Michael Neuling [mi...@neuling.org] wrote: > Suka, > > Please CC Christophe who as an alternative way of doing this. We ned to get > agreement across all users of TIDR/AS_notify...
Mikey, Thanks. There is overlap between the two patches. I will send a patch on top of Christophe's for the interfaces to assign/clear the TIDR value and clear the thread->tidr during arch_dup_task_struct(). I will also drop the CONFIG_VAS check since its not only for VAS. Christophe, can you let me know of any other comments on this patch? Suka > > His patch is here: > https://lists.ozlabs.org/pipermail/linuxppc-dev/2017-August/161582.html > > Mikey > > On Tue, 2017-08-29 at 19:38 -0700, Sukadev Bhattiprolu wrote: > > We need the SPRN_TIDR to be set for use with fast thread-wakeup > > (core-to-core wakeup) in VAS. Each user thread that has a receive > > window setup and expects to be notified when a sender issues a paste > > needs to have a unique SPRN_TIDR value. > > > > The SPRN_TIDR value only needs to unique within the process but for > > now we use a globally unique thread id as described below. > > > > Signed-off-by: Sukadev Bhattiprolu <suka...@linux.vnet.ibm.com> > > --- > > 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 | 4 ++ > > arch/powerpc/include/asm/switch_to.h | 3 ++ > > arch/powerpc/kernel/process.c | 97 > > ++++++++++++++++++++++++++++++++++++ > > 3 files changed, 104 insertions(+) > > > > diff --git a/arch/powerpc/include/asm/processor.h > > b/arch/powerpc/include/asm/processor.h > > index fab7ff8..bf6ba63 100644 > > --- a/arch/powerpc/include/asm/processor.h > > +++ b/arch/powerpc/include/asm/processor.h > > @@ -232,6 +232,10 @@ struct debug_reg { > > struct thread_struct { > > unsigned long ksp; /* Kernel stack pointer */ > > > > +#ifdef CONFIG_PPC_VAS > > + unsigned long tidr; > > +#endif > > + > > #ifdef CONFIG_PPC64 > > unsigned long ksp_vsid; > > #endif > > diff --git a/arch/powerpc/include/asm/switch_to.h > > b/arch/powerpc/include/asm/switch_to.h > > index 17c8380..4962455 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 void 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 1f0fd36..13abb22 100644 > > --- a/arch/powerpc/kernel/process.c > > +++ b/arch/powerpc/kernel/process.c > > @@ -1132,6 +1132,10 @@ static inline void restore_sprs(struct thread_struct > > *old_thread, > > mtspr(SPRN_TAR, new_thread->tar); > > } > > #endif > > +#ifdef CONFIG_PPC_VAS > > + if (old_thread->tidr != new_thread->tidr) > > + mtspr(SPRN_TIDR, new_thread->tidr); > > +#endif > > } > > > > #ifdef CONFIG_PPC_BOOK3S_64 > > @@ -1446,9 +1450,97 @@ void flush_thread(void) > > #endif /* CONFIG_HAVE_HW_BREAKPOINT */ > > } > > > > +#ifdef CONFIG_PPC_VAS > > +static DEFINE_SPINLOCK(vas_thread_id_lock); > > +static DEFINE_IDA(vas_thread_ida); > > + > > +/* > > + * We need to assign an unique thread id to each thread in a process. This > > + * thread id is intended to be used with the Fast Thread-wakeup (aka Core- > > + * to-core wakeup) mechanism being implemented on top of Virtual > > Accelerator > > + * Switchboard (VAS). > > + * > > + * To get a unique thread-id per process we could simply use task_pid_nr() > > + * but the problem is that task_pid_nr() is not yet available for the > > thread > > + * when copy_thread() is called. Fixing that would require changing more > > + * intrusive arch-neutral code in code path in copy_process()?. > > + * > > + * Further, to assign unique thread ids 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 thraed ids 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 << 15) - 2) > > +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); > > +} > > + > > +void clear_thread_tidr(struct task_struct *t) > > +{ > > + if (t->thread.tidr) { > > + free_thread_tidr(t->thread.tidr); > > + t->thread.tidr = 0; > > + mtspr(SPRN_TIDR, 0); > > + } > > +} > > + > > +/* > > + * Assign an unique thread id for this thread and set it in the > > + * thread structure. For now, we need this interface only for > > + * the current task. > > + */ > > +void set_thread_tidr(struct task_struct *t) > > +{ > > + WARN_ON(t != current); > > + t->thread.tidr = assign_thread_tidr(); > > + mtspr(SPRN_TIDR, t->thread.tidr); > > +} > > + > > +#endif /* CONFIG_PPC_VAS */ > > + > > + > > void > > release_thread(struct task_struct *t) > > { > > +#ifdef CONFIG_PPC_VAS > > + clear_thread_tidr(t); > > +#endif > > } > > > > /* > > @@ -1474,6 +1566,8 @@ int arch_dup_task_struct(struct task_struct *dst, > > struct > > task_struct *src) > > > > clear_task_ebb(dst); > > > > + dst->thread.tidr = 0; > > + > > return 0; > > } > > > > @@ -1584,6 +1678,9 @@ int copy_thread(unsigned long clone_flags, unsigned > > long > > usp, > > #endif > > > > setup_ksp_vsid(p, sp); > > +#ifdef CONFIG_PPC_VAS > > + p->thread.tidr = 0; > > +#endif > > > > #ifdef CONFIG_PPC64 > > if (cpu_has_feature(CPU_FTR_DSCR)) {
