[PATCH v2 13/18] powerpc: Add support for setting SPRN_TIDR
Frederic Barrat
fbarrat at linux.vnet.ibm.com
Fri Oct 20 22:03:28 AEDT 2017
Le 07/10/2017 à 04:28, Sukadev Bhattiprolu a écrit :
> We need the SPRN_TIDR to be set for use with fast thread-wakeup (core-
> to-core wakeup) and also with CAPI.
>
> Each thread in a process needs to have a unique id within the process.
> But as explained below, for now, we assign globally unique thread ids
> to all threads in the system.
>
> Signed-off-by: Sukadev Bhattiprolu <sukadev at linux.vnet.ibm.com>
> Signed-off-by: Philippe Bergheaud <felix at linux.vnet.ibm.com>
> Signed-off-by: Christophe Lombard <clombard at linux.vnet.ibm.com>
> ---
FWIW
Reviewed-by: Frederic Barrat <fbarrat at linux.vnet.ibm.com>
> Changelog[v3]
> - Merge changes with and address comments to Christophe's patch.
> (i.e drop CONFIG_PPC_VAS; use CONFIG_PPC64; check CPU_ARCH_300
> before setting TIDR). Defer following to separate patches:
> - emulation parts of Christophe's patch,
> - setting TIDR for tasks other than 'current'
> - setting feature bit in AT_HWCAP2
>
> Changelog[v2]
> - Michael Ellerman: Use an interface to assign TIDR so it is
> assigned to only threads that need it; move assignment to
> restore_sprs(). Drop lint from rebase;
> ---
> arch/powerpc/include/asm/processor.h | 1 +
> arch/powerpc/include/asm/switch_to.h | 3 +
> arch/powerpc/kernel/process.c | 122 +++++++++++++++++++++++++++++++++++
> 3 files changed, 126 insertions(+)
>
> diff --git a/arch/powerpc/include/asm/processor.h b/arch/powerpc/include/asm/processor.h
> index fab7ff8..58cc212 100644
> --- a/arch/powerpc/include/asm/processor.h
> +++ b/arch/powerpc/include/asm/processor.h
> @@ -329,6 +329,7 @@ struct thread_struct {
> */
> int dscr_inherit;
> unsigned long ppr; /* used to save/restore SMT priority */
> + unsigned long tidr;
> #endif
> #ifdef CONFIG_PPC_BOOK3S_64
> unsigned long tar;
> diff --git a/arch/powerpc/include/asm/switch_to.h b/arch/powerpc/include/asm/switch_to.h
> index 17c8380..f5da32f 100644
> --- a/arch/powerpc/include/asm/switch_to.h
> +++ b/arch/powerpc/include/asm/switch_to.h
> @@ -91,4 +91,7 @@ static inline void clear_task_ebb(struct task_struct *t)
> #endif
> }
>
> +extern int set_thread_tidr(struct task_struct *t);
> +extern void clear_thread_tidr(struct task_struct *t);
> +
> #endif /* _ASM_POWERPC_SWITCH_TO_H */
> diff --git a/arch/powerpc/kernel/process.c b/arch/powerpc/kernel/process.c
> index 37ed60b..d861fcd 100644
> --- a/arch/powerpc/kernel/process.c
> +++ b/arch/powerpc/kernel/process.c
> @@ -1120,6 +1120,13 @@ static inline void restore_sprs(struct thread_struct *old_thread,
> mtspr(SPRN_TAR, new_thread->tar);
> }
> #endif
> +#ifdef CONFIG_PPC64
> + if (old_thread->tidr != new_thread->tidr) {
> + /* TIDR should be non-zero only with ISA3.0. */
> + WARN_ON_ONCE(!cpu_has_feature(CPU_FTR_ARCH_300));
> + mtspr(SPRN_TIDR, new_thread->tidr);
> + }
> +#endif
> }
>
> #ifdef CONFIG_PPC_BOOK3S_64
> @@ -1438,9 +1445,117 @@ void flush_thread(void)
> #endif /* CONFIG_HAVE_HW_BREAKPOINT */
> }
>
> +#ifdef CONFIG_PPC64
> +static DEFINE_SPINLOCK(vas_thread_id_lock);
> +static DEFINE_IDA(vas_thread_ida);
> +
> +/*
> + * We need to assign a unique thread id to each thread in a process.
> + *
> + * This thread id, referred to as TIDR, and separate from the Linux's tgid,
> + * is intended to be used to direct an ASB_Notify from the hardware to the
> + * thread, when a suitable event occurs in the system.
> + *
> + * One such event is a "paste" instruction in the context of Fast Thread
> + * Wakeup (aka Core-to-core wake up in the Virtual Accelerator Switchboard
> + * (VAS) in POWER9.
> + *
> + * To get a unique TIDR per process we could simply reuse task_pid_nr() but
> + * the problem is that task_pid_nr() is not yet available copy_thread() is
> + * called. Fixing that would require changing more intrusive arch-neutral
> + * code in code path in copy_process()?.
> + *
> + * Further, to assign unique TIDRs within each process, we need an atomic
> + * field (or an IDR) in task_struct, which again intrudes into the arch-
> + * neutral code. So try to assign globally unique TIDRs for now.
> + *
> + * NOTE: TIDR 0 indicates that the thread does not need a TIDR value.
> + * For now, only threads that expect to be notified by the VAS
> + * hardware need a TIDR value and we assign values > 0 for those.
> + */
> +#define MAX_THREAD_CONTEXT ((1 << 16) - 1)
> +static int assign_thread_tidr(void)
> +{
> + int index;
> + int err;
> +
> +again:
> + if (!ida_pre_get(&vas_thread_ida, GFP_KERNEL))
> + return -ENOMEM;
> +
> + spin_lock(&vas_thread_id_lock);
> + err = ida_get_new_above(&vas_thread_ida, 1, &index);
> + spin_unlock(&vas_thread_id_lock);
> +
> + if (err == -EAGAIN)
> + goto again;
> + else if (err)
> + return err;
> +
> + if (index > MAX_THREAD_CONTEXT) {
> + spin_lock(&vas_thread_id_lock);
> + ida_remove(&vas_thread_ida, index);
> + spin_unlock(&vas_thread_id_lock);
> + return -ENOMEM;
> + }
> +
> + return index;
> +}
> +
> +static void free_thread_tidr(int id)
> +{
> + spin_lock(&vas_thread_id_lock);
> + ida_remove(&vas_thread_ida, id);
> + spin_unlock(&vas_thread_id_lock);
> +}
> +
> +/*
> + * Clear any TIDR value assigned to this thread.
> + */
> +void clear_thread_tidr(struct task_struct *t)
> +{
> + if (!t->thread.tidr)
> + return;
> +
> + if (!cpu_has_feature(CPU_FTR_ARCH_300)) {
> + WARN_ON_ONCE(1);
> + return;
> + }
> +
> + mtspr(SPRN_TIDR, 0);
> + free_thread_tidr(t->thread.tidr);
> + t->thread.tidr = 0;
> +}
> +
> +/*
> + * Assign a unique TIDR (thread id) for task @t and set it in the thread
> + * structure. For now, we only support setting TIDR for 'current' task.
> + */
> +int set_thread_tidr(struct task_struct *t)
> +{
> + if (!cpu_has_feature(CPU_FTR_ARCH_300))
> + return -EINVAL;
> +
> + if (t != current)
> + return -EINVAL;
> +
> + t->thread.tidr = assign_thread_tidr();
> + if (t->thread.tidr < 0)
> + return t->thread.tidr;
> +
> + mtspr(SPRN_TIDR, t->thread.tidr);
> +
> + return 0;
> +}
> +
> +#endif /* CONFIG_PPC64 */
> +
> void
> release_thread(struct task_struct *t)
> {
> +#ifdef CONFIG_PPC64
> + clear_thread_tidr(t);
> +#endif
> }
>
> /*
> @@ -1466,6 +1581,10 @@ int arch_dup_task_struct(struct task_struct *dst, struct task_struct *src)
>
> clear_task_ebb(dst);
>
> +#ifdef CONFIG_PPC64
> + dst->thread.tidr = 0;
> +#endif
> +
> return 0;
> }
>
> @@ -1576,6 +1695,9 @@ int copy_thread(unsigned long clone_flags, unsigned long usp,
> #endif
>
> setup_ksp_vsid(p, sp);
> +#ifdef CONFIG_PPC64
> + p->thread.tidr = 0;
> +#endif
>
> #ifdef CONFIG_PPC64
> if (cpu_has_feature(CPU_FTR_DSCR)) {
>
More information about the Linuxppc-dev
mailing list