| Message ID | 20230715150032.6917-2-andy.chiu@sifive.com (mailing list archive) |
|---|---|
| State | Superseded |
| Headers | show |
| Series | riscv: support kernel-mode Vector | expand |
Hey Andy, Small bit of minor nitpickery.. On Sat, Jul 15, 2023 at 03:00:27PM +0000, Andy Chiu wrote: > User's will use its Vector registers only after the kernel really Looks like the ' here can be removed. > returns to the userspace. So we can delay restoring Vector registers as > long as we are still running in kernel mode. So, add a thread flag to > indicates the need of restoring Vector and do the restore at the last > arch-specific exit-to-user hook. This save the context restoring cost > when we switch over multiple processes that run V in kernel mode. For > example, if the kernel performs context swicth from A->B->C, and returns "a context switch" > to C's userspace, then there is no need for restoring B's V-register. "to restore" > > Besides, this also prevents us from repeatedly restoring V context when > executing kernel-mode Vector multiple times for the upcoming kenel-mode > Vector patches. > > Signed-off-by: Andy Chiu <andy.chiu@sifive.com> > --- > diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h > index 97e6f65ec176..d83975efe866 100644 > --- a/arch/riscv/include/asm/thread_info.h > +++ b/arch/riscv/include/asm/thread_info.h > @@ -101,12 +101,14 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src); > #define TIF_NOTIFY_SIGNAL 9 /* signal notifications exist */ > #define TIF_UPROBE 10 /* uprobe breakpoint or singlestep */ > #define TIF_32BIT 11 /* compat-mode 32bit process */ > +#define TIF_RISCV_V_DEFER_RESTORE 12 The rest of these have a comment, should the new addition? Anyway, no meaningful comments from me here Andy, Acked-by: Conor Dooley <conor.dooley@microchip.com> Thanks, Conor.
On Mon, Jul 17, 2023 at 5:47 PM Conor Dooley <conor.dooley@microchip.com> wrote: > > Hey Andy, > Small bit of minor nitpickery.. > > On Sat, Jul 15, 2023 at 03:00:27PM +0000, Andy Chiu wrote: > > User's will use its Vector registers only after the kernel really > > Looks like the ' here can be removed. > > > returns to the userspace. So we can delay restoring Vector registers as > > long as we are still running in kernel mode. So, add a thread flag to > > indicates the need of restoring Vector and do the restore at the last > > arch-specific exit-to-user hook. This save the context restoring cost > > when we switch over multiple processes that run V in kernel mode. For > > example, if the kernel performs context swicth from A->B->C, and returns > > "a context switch" > > > to C's userspace, then there is no need for restoring B's V-register. > > "to restore" Sorry for the poor english. Let me fix it in the next spin. > > > > > Besides, this also prevents us from repeatedly restoring V context when > > executing kernel-mode Vector multiple times for the upcoming kenel-mode > > Vector patches. > > > > Signed-off-by: Andy Chiu <andy.chiu@sifive.com> > > --- > > > diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h > > index 97e6f65ec176..d83975efe866 100644 > > --- a/arch/riscv/include/asm/thread_info.h > > +++ b/arch/riscv/include/asm/thread_info.h > > @@ -101,12 +101,14 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src); > > #define TIF_NOTIFY_SIGNAL 9 /* signal notifications exist */ > > #define TIF_UPROBE 10 /* uprobe breakpoint or singlestep */ > > #define TIF_32BIT 11 /* compat-mode 32bit process */ > > +#define TIF_RISCV_V_DEFER_RESTORE 12 > > The rest of these have a comment, should the new addition? Yes, it should. How about this "defer restoring process's V-context" > > Anyway, no meaningful comments from me here Andy, > Acked-by: Conor Dooley <conor.dooley@microchip.com> > > Thanks, > Conor.
diff --git a/arch/riscv/include/asm/entry-common.h b/arch/riscv/include/asm/entry-common.h index 6e4dee49d84b..52926f4d8d7c 100644 --- a/arch/riscv/include/asm/entry-common.h +++ b/arch/riscv/include/asm/entry-common.h @@ -4,6 +4,19 @@ #define _ASM_RISCV_ENTRY_COMMON_H #include <asm/stacktrace.h> +#include <asm/thread_info.h> +#include <asm/vector.h> + +static inline void arch_exit_to_user_mode_prepare(struct pt_regs *regs, + unsigned long ti_work) +{ + if (ti_work & _TIF_RISCV_V_DEFER_RESTORE) { + clear_thread_flag(TIF_RISCV_V_DEFER_RESTORE); + riscv_v_vstate_restore(current, regs); + } +} + +#define arch_exit_to_user_mode_prepare arch_exit_to_user_mode_prepare void handle_page_fault(struct pt_regs *regs); void handle_break(struct pt_regs *regs); diff --git a/arch/riscv/include/asm/thread_info.h b/arch/riscv/include/asm/thread_info.h index 97e6f65ec176..d83975efe866 100644 --- a/arch/riscv/include/asm/thread_info.h +++ b/arch/riscv/include/asm/thread_info.h @@ -101,12 +101,14 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src); #define TIF_NOTIFY_SIGNAL 9 /* signal notifications exist */ #define TIF_UPROBE 10 /* uprobe breakpoint or singlestep */ #define TIF_32BIT 11 /* compat-mode 32bit process */ +#define TIF_RISCV_V_DEFER_RESTORE 12 #define _TIF_NOTIFY_RESUME (1 << TIF_NOTIFY_RESUME) #define _TIF_SIGPENDING (1 << TIF_SIGPENDING) #define _TIF_NEED_RESCHED (1 << TIF_NEED_RESCHED) #define _TIF_NOTIFY_SIGNAL (1 << TIF_NOTIFY_SIGNAL) #define _TIF_UPROBE (1 << TIF_UPROBE) +#define _TIF_RISCV_V_DEFER_RESTORE (1 << TIF_RISCV_V_DEFER_RESTORE) #define _TIF_WORK_MASK \ (_TIF_NOTIFY_RESUME | _TIF_SIGPENDING | _TIF_NEED_RESCHED | \ diff --git a/arch/riscv/include/asm/vector.h b/arch/riscv/include/asm/vector.h index 3d78930cab51..a4f3705fd144 100644 --- a/arch/riscv/include/asm/vector.h +++ b/arch/riscv/include/asm/vector.h @@ -183,6 +183,15 @@ static inline void riscv_v_vstate_restore(struct task_struct *task, } } +static inline void riscv_v_vstate_set_restore(struct task_struct *task, + struct pt_regs *regs) +{ + if ((regs->status & SR_VS) != SR_VS_OFF) { + set_tsk_thread_flag(task, TIF_RISCV_V_DEFER_RESTORE); + riscv_v_vstate_on(regs); + } +} + static inline void __switch_to_vector(struct task_struct *prev, struct task_struct *next) { @@ -190,7 +199,7 @@ static inline void __switch_to_vector(struct task_struct *prev, regs = task_pt_regs(prev); riscv_v_vstate_save(prev, regs); - riscv_v_vstate_restore(next, task_pt_regs(next)); + riscv_v_vstate_set_restore(next, task_pt_regs(next)); } void riscv_v_vstate_ctrl_init(struct task_struct *tsk); diff --git a/arch/riscv/kernel/process.c b/arch/riscv/kernel/process.c index e32d737e039f..ec89e7edb6fd 100644 --- a/arch/riscv/kernel/process.c +++ b/arch/riscv/kernel/process.c @@ -153,6 +153,7 @@ void flush_thread(void) riscv_v_vstate_off(task_pt_regs(current)); kfree(current->thread.vstate.datap); memset(¤t->thread.vstate, 0, sizeof(struct __riscv_v_ext_state)); + clear_tsk_thread_flag(current, TIF_RISCV_V_DEFER_RESTORE); #endif } @@ -169,6 +170,7 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src) *dst = *src; /* clear entire V context, including datap for a new task */ memset(&dst->thread.vstate, 0, sizeof(struct __riscv_v_ext_state)); + clear_tsk_thread_flag(dst, TIF_RISCV_V_DEFER_RESTORE); return 0; } diff --git a/arch/riscv/kernel/signal.c b/arch/riscv/kernel/signal.c index 180d951d3624..0fca2c128b5f 100644 --- a/arch/riscv/kernel/signal.c +++ b/arch/riscv/kernel/signal.c @@ -134,7 +134,7 @@ static long __restore_v_state(struct pt_regs *regs, void __user *sc_vec) if (unlikely(err)) return err; - riscv_v_vstate_restore(current, regs); + riscv_v_vstate_set_restore(current, regs); return err; } diff --git a/arch/riscv/kernel/vector.c b/arch/riscv/kernel/vector.c index 8d92fb6c522c..9d583b760db4 100644 --- a/arch/riscv/kernel/vector.c +++ b/arch/riscv/kernel/vector.c @@ -167,7 +167,7 @@ bool riscv_v_first_use_handler(struct pt_regs *regs) return true; } riscv_v_vstate_on(regs); - riscv_v_vstate_restore(current, regs); + riscv_v_vstate_set_restore(current, regs); return true; }
User's will use its Vector registers only after the kernel really returns to the userspace. So we can delay restoring Vector registers as long as we are still running in kernel mode. So, add a thread flag to indicates the need of restoring Vector and do the restore at the last arch-specific exit-to-user hook. This save the context restoring cost when we switch over multiple processes that run V in kernel mode. For example, if the kernel performs context swicth from A->B->C, and returns to C's userspace, then there is no need for restoring B's V-register. Besides, this also prevents us from repeatedly restoring V context when executing kernel-mode Vector multiple times for the upcoming kenel-mode Vector patches. Signed-off-by: Andy Chiu <andy.chiu@sifive.com> --- arch/riscv/include/asm/entry-common.h | 13 +++++++++++++ arch/riscv/include/asm/thread_info.h | 2 ++ arch/riscv/include/asm/vector.h | 11 ++++++++++- arch/riscv/kernel/process.c | 2 ++ arch/riscv/kernel/signal.c | 2 +- arch/riscv/kernel/vector.c | 2 +- 6 files changed, 29 insertions(+), 3 deletions(-)