| Message ID | 20231225125847.2778638-8-guoren@kernel.org (mailing list archive) |
|---|---|
| State | Changes Requested |
| Headers | show |
| Series | riscv: Add Native/Paravirt qspinlock support | expand |
On Mon, Dec 25, 2023 at 07:58:40AM -0500, guoren@kernel.org wrote: > From: Guo Ren <guoren@linux.alibaba.com> > > Add a static key controlling whether virt_spin_lock() should be > called or not. When running on bare metal set the new key to > false. > > The VM guests should fall back to a Test-and-Set spinlock, > because fair locks have horrible lock 'holder' preemption issues. > The virt_spin_lock_key would shortcut for the queued_spin_lock_- > slowpath() function that allow virt_spin_lock to hijack it. > > Signed-off-by: Guo Ren <guoren@linux.alibaba.com> > Signed-off-by: Guo Ren <guoren@kernel.org> > --- > .../admin-guide/kernel-parameters.txt | 4 +++ > arch/riscv/include/asm/spinlock.h | 22 ++++++++++++++++ > arch/riscv/kernel/setup.c | 26 +++++++++++++++++++ > 3 files changed, 52 insertions(+) > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > index 2ac9f1511774..b7794c96d91e 100644 > --- a/Documentation/admin-guide/kernel-parameters.txt > +++ b/Documentation/admin-guide/kernel-parameters.txt > @@ -3997,6 +3997,10 @@ > no_uaccess_flush > [PPC] Don't flush the L1-D cache after accessing user data. > > + no_virt_spin [RISC-V] Disable virt_spin_lock in VM guest to use > + native_queued_spinlock when the nopvspin option is enabled. > + This would help vcpu=pcpu scenarios. > + > novmcoredd [KNL,KDUMP] > Disable device dump. Device dump allows drivers to > append dump data to vmcore so you can collect driver > diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h > index d07643c07aae..7bbcf3d9fff0 100644 > --- a/arch/riscv/include/asm/spinlock.h > +++ b/arch/riscv/include/asm/spinlock.h > @@ -4,6 +4,28 @@ > #define __ASM_RISCV_SPINLOCK_H > > #ifdef CONFIG_QUEUED_SPINLOCKS > +/* > + * The KVM guests fall back to a Test-and-Set spinlock, because fair locks > + * have horrible lock 'holder' preemption issues. The virt_spin_lock_key > + * would shortcut for the queued_spin_lock_slowpath() function that allow > + * virt_spin_lock to hijack it. > + */ > +DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); > + > +#define virt_spin_lock virt_spin_lock > +static inline bool virt_spin_lock(struct qspinlock *lock) > +{ > + if (!static_branch_likely(&virt_spin_lock_key)) > + return false; > + > + do { > + while (atomic_read(&lock->val) != 0) > + cpu_relax(); > + } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0); > + > + return true; > +} > + > #define _Q_PENDING_LOOPS (1 << 9) > #endif > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > index d9072a59831c..0bafb9fd6ea3 100644 > --- a/arch/riscv/kernel/setup.c > +++ b/arch/riscv/kernel/setup.c > @@ -27,6 +27,7 @@ > #include <asm/cacheflush.h> > #include <asm/cpufeature.h> > #include <asm/cpu_ops.h> > +#include <asm/cpufeature.h> > #include <asm/early_ioremap.h> > #include <asm/pgtable.h> > #include <asm/setup.h> > @@ -266,6 +267,27 @@ early_param("qspinlock", queued_spinlock_setup); > DEFINE_STATIC_KEY_TRUE(combo_qspinlock_key); > EXPORT_SYMBOL(combo_qspinlock_key); > > +#ifdef CONFIG_QUEUED_SPINLOCKS > +static bool no_virt_spin __ro_after_init; > +static int __init no_virt_spin_setup(char *p) > +{ > + no_virt_spin = true; > + > + return 0; > +} > +early_param("no_virt_spin", no_virt_spin_setup); > + > +DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); > + > +static void __init virt_spin_lock_init(void) > +{ > + if (no_virt_spin) > + static_branch_disable(&virt_spin_lock_key); > + else > + pr_info("Enable virt_spin_lock\n"); > +} > +#endif > + > static void __init riscv_spinlock_init(void) > { > if (!enable_qspinlock) { > @@ -274,6 +296,10 @@ static void __init riscv_spinlock_init(void) > } else { > pr_info("Queued spinlock: enabled\n"); > } > + > +#ifdef CONFIG_QUEUED_SPINLOCKS > + virt_spin_lock_init(); > +#endif > } > #endif > > -- > 2.40.1 > LGTM: Reviewed-by: Leonardo Bras <leobras@redhat.com>
diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt index 2ac9f1511774..b7794c96d91e 100644 --- a/Documentation/admin-guide/kernel-parameters.txt +++ b/Documentation/admin-guide/kernel-parameters.txt @@ -3997,6 +3997,10 @@ no_uaccess_flush [PPC] Don't flush the L1-D cache after accessing user data. + no_virt_spin [RISC-V] Disable virt_spin_lock in VM guest to use + native_queued_spinlock when the nopvspin option is enabled. + This would help vcpu=pcpu scenarios. + novmcoredd [KNL,KDUMP] Disable device dump. Device dump allows drivers to append dump data to vmcore so you can collect driver diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h index d07643c07aae..7bbcf3d9fff0 100644 --- a/arch/riscv/include/asm/spinlock.h +++ b/arch/riscv/include/asm/spinlock.h @@ -4,6 +4,28 @@ #define __ASM_RISCV_SPINLOCK_H #ifdef CONFIG_QUEUED_SPINLOCKS +/* + * The KVM guests fall back to a Test-and-Set spinlock, because fair locks + * have horrible lock 'holder' preemption issues. The virt_spin_lock_key + * would shortcut for the queued_spin_lock_slowpath() function that allow + * virt_spin_lock to hijack it. + */ +DECLARE_STATIC_KEY_TRUE(virt_spin_lock_key); + +#define virt_spin_lock virt_spin_lock +static inline bool virt_spin_lock(struct qspinlock *lock) +{ + if (!static_branch_likely(&virt_spin_lock_key)) + return false; + + do { + while (atomic_read(&lock->val) != 0) + cpu_relax(); + } while (atomic_cmpxchg(&lock->val, 0, _Q_LOCKED_VAL) != 0); + + return true; +} + #define _Q_PENDING_LOOPS (1 << 9) #endif diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c index d9072a59831c..0bafb9fd6ea3 100644 --- a/arch/riscv/kernel/setup.c +++ b/arch/riscv/kernel/setup.c @@ -27,6 +27,7 @@ #include <asm/cacheflush.h> #include <asm/cpufeature.h> #include <asm/cpu_ops.h> +#include <asm/cpufeature.h> #include <asm/early_ioremap.h> #include <asm/pgtable.h> #include <asm/setup.h> @@ -266,6 +267,27 @@ early_param("qspinlock", queued_spinlock_setup); DEFINE_STATIC_KEY_TRUE(combo_qspinlock_key); EXPORT_SYMBOL(combo_qspinlock_key); +#ifdef CONFIG_QUEUED_SPINLOCKS +static bool no_virt_spin __ro_after_init; +static int __init no_virt_spin_setup(char *p) +{ + no_virt_spin = true; + + return 0; +} +early_param("no_virt_spin", no_virt_spin_setup); + +DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); + +static void __init virt_spin_lock_init(void) +{ + if (no_virt_spin) + static_branch_disable(&virt_spin_lock_key); + else + pr_info("Enable virt_spin_lock\n"); +} +#endif + static void __init riscv_spinlock_init(void) { if (!enable_qspinlock) { @@ -274,6 +296,10 @@ static void __init riscv_spinlock_init(void) } else { pr_info("Queued spinlock: enabled\n"); } + +#ifdef CONFIG_QUEUED_SPINLOCKS + virt_spin_lock_init(); +#endif } #endif