Re: [PATCH 1/3] drivers: hv: vmbus: Introduce latency testing

[Vitaly Kuznetsov]

Branden Bonaby <brandonbonaby94@xxxxxxxxx> writes:

> Introduce user specified latency in the packet reception path.
>
> Signed-off-by: Branden Bonaby <brandonbonaby94@xxxxxxxxx>
> ---
>  drivers/hv/connection.c  |  5 +++++
>  drivers/hv/ring_buffer.c | 10 ++++++++++
>  include/linux/hyperv.h   | 14 ++++++++++++++
>  3 files changed, 29 insertions(+)
>
> diff --git a/drivers/hv/connection.c b/drivers/hv/connection.c
> index 09829e15d4a0..2a2c22f5570e 100644
> --- a/drivers/hv/connection.c
> +++ b/drivers/hv/connection.c
> @@ -354,9 +354,14 @@ void vmbus_on_event(unsigned long data)
>  {
>  	struct vmbus_channel *channel = (void *) data;
>  	unsigned long time_limit = jiffies + 2;
> +	struct vmbus_channel *test_channel = !channel->primary_channel ?
> +						channel :
> +						channel->primary_channel;
>  
>  	trace_vmbus_on_event(channel);
>  
> +	if (unlikely(test_channel->fuzz_testing_buffer_delay > 0))
> +		udelay(test_channel->fuzz_testing_buffer_delay);
>  	do {
>  		void (*callback_fn)(void *);
>  
> diff --git a/drivers/hv/ring_buffer.c b/drivers/hv/ring_buffer.c
> index 9a03b163cbbd..d7627c9023d6 100644
> --- a/drivers/hv/ring_buffer.c
> +++ b/drivers/hv/ring_buffer.c
> @@ -395,7 +395,12 @@ struct vmpacket_descriptor *hv_pkt_iter_first(struct vmbus_channel *channel)
>  {
>  	struct hv_ring_buffer_info *rbi = &channel->inbound;
>  	struct vmpacket_descriptor *desc;
> +	struct vmbus_channel *test_channel = !channel->primary_channel ?
> +						channel :
> +						channel->primary_channel;
>  
> +	if (unlikely(test_channel->fuzz_testing_message_delay > 0))
> +		udelay(test_channel->fuzz_testing_message_delay);
>  	if (hv_pkt_iter_avail(rbi) < sizeof(struct vmpacket_descriptor))
>  		return NULL;
>  
> @@ -420,7 +425,12 @@ __hv_pkt_iter_next(struct vmbus_channel *channel,
>  	struct hv_ring_buffer_info *rbi = &channel->inbound;
>  	u32 packetlen = desc->len8 << 3;
>  	u32 dsize = rbi->ring_datasize;
> +	struct vmbus_channel *test_channel = !channel->primary_channel ?
> +						channel :
> +						channel->primary_channel;

This pattern is repeated 3 times so a define is justified. I would also
reversed the logic:

   test_channel = channel->primary_channel ? channel->primary_channel : channel;

>  
> +	if (unlikely(test_channel->fuzz_testing_message_delay > 0))
> +		udelay(test_channel->fuzz_testing_message_delay);

unlikely() is good but if it was under #ifdef it would've been even better.

>  	/* bump offset to next potential packet */
>  	rbi->priv_read_index += packetlen + VMBUS_PKT_TRAILER;
>  	if (rbi->priv_read_index >= dsize)
> diff --git a/include/linux/hyperv.h b/include/linux/hyperv.h
> index 6256cc34c4a6..8d068956dd67 100644
> --- a/include/linux/hyperv.h
> +++ b/include/linux/hyperv.h
> @@ -23,6 +23,7 @@
>  #include <linux/mod_devicetable.h>
>  #include <linux/interrupt.h>
>  #include <linux/reciprocal_div.h>
> +#include <linux/delay.h>
>  
>  #define MAX_PAGE_BUFFER_COUNT				32
>  #define MAX_MULTIPAGE_BUFFER_COUNT			32 /* 128K */
> @@ -926,6 +927,19 @@ struct vmbus_channel {
>  	 * full outbound ring buffer.
>  	 */
>  	u64 out_full_first;
> +
> +	/* enabling/disabling fuzz testing on the channel (default is false)*/
> +	bool fuzz_testing_state;
> +
> +	/* Buffer delay will delay the guest from emptying the ring buffer
> +	 * for a specific amount of time. The delay is in microseconds and will
> +	 * be between 1 to a maximum of 1000, its default is 0 (no delay).
> +	 * The  Message delay will delay guest reading on a per message basis
> +	 * in microseconds between 1 to 1000 with the default being 0
> +	 * (no delay).
> +	 */
> +	u32 fuzz_testing_buffer_delay;
> +	u32 fuzz_testing_message_delay;
>  };
>  
>  static inline bool is_hvsock_channel(const struct vmbus_channel *c)

-- 
Vitaly