diff options
| -rw-r--r-- | drivers/hv/channel.c | 7 | ||||
| -rw-r--r-- | include/linux/hyperv.h | 35 |
2 files changed, 41 insertions, 1 deletions
diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c index 9a49505a8e06..884cebf5f9b9 100644 --- a/drivers/hv/channel.c +++ b/drivers/hv/channel.c @@ -43,7 +43,12 @@ static void vmbus_setevent(struct vmbus_channel *channel) { struct hv_monitor_page *monitorpage; - if (channel->offermsg.monitor_allocated) { + /* + * For channels marked as in "low latency" mode + * bypass the monitor page mechanism. + */ + if ((channel->offermsg.monitor_allocated) && + (!channel->low_latency)) { /* Each u32 represents 32 channels */ sync_set_bit(channel->offermsg.child_relid & 31, (unsigned long *) vmbus_connection.send_int_page + diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h index 50f493eedeb5..755e8f566a47 100644 --- a/include/linux/hyperv.h +++ b/include/linux/hyperv.h @@ -850,6 +850,31 @@ struct vmbus_channel { * ring lock to preserve the current behavior. */ bool acquire_ring_lock; + /* + * For performance critical channels (storage, networking + * etc,), Hyper-V has a mechanism to enhance the throughput + * at the expense of latency: + * When the host is to be signaled, we just set a bit in a shared page + * and this bit will be inspected by the hypervisor within a certain + * window and if the bit is set, the host will be signaled. The window + * of time is the monitor latency - currently around 100 usecs. This + * mechanism improves throughput by: + * + * A) Making the host more efficient - each time it wakes up, + * potentially it will process morev number of packets. The + * monitor latency allows a batch to build up. + * B) By deferring the hypercall to signal, we will also minimize + * the interrupts. + * + * Clearly, these optimizations improve throughput at the expense of + * latency. Furthermore, since the channel is shared for both + * control and data messages, control messages currently suffer + * unnecessary latency adversley impacting performance and boot + * time. To fix this issue, permit tagging the channel as being + * in "low latency" mode. In this mode, we will bypass the monitor + * mechanism. + */ + bool low_latency; }; @@ -891,6 +916,16 @@ static inline void set_channel_pending_send_size(struct vmbus_channel *c, c->outbound.ring_buffer->pending_send_sz = size; } +static inline void set_low_latency_mode(struct vmbus_channel *c) +{ + c->low_latency = true; +} + +static inline void clear_low_latency_mode(struct vmbus_channel *c) +{ + c->low_latency = false; +} + void vmbus_onmessage(void *context); int vmbus_request_offers(void); |