> -----Original Message-----
> From: Stephen Hemminger [mailto:step...@networkplumber.org]
> Sent: Tuesday, February 14, 2017 10:21 PM
> To: KY Srinivasan <k...@microsoft.com>; Haiyan Yang
> <haiy...@microsoft.com>
> Cc: de...@linuxdriverproject.org; Stephen Hemminger
> <sthem...@microsoft.com>
> Subject: [PATCH 6/8] vmbus: remove unused low_latency option
>
> This was intended for future use, but since the code is currently unused (and
> therefore dead and unused), remove it.
>
> It can be restored when there is a use case.
Stephen, I do have a use case for this. I wanted to get this into the Greg's
tree and then
Modify both netvsc and storvsc to use it. This is currently shipping as part of
Clear Linux
and makes a significant difference in the boot time on Hyper-V.
K. Y
>
> Signed-off-by: Stephen Hemminger <sthem...@microsoft.com>
> ---
> drivers/hv/channel.c | 2 +-
> include/linux/hyperv.h | 36 ------------------------------------
> 2 files changed, 1 insertion(+), 37 deletions(-)
>
> diff --git a/drivers/hv/channel.c b/drivers/hv/channel.c index
> deb852238b2d..01d5bdb69770 100644
> --- a/drivers/hv/channel.c
> +++ b/drivers/hv/channel.c
> @@ -47,7 +47,7 @@ void vmbus_setevent(struct vmbus_channel *channel)
> * For channels marked as in "low latency" mode
> * bypass the monitor page mechanism.
> */
> - if (channel->offermsg.monitor_allocated && !channel->low_latency) {
> + if (channel->offermsg.monitor_allocated) {
> vmbus_send_interrupt(channel->offermsg.child_relid);
>
> /* Get the child to parent monitor page */ diff --git
> a/include/linux/hyperv.h b/include/linux/hyperv.h index
> b8807da6ef72..09d10a4a34f4 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -853,32 +853,6 @@ struct vmbus_channel {
> struct rcu_head rcu;
>
> /*
> - * 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;
> -
> - /*
> * NUMA distribution policy:
> * We support teo policies:
> * 1) Balanced: Here all performance critical channels are @@ -926,16
> +900,6 @@ 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);
> --
> 2.11.0
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