On Thu, Aug 15, 2024 at 03:27:31PM GMT, Alexandre Ghiti wrote: > Hi Andrew, > > On 01/08/2024 08:53, Alexandre Ghiti wrote: > > 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? > > I'll let Andrea answer this as he asked for 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. > > That's NONPORTABLE, so people enabling this config are supposed to > > know that right? > > > > > > + > > > > +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 > > Done > > > > > > +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... > > > > > > > + > > > > +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? > > No, I'll check, thanks. > > > So I have just checked the size of the jump table section: > > * defconfig: > > - ticket: 26928 bytes > - combo: 28320 bytes > > So that's a ~5% increase. > > * ubuntu config > > - ticket: 107840 bytes > - combo: 174752 bytes > > And that's a ~62% increase. > > This is the ELF size difference between ticket and combo spinlocks: > > * ticket: 776915592 bytes > * combo: 786958968 bytes > > So that's an increase of ~1.3% on the ELF. > > And the .text section size: > > * ticket: 12290960 bytes > * combo: 12366644 bytes > > And that's a ~0.6% increase! > > Finally, I'd say the impact is very limited :) Thanks for checking! drew
