On Sun, Sep 17, 2023 at 11:12:31PM +0800, Guo Ren wrote: > On Thu, Sep 14, 2023 at 4:02 PM Leonardo Bras <leobras@xxxxxxxxxx> wrote: > > > > On Sun, Sep 10, 2023 at 04:29:02AM -0400, guoren@xxxxxxxxxx wrote: > > > From: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > > > > > 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 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. > > > > > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxxxxxxxxx> > > > Signed-off-by: Guo Ren <guoren@xxxxxxxxxx> > > > --- > > > .../admin-guide/kernel-parameters.txt | 4 +++ > > > arch/riscv/include/asm/sbi.h | 8 +++++ > > > arch/riscv/include/asm/spinlock.h | 22 ++++++++++++++ > > > arch/riscv/kernel/sbi.c | 2 +- > > > arch/riscv/kernel/setup.c | 30 ++++++++++++++++++- > > > 5 files changed, 64 insertions(+), 2 deletions(-) > > > > > > diff --git a/Documentation/admin-guide/kernel-parameters.txt b/Documentation/admin-guide/kernel-parameters.txt > > > index 61cacb8dfd0e..f75bedc50e00 100644 > > > --- a/Documentation/admin-guide/kernel-parameters.txt > > > +++ b/Documentation/admin-guide/kernel-parameters.txt > > > @@ -3927,6 +3927,10 @@ > > > 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 KVM 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/sbi.h b/arch/riscv/include/asm/sbi.h > > > index 501e06e52078..e0233b3d7a5f 100644 > > > --- a/arch/riscv/include/asm/sbi.h > > > +++ b/arch/riscv/include/asm/sbi.h > > > @@ -50,6 +50,13 @@ enum sbi_ext_base_fid { > > > SBI_EXT_BASE_GET_MIMPID, > > > }; > > > > > > +enum sbi_ext_base_impl_id { > > > + SBI_EXT_BASE_IMPL_ID_BBL = 0, > > > + SBI_EXT_BASE_IMPL_ID_OPENSBI, > > > + SBI_EXT_BASE_IMPL_ID_XVISOR, > > > + SBI_EXT_BASE_IMPL_ID_KVM, > > > +}; > > > + > > > enum sbi_ext_time_fid { > > > SBI_EXT_TIME_SET_TIMER = 0, > > > }; > > > @@ -269,6 +276,7 @@ int sbi_console_getchar(void); > > > long sbi_get_mvendorid(void); > > > long sbi_get_marchid(void); > > > long sbi_get_mimpid(void); > > > +long sbi_get_firmware_id(void); > > > void sbi_set_timer(uint64_t stime_value); > > > void sbi_shutdown(void); > > > void sbi_send_ipi(unsigned int cpu); > > > diff --git a/arch/riscv/include/asm/spinlock.h b/arch/riscv/include/asm/spinlock.h > > > index 8ea0fee80652..6b38d6616f14 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/sbi.c b/arch/riscv/kernel/sbi.c > > > index 88eea3a99ee0..cdd45edc8db4 100644 > > > --- a/arch/riscv/kernel/sbi.c > > > +++ b/arch/riscv/kernel/sbi.c > > > @@ -555,7 +555,7 @@ static inline long sbi_get_spec_version(void) > > > return __sbi_base_ecall(SBI_EXT_BASE_GET_SPEC_VERSION); > > > } > > > > > > -static inline long sbi_get_firmware_id(void) > > > +long sbi_get_firmware_id(void) > > > { > > > return __sbi_base_ecall(SBI_EXT_BASE_GET_IMP_ID); > > > } > > > diff --git a/arch/riscv/kernel/setup.c b/arch/riscv/kernel/setup.c > > > index 0f084f037651..c57d15b05160 100644 > > > --- a/arch/riscv/kernel/setup.c > > > +++ b/arch/riscv/kernel/setup.c > > > @@ -26,6 +26,7 @@ > > > #include <asm/alternative.h> > > > #include <asm/cacheflush.h> > > > #include <asm/cpu_ops.h> > > > +#include <asm/cpufeature.h> > > > #include <asm/early_ioremap.h> > > > #include <asm/pgtable.h> > > > #include <asm/setup.h> > > > @@ -283,16 +284,43 @@ DEFINE_STATIC_KEY_TRUE(combo_qspinlock_key); > > > EXPORT_SYMBOL(combo_qspinlock_key); > > > #endif > > > > > > +#ifdef CONFIG_QUEUED_SPINLOCKS > > > +static bool no_virt_spin_key = false; > > > > I suggest no _key, also there is no need for "= false". > > To be consistent with enable_qspinlock, I also suggest > > adding __ro_after_init: > > > > static bool no_virt_spin __ro_after_init; > okay. > > > > > > > > > > +DEFINE_STATIC_KEY_TRUE(virt_spin_lock_key); > > > + > > > +static int __init no_virt_spin_setup(char *p) > > > +{ > > > + no_virt_spin_key = true; > > > + > > > + return 0; > > > +} > > > +early_param("no_virt_spin", no_virt_spin_setup); > > > + > > > +static void __init virt_spin_lock_init(void) > > > +{ > > > + if (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM || > > > + no_virt_spin_key) > > > + static_branch_disable(&virt_spin_lock_key); > > > + else > > > + pr_info("Enable virt_spin_lock\n"); > > > +} > > > +#endif > > > + > > > > A new virt_no_spin kernel parameter was introduced, but without > > CONFIG_QUEUED_SPINLOCKS it will silently fail. > > > > I would suggest an #else clause here with a function to print an error / > > warning message about no_virt_spin being invalid in this scenario. > > It will probably help future debugging. > If CONFIG_QUEUED_SPINLOCKS=n, no_virt_spin should be quiet. The > no_virt_spin is one path of qspinlock. IIUC having no_virt_spin being passed as parameter to a kernel with CONFIG_QUEUED_SPINLOCKS=n is not supposed to have any warning this parameter is useless. I was just thinking it would be nice to have this warning during debugging, but if it's standard practice then I am ok with this. > > > > > > > > static void __init riscv_spinlock_init(void) > > > { > > > #ifdef CONFIG_RISCV_COMBO_SPINLOCKS > > > - if (!enable_qspinlock_key) { > > > + if (!enable_qspinlock_key && > > > + (sbi_get_firmware_id() != SBI_EXT_BASE_IMPL_ID_KVM)) { > > > static_branch_disable(&combo_qspinlock_key); > > > pr_info("Ticket spinlock: enabled\n"); > > > } else { > > > pr_info("Queued spinlock: enabled\n"); > > > } > > > #endif > > > + > > > +#ifdef CONFIG_QUEUED_SPINLOCKS > > > + virt_spin_lock_init(); > > > +#endif > > > } > > > > > > extern void __init init_rt_signal_env(void); > > > -- > > > 2.36.1 > > > > > > > I am probably missing something out, but it looks to me that this patch is > > causing 2 different changes: > > 1 - Enabling no_virt_spin parameter > > 2 - Disabling queued spinlocks for some firmware_id > > > > Wouldn't be better to split those changes in multiple patches? > > Or am I missing the point on why they need to be together? ^ Want your input on this Thanks! Leo > > > > Thanks! > > Leo > > > > > -- > Best Regards > Guo Ren >