Commit b69ffeaa authored by Long Li's avatar Long Li Committed by Martin K. Petersen
Browse files

scsi: storvsc: Prefer returning channel with the same CPU as on the I/O issuing CPU 



When selecting an outgoing channel for I/O, storvsc tries to select a
channel with a returning CPU that is not the same as issuing CPU. This
worked well in the past, however it doesn't work well when the Hyper-V
exposes a large number of channels (up to the number of all CPUs). Use a
different CPU for returning channel is not efficient on Hyper-V.

Change this behavior by preferring to the channel with the same CPU as
the current I/O issuing CPU whenever possible.

Tests have shown improvements in newer Hyper-V/Azure environment, and no
regression with older Hyper-V/Azure environments.

Tested-by: default avatarRaheel Abdul Faizy <rabdulfaizy@microsoft.com>
Signed-off-by: default avatarLong Li <longli@microsoft.com>
Message-Id: <1759381530-7414-1-git-send-email-longli@linux.microsoft.com>
Signed-off-by: default avatarMartin K. Petersen <martin.petersen@oracle.com>
parent 558ae457

drivers/scsi/storvsc_drv.c

+45 −51
Original line number Diff line number Diff line
@@ -1406,14 +1406,19 @@ static struct vmbus_channel *get_og_chn(struct storvsc_device *stor_device, 
	}



	/*

	 * Our channel array is sparsley populated and we

	 * Our channel array could be sparsley populated and we

	 * initiated I/O on a processor/hw-q that does not

	 * currently have a designated channel. Fix this.

	 * The strategy is simple:

	 * I. Ensure NUMA locality

	 * II. Distribute evenly (best effort)

	 * I. Prefer the channel associated with the current CPU

	 * II. Ensure NUMA locality

	 * III. Distribute evenly (best effort)

	 */



	/* Prefer the channel on the I/O issuing processor/hw-q */

	if (cpumask_test_cpu(q_num, &stor_device->alloced_cpus))

		return stor_device->stor_chns[q_num];



	node_mask = cpumask_of_node(cpu_to_node(q_num));



	num_channels = 0;
@@ -1469,59 +1474,48 @@ static int storvsc_do_io(struct hv_device *device, 
	/* See storvsc_change_target_cpu(). */

	outgoing_channel = READ_ONCE(stor_device->stor_chns[q_num]);

	if (outgoing_channel != NULL) {

		if (outgoing_channel->target_cpu == q_num) {

		if (hv_get_avail_to_write_percent(&outgoing_channel->outbound)

				> ring_avail_percent_lowater)

			goto found_channel;



		/*

			 * Ideally, we want to pick a different channel if

			 * available on the same NUMA node.

		 * Channel is busy, try to find a channel on the same NUMA node

		 */

		node_mask = cpumask_of_node(cpu_to_node(q_num));

			for_each_cpu_wrap(tgt_cpu,

				 &stor_device->alloced_cpus, q_num + 1) {

		for_each_cpu_wrap(tgt_cpu, &stor_device->alloced_cpus,

				  q_num + 1) {

			if (!cpumask_test_cpu(tgt_cpu, node_mask))

				continue;

				if (tgt_cpu == q_num)

			channel = READ_ONCE(stor_device->stor_chns[tgt_cpu]);

			if (!channel)

				continue;

				channel = READ_ONCE(

					stor_device->stor_chns[tgt_cpu]);

				if (channel == NULL)

					continue;

				if (hv_get_avail_to_write_percent(

							&channel->outbound)

			if (hv_get_avail_to_write_percent(&channel->outbound)

					> ring_avail_percent_lowater) {

				outgoing_channel = channel;

				goto found_channel;

			}

		}



			/*

			 * All the other channels on the same NUMA node are

			 * busy. Try to use the channel on the current CPU

			 */

			if (hv_get_avail_to_write_percent(

						&outgoing_channel->outbound)

					> ring_avail_percent_lowater)

				goto found_channel;



		/*

		 * If we reach here, all the channels on the current

		 * NUMA node are busy. Try to find a channel in

			 * other NUMA nodes

		 * all NUMA nodes

		 */

			for_each_cpu(tgt_cpu, &stor_device->alloced_cpus) {

				if (cpumask_test_cpu(tgt_cpu, node_mask))

		for_each_cpu_wrap(tgt_cpu, &stor_device->alloced_cpus,

				  q_num + 1) {

			channel = READ_ONCE(stor_device->stor_chns[tgt_cpu]);

			if (!channel)

				continue;

				channel = READ_ONCE(

					stor_device->stor_chns[tgt_cpu]);

				if (channel == NULL)

					continue;

				if (hv_get_avail_to_write_percent(

							&channel->outbound)

			if (hv_get_avail_to_write_percent(&channel->outbound)

					> ring_avail_percent_lowater) {

				outgoing_channel = channel;

				goto found_channel;

			}

		}

		}

		/*

		 * If we reach here, all the channels are busy. Use the

		 * original channel found.

		 */

	} else {

		spin_lock_irqsave(&stor_device->lock, flags);

		outgoing_channel = stor_device->stor_chns[q_num];