is there no way to avoid it? > > > select BINFMT_FLAT_NO_DATA_START_OFFSET if !MMU > > select BUILDTIME_TABLE_SORT if MMU > > select CLINT_TIMER if RISCV_M_MODE > > @@ -488,6 +489,34 @@ config NODES_SHIFT > > Specify the maximum number of NUMA Nodes available on the target > > system. Increases memory reserved to accommodate various tables. > > > > +choice > > + prompt "RISC-V spinlock type" > > + default RISCV_COMBO_SPINLOCKS > > + > > +config RISCV_TICKET_SPINLOCKS > > + bool "Using ticket spinlock" > > + > > +config RISCV_QUEUED_SPINLOCKS > > + bool "Using queued spinlock" > > + depends on SMP && MMU && NONPORTABLE > > + select ARCH_USE_QUEUED_SPINLOCKS > > + help > > + The queued spinlock implementation requires the forward progress > > + guarantee of cmpxchg()/xchg() atomic operations: CAS with Zabha or > > + LR/SC with Ziccrse provide such guarantee. > > + > > + Select this if and only if Zabha or Ziccrse is available on your > > + platform. > > Maybe some text recommending combo spinlocks here? As it stands it sounds > like enabling queued spinlocks is a bad idea for anybody that doesn't know > what platforms will run the kernel they're building, which is all distros. > > > + > > +config RISCV_COMBO_SPINLOCKS > > + bool "Using combo spinlock" > > + depends on SMP && MMU > > + select ARCH_USE_QUEUED_SPINLOCKS > > + help > > + Embed both queued spinlock and ticket lock so that the spinlock > > + implementation can be chosen at runtime. > > nit: Add a blank line here > > > +endchoice > > + > > config RISCV_ALTERNATIVE > > bool > > depends on !XIP_KERNEL > > diff --git a/arch/riscv/include/asm/Kbuild b/arch/riscv/include/asm/Kbuild > > index 5c589770f2a8..1c2618c964f0 100644 > > --- a/arch/riscv/include/asm/Kbuild > > +++ b/arch/riscv/include/asm/Kbuild > > @@ -5,10 +5,12 @@ syscall-y += syscall_table_64.h > > 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..503aef31db83 > > --- /dev/null > > +++ b/arch/riscv/include/asm/spinlock.h > > @@ -0,0 +1,43 @@ > > +/* SPDX-License-Identifier: GPL-2.0 */ > > + > > +#ifndef __ASM_RISCV_SPINLOCK_H > > +#define __ASM_RISCV_SPINLOCK_H > > + > > +#ifdef CONFIG_RISCV_COMBO_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> > > We need asm/jump_label.h instead of asm/alternative.h, but... Done > > > + > > +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); \ > > +} > > ...do you know what impact this inlined static key check has on the > kernel size? > > Actually, why not use ALTERNATIVE with any nonzero cpufeature value. > Then add code to riscv_cpufeature_patch_check() to return true when > qspinlocks should be enabled (based on the value of some global set > during riscv_spinlock_init)? > > > + > > +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) > > + > > +#elif defined(CONFIG_RISCV_QUEUED_SPINLOCKS) > > + > > +#include <asm/qspinlock.h> > > + > > +#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 a2cde65b69e9..b811fa331982 100644 > > --- a/arch/riscv/kernel/setup.c > > +++ b/arch/riscv/kernel/setup.c > > @@ -244,6 +244,43 @@ static void __init parse_dtb(void) > > #endif > > } > > > > +#if defined(CONFIG_RISCV_COMBO_SPINLOCKS) > > +DEFINE_STATIC_KEY_TRUE(qspinlock_key); > > +EXPORT_SYMBOL(qspinlock_key); > > +#endif > > + > > +static void __init riscv_spinlock_init(void) > > +{ > > + char *using_ext = NULL; > > + > > + if (IS_ENABLED(CONFIG_RISCV_TICKET_SPINLOCKS)) { > > + pr_info("Ticket spinlock: enabled\n"); > > + return; > > + } > > + > > + if (IS_ENABLED(CONFIG_RISCV_ISA_ZABHA) && > > + IS_ENABLED(CONFIG_RISCV_ISA_ZACAS) && > > + riscv_isa_extension_available(NULL, ZABHA) && > > + riscv_isa_extension_available(NULL, ZACAS)) { > > + using_ext = "using Zabha"; > > + } else if (riscv_isa_extension_available(NULL, ZICCRSE)) { > > + using_ext = "using Ziccrse"; > > + } > > +#if defined(CONFIG_RISCV_COMBO_SPINLOCKS) > > + else { > > else if (IS_ENABLED(CONFIG_RISCV_COMBO_SPINLOCKS)) It fails to compile because the static key is only declared when CONFIG_RISCV_COMBO_SPINLOCKS is set. > > > + static_branch_disable(&qspinlock_key); > > + pr_info("Ticket spinlock: enabled\n"); > > + > > nit: remove this blank line Done > > > + return; > > + } > > +#endif > > + > > + if (!using_ext) > > + pr_err("Queued spinlock without Zabha or Ziccrse"); > > + else > > + pr_info("Queued spinlock %s: enabled\n", using_ext); > > +} > > + > > extern void __init init_rt_signal_env(void); > > > > void __init setup_arch(char **cmdline_p) > > @@ -297,6 +334,7 @@ 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 > > I'm not sure what's better/worse, but instead of inventing this > __no_arch_spinlock_redefine thing we could just name all the functions > something like __arch_spin* and then add defines for both to asm/spinlock.h, > i.e. > > #define queued_spin_lock(l) __arch_spin_lock(l) > ... > > #define ticket_spin_lock(l) __arch_spin_lock(l) > ... __arch_spin_lock() would use queued_spin_lock() so that would make an "infinite recursive definition" right? And that would override the "real" queued_spin_lock() implementation too. But maybe I missed something! > > Besides not having to touch asm-generic/qspinlock.h and > asm-generic/ticket_spinlock.h it allows one to find the implementations > a bit easier as following a tag to arch_spin_lock() will take them to > queued_spin_lock() which will then take them to > arch/riscv/include/asm/spinlock.h and there they'll figure out how > __arch_spin_lock() was defined. > > > /* > > * 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 > > > > Thanks, > drew
