[Xen-devel] [PATCH 06/11] evtchn: add FIFO-based event channel ABI

[David Vrabel <david.vrabel@xxxxxxxxxx>]

From: David Vrabel <david.vrabel@xxxxxxxxxx>

Add the event channel hypercall sub-ops and the definitions for the
shared data structures for the FIFO-based event channel ABI.

The design document for this new ABI is available here:

http://xenbits.xen.org/people/dvrabel/event-channels-F.pdf

In summary, events are reported using a per-domain shared event array
of event words.  Each event word has PENDING, LINKED and MASKED bits
and a LINK field for pointing to the next event in the event queue.

There are 16 event queues (with different priorities) per-VCPU.

Key advantages of this new ABI include:

- Support for over 100,000 events (2^17).
- 16 different event priorities.
- Improved fairness in event latency through the use of FIFOs.

Signed-off-by: David Vrabel <david.vrabel@xxxxxxxxxx>
Reviewed-by: Jan Beulich <jbeulich@xxxxxxxx>
---
 xen/include/public/event_channel.h |   75 ++++++++++++++++++++++++++++++++++++
 xen/include/public/xen.h           |    6 ++-
 xen/include/xen/sched.h            |    2 +-
 3 files changed, 80 insertions(+), 3 deletions(-)

diff --git a/xen/include/public/event_channel.h 
b/xen/include/public/event_channel.h
index 472efdb..4a53484 100644
--- a/xen/include/public/event_channel.h
+++ b/xen/include/public/event_channel.h
@@ -71,6 +71,9 @@
 #define EVTCHNOP_bind_vcpu        8
 #define EVTCHNOP_unmask           9
 #define EVTCHNOP_reset           10
+#define EVTCHNOP_init_control    11
+#define EVTCHNOP_expand_array    12
+#define EVTCHNOP_set_priority    13
 /* ` } */
 
 typedef uint32_t evtchn_port_t;
@@ -258,6 +261,43 @@ struct evtchn_reset {
 typedef struct evtchn_reset evtchn_reset_t;
 
 /*
+ * EVTCHNOP_init_control: initialize the control block for the FIFO ABI.
+ *
+ * Note: any events that are currently pending will not be resent and
+ * will be lost.  Guests should call this before binding any event to
+ * avoid losing any events.
+ */
+struct evtchn_init_control {
+    /* IN parameters. */
+    uint64_t control_gfn;
+    uint32_t offset;
+    uint32_t vcpu;
+    /* OUT parameters. */
+    uint8_t link_bits;
+    uint8_t _pad[7];
+};
+typedef struct evtchn_init_control evtchn_init_control_t;
+
+/*
+ * EVTCHNOP_expand_array: add an additional page to the event array.
+ */
+struct evtchn_expand_array {
+    /* IN parameters. */
+    uint64_t array_gfn;
+};
+typedef struct evtchn_expand_array evtchn_expand_array_t;
+
+/*
+ * EVTCHNOP_set_priority: set the priority for an event channel.
+ */
+struct evtchn_set_priority {
+    /* IN parameters. */
+    uint32_t port;
+    uint32_t priority;
+};
+typedef struct evtchn_set_priority evtchn_set_priority_t;
+
+/*
  * ` enum neg_errnoval
  * ` HYPERVISOR_event_channel_op_compat(struct evtchn_op *op)
  * `
@@ -281,6 +321,41 @@ struct evtchn_op {
 typedef struct evtchn_op evtchn_op_t;
 DEFINE_XEN_GUEST_HANDLE(evtchn_op_t);
 
+/*
+ * 2-level ABI
+ */
+
+#define EVTCHN_2L_NR_CHANNELS (sizeof(xen_ulong_t) * sizeof(xen_ulong_t) * 64)
+
+/*
+ * FIFO ABI
+ */
+
+/* Events may have priorities from 0 (highest) to 15 (lowest). */
+#define EVTCHN_FIFO_PRIORITY_MAX     0
+#define EVTCHN_FIFO_PRIORITY_DEFAULT 7
+#define EVTCHN_FIFO_PRIORITY_MIN     15
+
+#define EVTCHN_FIFO_MAX_QUEUES (EVTCHN_FIFO_PRIORITY_MIN + 1)
+
+typedef uint32_t event_word_t;
+
+#define EVTCHN_FIFO_PENDING 31
+#define EVTCHN_FIFO_MASKED  30
+#define EVTCHN_FIFO_LINKED  29
+
+#define EVTCHN_FIFO_LINK_BITS 17
+#define EVTCHN_FIFO_LINK_MASK ((1 << EVTCHN_FIFO_LINK_BITS) - 1)
+
+#define EVTCHN_FIFO_NR_CHANNELS (1 << EVTCHN_FIFO_LINK_BITS)
+
+struct evtchn_fifo_control_block {
+    uint32_t ready;
+    uint32_t _rsvd;
+    uint32_t head[EVTCHN_FIFO_MAX_QUEUES];
+};
+typedef struct evtchn_fifo_control_block evtchn_fifo_control_block_t;
+
 #endif /* __XEN_PUBLIC_EVENT_CHANNEL_H__ */
 
 /*
diff --git a/xen/include/public/xen.h b/xen/include/public/xen.h
index b50bd05..8c5697e 100644
--- a/xen/include/public/xen.h
+++ b/xen/include/public/xen.h
@@ -552,11 +552,13 @@ struct multicall_entry {
 typedef struct multicall_entry multicall_entry_t;
 DEFINE_XEN_GUEST_HANDLE(multicall_entry_t);
 
+#if __XEN_INTERFACE_VERSION__ < 0x00040400
 /*
- * Event channel endpoints per domain:
+ * Event channel endpoints per domain (when using the 2-level ABI):
  *  1024 if a long is 32 bits; 4096 if a long is 64 bits.
  */
-#define NR_EVENT_CHANNELS (sizeof(xen_ulong_t) * sizeof(xen_ulong_t) * 64)
+#define NR_EVENT_CHANNELS EVTCHN_2L_NR_CHANNELS
+#endif
 
 struct vcpu_time_info {
     /*
diff --git a/xen/include/xen/sched.h b/xen/include/xen/sched.h
index 59f6161..098857c 100644
--- a/xen/include/xen/sched.h
+++ b/xen/include/xen/sched.h
@@ -61,7 +61,7 @@ extern struct domain *dom0;
 #define next_power_of_2(x)      (__RDU32((x)-1) + 1)
 
 /* Maximum number of event channels for any ABI. */
-#define MAX_NR_EVTCHNS NR_EVENT_CHANNELS
+#define MAX_NR_EVTCHNS EVTCHN_2L_NR_CHANNELS
 
 #define EVTCHNS_PER_BUCKET (PAGE_SIZE / next_power_of_2(sizeof(struct evtchn)))
 #define EVTCHNS_PER_GROUP  (BUCKETS_PER_GROUP * EVTCHNS_PER_BUCKET)
-- 
1.7.2.5


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