diff mbox series

[v2,net-next] ibmvnic: Toggle between queue types in affinity mapping

Message ID 20230127214358.318152-1-nnac123@linux.ibm.com (mailing list archive)
State Accepted
Commit 6831582937bd23fc1640e6f65620ebf75b3b9ef4
Delegated to: Netdev Maintainers
Headers show
Series [v2,net-next] ibmvnic: Toggle between queue types in affinity mapping | expand

Checks

Context Check Description
netdev/tree_selection success Clearly marked for net-next
netdev/fixes_present success Fixes tag not required for -next series
netdev/subject_prefix success Link
netdev/cover_letter success Single patches do not need cover letters
netdev/patch_count success Link
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 0 this patch: 0
netdev/cc_maintainers warning 11 maintainers not CCed: christophe.leroy@csgroup.eu linuxppc-dev@lists.ozlabs.org kuba@kernel.org davem@davemloft.net pabeni@redhat.com danymadden@us.ibm.com ricklind@linux.ibm.com edumazet@google.com mpe@ellerman.id.au npiggin@gmail.com tlfalcon@linux.ibm.com
netdev/build_clang success Errors and warnings before: 0 this patch: 0
netdev/module_param success Was 0 now: 0
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/check_selftest success No net selftest shell script
netdev/verify_fixes success No Fixes tag
netdev/build_allmodconfig_warn success Errors and warnings before: 0 this patch: 0
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 54 lines checked
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0

Commit Message

Nick Child Jan. 27, 2023, 9:43 p.m. UTC 
Previously, ibmvnic IRQs were assigned to CPU numbers by assigning all
the IRQs for transmit queues then assigning all the IRQs for receive
queues. With multi-threaded processors, in a heavy RX or TX environment,
physical cores would either be overloaded or underutilized (due to the
IRQ assignment algorithm). This approach is sub-optimal because IRQs for
the same subprocess (RX or TX) would be bound to adjacent CPU numbers,
meaning they were more likely to be contending for the same core.

For example, in a system with 64 CPU's and 32 queues, the IRQs would
be bound to CPU in the following pattern:

IRQ type |  CPU number
-----------------------
TX0	 |	0-1
TX1	 |	2-3
<etc>
RX0	 |	32-33
RX1	 |	34-35
<etc>

Observe that in SMT-8, the first 4 tx queues would be sharing the
same core.

A more optimal algorithm would balance the number RX and TX IRQ's across
the physical cores. Therefore, to increase performance, distribute RX and
TX IRQs across cores by alternating between assigning IRQs for RX and TX
queues to CPUs.
With a system with 64 CPUs and 32 queues, this results in the following
pattern:

IRQ type |  CPU number
-----------------------
TX0	 |	0-1
RX0	 |	2-3
TX1	 |	4-5
RX1	 |	6-7
<etc>

Observe that in SMT-8, there is equal distribution of RX and TX IRQs
per core. In the above case, each core handles 2 TX and 2 RX IRQ's.

Signed-off-by: Nick Child <nnac123@linux.ibm.com>
Reviewed-by: Haren Myneni <haren@linux.ibm.com>
---
Changes from v1[1]:
 - Assign from first queue instead of last queue
[1] https://lore.kernel.org/netdev/20230125101423.7b9590fe@kernel.org/T/#t

 drivers/net/ethernet/ibm/ibmvnic.c | 29 ++++++++++++++++-------------
 1 file changed, 16 insertions(+), 13 deletions(-)

Comments

patchwork-bot+netdevbpf@kernel.org Jan. 31, 2023, 9:30 a.m. UTC | #1 
Hello:

This patch was applied to netdev/net-next.git (master)
by Paolo Abeni <pabeni@redhat.com>:

On Fri, 27 Jan 2023 15:43:58 -0600 you wrote:
> Previously, ibmvnic IRQs were assigned to CPU numbers by assigning all
> the IRQs for transmit queues then assigning all the IRQs for receive
> queues. With multi-threaded processors, in a heavy RX or TX environment,
> physical cores would either be overloaded or underutilized (due to the
> IRQ assignment algorithm). This approach is sub-optimal because IRQs for
> the same subprocess (RX or TX) would be bound to adjacent CPU numbers,
> meaning they were more likely to be contending for the same core.
> 
> [...]

Here is the summary with links:
  - [v2,net-next] ibmvnic: Toggle between queue types in affinity mapping
    https://git.kernel.org/netdev/net-next/c/6831582937bd

You are awesome, thank you!
diff mbox series

Patch

diff --git a/drivers/net/ethernet/ibm/ibmvnic.c b/drivers/net/ethernet/ibm/ibmvnic.c
index e19a6bb3f444..146ca1d8031b 100644
--- a/drivers/net/ethernet/ibm/ibmvnic.c
+++ b/drivers/net/ethernet/ibm/ibmvnic.c
@@ -250,10 +250,11 @@  static void ibmvnic_set_affinity(struct ibmvnic_adapter *adapter)
 	struct ibmvnic_sub_crq_queue **rxqs = adapter->rx_scrq;
 	struct ibmvnic_sub_crq_queue **txqs = adapter->tx_scrq;
 	struct ibmvnic_sub_crq_queue *queue;
-	int num_rxqs = adapter->num_active_rx_scrqs;
-	int num_txqs = adapter->num_active_tx_scrqs;
+	int num_rxqs = adapter->num_active_rx_scrqs, i_rxqs = 0;
+	int num_txqs = adapter->num_active_tx_scrqs, i_txqs = 0;
 	int total_queues, stride, stragglers, i;
 	unsigned int num_cpu, cpu;
+	bool is_rx_queue;
 	int rc = 0;
 
 	netdev_dbg(adapter->netdev, "%s: Setting irq affinity hints", __func__);
@@ -273,14 +274,24 @@  static void ibmvnic_set_affinity(struct ibmvnic_adapter *adapter)
 	/* next available cpu to assign irq to */
 	cpu = cpumask_next(-1, cpu_online_mask);
 
-	for (i = 0; i < num_txqs; i++) {
-		queue = txqs[i];
+	for (i = 0; i < total_queues; i++) {
+		is_rx_queue = false;
+		/* balance core load by alternating rx and tx assignments
+		 * ex: TX0 -> RX0 -> TX1 -> RX1 etc.
+		 */
+		if ((i % 2 == 1 && i_rxqs < num_rxqs) || i_txqs == num_txqs) {
+			queue = rxqs[i_rxqs++];
+			is_rx_queue = true;
+		} else {
+			queue = txqs[i_txqs++];
+		}
+
 		rc = ibmvnic_set_queue_affinity(queue, &cpu, &stragglers,
 						stride);
 		if (rc)
 			goto out;
 
-		if (!queue)
+		if (!queue || is_rx_queue)
 			continue;
 
 		rc = __netif_set_xps_queue(adapter->netdev,
@@ -291,14 +302,6 @@  static void ibmvnic_set_affinity(struct ibmvnic_adapter *adapter)
 				    __func__, i, rc);
 	}
 
-	for (i = 0; i < num_rxqs; i++) {
-		queue = rxqs[i];
-		rc = ibmvnic_set_queue_affinity(queue, &cpu, &stragglers,
-						stride);
-		if (rc)
-			goto out;
-	}
-
 out:
 	if (rc) {
 		netdev_warn(adapter->netdev,