On 31/08/2017 20:06, Sukadev Bhattiprolu wrote:
felix [fe...@linux.vnet.ibm.com] wrote:
On 31/08/2017 01:32, Sukadev Bhattiprolu wrote:
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
Suka,
I am seconding Christophe on this matter. I think that your patch now
fulfills the CAPI use case requirements, with one exception: CAPI does not
restrict assigning a thread id to the current task. Please find a few minor
questions below.
Philippe
His patch is here:
https://urldefense.proofpoint.com/v2/url?u=https-3A__lists.ozlabs.org_pipermail_linuxppc-2Ddev_2017-2DAugust_161582.html&d=DwIFAw&c=jf_iaSHvJObTbx-siA1ZOg&r=KC0fX9VGJYXlSiH9qN2ZONDbh8vUCZFX8GUhF3rHAvg&m=XQenBfWewOBjWopgf1Fh2UAVGnlzq766MNuzx7jYfuA&s=07WOVTh9f_4IBZfCJes4lvc7LWenBlqVfAXIXxL2QH4&e=
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)
Why are you excluding ((1 << 15) - 1)?
You are right. I don't need to exclude that. Also, TIDR is a 16-bit (0:15 in
VAS's Local Notify TID) value right? So, will change to
#define MAX_THREAD_CONTEXT ((1 << 16) - 1)
Yes.
+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);
Why are you excluding 1?
I think the "_above" in the name is misleading. The function header for
ida_get_new_above() says "above or equal" so 1 is not excluded?
Understood.
+ 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);
CAPI does not have this restriction. It should be possible to assign a
thread id to an arbitrary task.
I see. We (or caller) just have to figure out the locking for the task.
The extension to any thread can be implemented in a separate patch.
'current' will do for now.
+ t->thread.tidr = assign_thread_tidr();
+ mtspr(SPRN_TIDR, t->thread.tidr);
+}
+
