diff mbox series

[net-next,v2,06/10] gve: Avoid rescheduling napi if on wrong cpu

Message ID 20240501232549.1327174-7-shailend@google.com (mailing list archive)
State Accepted
Commit 9a5e0776d11f1ac9c740a6e24ff0e0facb6e3ddb
Delegated to: Netdev Maintainers
Headers show
Series gve: Implement queue api | expand

Checks

Context Check Description
netdev/series_format success Posting correctly formatted
netdev/tree_selection success Clearly marked for net-next, async
netdev/ynl success Generated files up to date; no warnings/errors; no diff in generated;
netdev/fixes_present success Fixes tag not required for -next series
netdev/header_inline success No static functions without inline keyword in header files
netdev/build_32bit success Errors and warnings before: 926 this patch: 926
netdev/build_tools success No tools touched, skip
netdev/cc_maintainers success CCed 11 of 11 maintainers
netdev/build_clang success Errors and warnings before: 940 this patch: 940
netdev/verify_signedoff success Signed-off-by tag matches author and committer
netdev/deprecated_api success None detected
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: 937 this patch: 937
netdev/checkpatch success total: 0 errors, 0 warnings, 0 checks, 76 lines checked
netdev/build_clang_rust success No Rust files in patch. Skipping build
netdev/kdoc success Errors and warnings before: 0 this patch: 0
netdev/source_inline success Was 0 now: 0
netdev/contest success net-next-2024-05-05--03-00 (tests: 1003)

Commit Message

Shailend Chand May 1, 2024, 11:25 p.m. UTC 
In order to make possible the implementation of per-queue ndo hooks,
gve_turnup was changed in a previous patch to account for queues already
having some unprocessed descriptors: it does a one-off napi_schdule to
handle them. If conditions of consistent high traffic persist in the
immediate aftermath of this, the poll routine for a queue can be "stuck"
on the cpu on which the ndo hooks ran, instead of the cpu its irq has
affinity with.

This situation is exacerbated by the fact that the ndo hooks for all the
queues are invoked on the same cpu, potentially causing all the napi
poll routines to be residing on the same cpu.

A self correcting mechanism in the poll method itself solves this
problem.

Tested-by: Mina Almasry <almasrymina@google.com>
Reviewed-by: Praveen Kaligineedi <pkaligineedi@google.com>
Reviewed-by: Harshitha Ramamurthy <hramamurthy@google.com>
Signed-off-by: Shailend Chand <shailend@google.com>
---
 drivers/net/ethernet/google/gve/gve.h      |  1 +
 drivers/net/ethernet/google/gve/gve_main.c | 33 ++++++++++++++++++++--
 2 files changed, 32 insertions(+), 2 deletions(-)
diff mbox series

Patch

diff --git a/drivers/net/ethernet/google/gve/gve.h b/drivers/net/ethernet/google/gve/gve.h
index 53b5244dc7bc..f27a6d5fbecf 100644
--- a/drivers/net/ethernet/google/gve/gve.h
+++ b/drivers/net/ethernet/google/gve/gve.h
@@ -610,6 +610,7 @@  struct gve_notify_block {
 	struct gve_priv *priv;
 	struct gve_tx_ring *tx; /* tx rings on this block */
 	struct gve_rx_ring *rx; /* rx rings on this block */
+	u32 irq;
 };
 
 /* Tracks allowed and current queue settings */
diff --git a/drivers/net/ethernet/google/gve/gve_main.c b/drivers/net/ethernet/google/gve/gve_main.c
index ef902b72b9a9..79b7a677ec0b 100644
--- a/drivers/net/ethernet/google/gve/gve_main.c
+++ b/drivers/net/ethernet/google/gve/gve_main.c
@@ -9,6 +9,7 @@ 
 #include <linux/etherdevice.h>
 #include <linux/filter.h>
 #include <linux/interrupt.h>
+#include <linux/irq.h>
 #include <linux/module.h>
 #include <linux/pci.h>
 #include <linux/sched.h>
@@ -253,6 +254,18 @@  static irqreturn_t gve_intr_dqo(int irq, void *arg)
 	return IRQ_HANDLED;
 }
 
+static int gve_is_napi_on_home_cpu(struct gve_priv *priv, u32 irq)
+{
+	int cpu_curr = smp_processor_id();
+	const struct cpumask *aff_mask;
+
+	aff_mask = irq_get_effective_affinity_mask(irq);
+	if (unlikely(!aff_mask))
+		return 1;
+
+	return cpumask_test_cpu(cpu_curr, aff_mask);
+}
+
 int gve_napi_poll(struct napi_struct *napi, int budget)
 {
 	struct gve_notify_block *block;
@@ -322,8 +335,21 @@  int gve_napi_poll_dqo(struct napi_struct *napi, int budget)
 		reschedule |= work_done == budget;
 	}
 
-	if (reschedule)
-		return budget;
+	if (reschedule) {
+		/* Reschedule by returning budget only if already on the correct
+		 * cpu.
+		 */
+		if (likely(gve_is_napi_on_home_cpu(priv, block->irq)))
+			return budget;
+
+		/* If not on the cpu with which this queue's irq has affinity
+		 * with, we avoid rescheduling napi and arm the irq instead so
+		 * that napi gets rescheduled back eventually onto the right
+		 * cpu.
+		 */
+		if (work_done == budget)
+			work_done--;
+	}
 
 	if (likely(napi_complete_done(napi, work_done))) {
 		/* Enable interrupts again.
@@ -428,6 +454,7 @@  static int gve_alloc_notify_blocks(struct gve_priv *priv)
 				"Failed to receive msix vector %d\n", i);
 			goto abort_with_some_ntfy_blocks;
 		}
+		block->irq = priv->msix_vectors[msix_idx].vector;
 		irq_set_affinity_hint(priv->msix_vectors[msix_idx].vector,
 				      get_cpu_mask(i % active_cpus));
 		block->irq_db_index = &priv->irq_db_indices[i].index;
@@ -441,6 +468,7 @@  static int gve_alloc_notify_blocks(struct gve_priv *priv)
 		irq_set_affinity_hint(priv->msix_vectors[msix_idx].vector,
 				      NULL);
 		free_irq(priv->msix_vectors[msix_idx].vector, block);
+		block->irq = 0;
 	}
 	kvfree(priv->ntfy_blocks);
 	priv->ntfy_blocks = NULL;
@@ -474,6 +502,7 @@  static void gve_free_notify_blocks(struct gve_priv *priv)
 		irq_set_affinity_hint(priv->msix_vectors[msix_idx].vector,
 				      NULL);
 		free_irq(priv->msix_vectors[msix_idx].vector, block);
+		block->irq = 0;
 	}
 	free_irq(priv->msix_vectors[priv->mgmt_msix_idx].vector, priv);
 	kvfree(priv->ntfy_blocks);