linux/drivers/hv/ring_buffer.c, branch v4.7

Drivers: hv: vmbus: Implement APIs to support "in place" consumption of vmbus packets

2016-04-30T21:00:19Z

Implement APIs for in-place consumption of vmbus packets. Currently, each packet is copied and processed one at a time and as part of processing each packet we potentially may signal the host (if it is waiting for room to produce a packet). These APIs help batched in-place processing of vmbus packets. We also optimize host signaling by having a separate API to signal the end of in-place consumption. With netvsc using these APIs, on an iperf run on average I see about 20X reduction in checks to signal the host. Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Move some ring buffer functions to hyperv.h

2016-04-30T21:00:19Z

In preparation for implementing APIs for in-place consumption of VMBUS packets, movve some ring buffer functionality into hyperv.h Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Use the new virt_xx barrier code

2016-04-30T21:00:19Z

Use the virt_xx barriers that have been defined for use in virtual machines. Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Use READ_ONCE() to read variables that are volatile

2016-04-30T21:00:19Z

Use the READ_ONCE macro to access variabes that can change asynchronously. This is the recommended mechanism for dealing with "unsafe" compiler optimizations. Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Introduce functions for estimating room in the ring buffer

2016-04-30T21:00:19Z

Introduce separate functions for estimating how much can be read from and written to the ring buffer. Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Fix signaling logic in hv_need_to_signal_on_read()

2016-04-30T21:00:16Z

On the consumer side, we have interrupt driven flow management of the producer. It is sufficient to base the signaling decision on the amount of space that is available to write after the read is complete. The current code samples the previous available space and uses this in making the signaling decision. This state can be stale and is unnecessary. Since the state can be stale, we end up not signaling the host (when we should) and this can result in a hang. Fix this problem by removing the unnecessary check. I would like to thank Arseney Romanenko for pointing out this issue. Also, issue a full memory barrier before making the signaling descision to correctly deal with potential reordering of the write (read index) followed by the read of pending_sz. Signed-off-by: K. Y. Srinivasan Tested-by: Dexuan Cui Cc: Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Give control over how the ring access is serialized

2016-02-08T05:34:12Z

On the channel send side, many of the VMBUS device drivers explicity serialize access to the outgoing ring buffer. Give more control to the VMBUS device drivers in terms how to serialize accesss to the outgoing ring buffer. The default behavior will be to aquire the ring lock to preserve the current behavior. Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman

Drivers: hv: vmbus: Eliminate the spin lock on the read path

2016-02-08T05:34:12Z

The function hv_ringbuffer_read() is called always on a pre-assigned CPU. Each chnnel is bound to a specific CPU and this function is always called on the CPU the channel is bound. There is no need to acquire the spin lock; get rid of this overhead. Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman

Drivers: hv: ring_buffer: eliminate hv_ringbuffer_peek()

2015-12-15T03:27:30Z

Currently, there is only one user for hv_ringbuffer_read()/ hv_ringbuffer_peak() functions and the usage of these functions is: - insecure as we drop ring_lock between them, someone else (in theory only) can acquire it in between; - non-optimal as we do a number of things (acquire/release the above mentioned lock, calculate available space on the ring, ...) twice and this path is performance-critical. Remove hv_ringbuffer_peek() moving the logic from __vmbus_recvpacket() to hv_ringbuffer_read(). Signed-off-by: Vitaly Kuznetsov Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman

Drivers: hv: ring_buffer: remove code duplication from hv_ringbuffer_peek/read()

2015-12-15T03:27:30Z

hv_ringbuffer_peek() does the same as hv_ringbuffer_read() without advancing the read index. The only functional change this patch brings is moving hv_need_to_signal_on_read() call under the ring_lock but this function is just a couple of comparisons. Signed-off-by: Vitaly Kuznetsov Signed-off-by: K. Y. Srinivasan Signed-off-by: Greg Kroah-Hartman