linux-kernel - [PATCH v1 3/5] idpf: convert workqueues to unbound

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Message-ID: <20240813182747.1770032-4-manojvishy@google.com>
Date: Tue, 13 Aug 2024 18:27:45 +0000
From: Manoj Vishwanathan <manojvishy@...gle.com>
To: Tony Nguyen <anthony.l.nguyen@...el.com>, 
	Przemek Kitszel <przemyslaw.kitszel@...el.com>, "David S. Miller" <davem@...emloft.net>, 
	Eric Dumazet <edumazet@...gle.com>, intel-wired-lan@...ts.osuosl.org
Cc: netdev@...r.kernel.org, linux-kernel@...r.kernel.org, 
	google-lan-reviews@...glegroups.com, Marco Leogrande <leogrande@...gle.com>, 
	Manoj Vishwanathan <manojvishy@...gle.com>
Subject: [PATCH v1 3/5] idpf: convert workqueues to unbound

From: Marco Leogrande <leogrande@...gle.com>

When a workqueue is created with `WQ_UNBOUND`, its work items are
served by special worker-pools, whose host workers are not bound to
any specific CPU. In the default configuration (i.e. when
`queue_delayed_work` and friends do not specify which CPU to run the
work item on), `WQ_UNBOUND` allows the work item to be executed on any
CPU in the same node of the CPU it was enqueued on. While this
solution potentially sacrifices locality, it avoids contention with
other processes that might dominate the CPU time of the processor the
work item was scheduled on.

This is not just a theoretical problem: in b/317234476, a
misconfigured process was hogging most of the time from CPU0, leaving
less than 0.5% of its CPU time to the kworker. The IDPF workqueues
that were using the kworker on CPU0 suffered large completion delays
as a result, causing performance degradation, timeouts and eventual
system crash.

Tested:

* I have also run a manual test to gauge the performance
  improvement. The test consists of an antagonist process
  (`./stress --cpu 2`) consuming as much of CPU 0 as possible. This
  process is run under `taskset 01` to bind it to CPU0, and its
  priority is changed with `chrt -pQ 9900 10000 ${pid}` and
  `renice -n -20 ${pid}` after start.

  Then, the IDPF driver is forced to prefer CPU0 by editing all calls
  to `queue_delayed_work`, `mod_delayed_work`, etc... to use CPU 0.

  Finally, `ktraces` for the workqueue events are collected.

  Without the current patch, the antagonist process can force
  arbitrary delays between `workqueue_queue_work` and
  `workqueue_execute_start`, that in my tests were as high as
  `30ms`. With the current patch applied, the workqueue can be
  migrated to another unloaded CPU in the same node, and, keeping
  everything else equal, the maximum delay I could see was `6us`.

Signed-off-by: Marco Leogrande <leogrande@...gle.com>
Signed-off-by: Manoj Vishwanathan <manojvishy@...gle.com>
---
 drivers/net/ethernet/intel/idpf/idpf_main.c | 15 ++++++++++-----
 1 file changed, 10 insertions(+), 5 deletions(-)

diff --git a/drivers/net/ethernet/intel/idpf/idpf_main.c b/drivers/net/ethernet/intel/idpf/idpf_main.c
index db476b3314c8..dfd56fc5ff65 100644
--- a/drivers/net/ethernet/intel/idpf/idpf_main.c
+++ b/drivers/net/ethernet/intel/idpf/idpf_main.c
@@ -174,7 +174,8 @@ static int idpf_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 	pci_set_master(pdev);
 	pci_set_drvdata(pdev, adapter);

-	adapter->init_wq = alloc_workqueue("%s-%s-init", 0, 0,
+	adapter->init_wq = alloc_workqueue("%s-%s-init",
+					   WQ_UNBOUND | WQ_MEM_RECLAIM, 0,
 					   dev_driver_string(dev),
 					   dev_name(dev));
 	if (!adapter->init_wq) {
@@ -183,7 +184,8 @@ static int idpf_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto err_free;
 	}

-	adapter->serv_wq = alloc_workqueue("%s-%s-service", 0, 0,
+	adapter->serv_wq = alloc_workqueue("%s-%s-service",
+					   WQ_UNBOUND | WQ_MEM_RECLAIM, 0,
 					   dev_driver_string(dev),
 					   dev_name(dev));
 	if (!adapter->serv_wq) {
@@ -192,7 +194,8 @@ static int idpf_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto err_serv_wq_alloc;
 	}

-	adapter->mbx_wq = alloc_workqueue("%s-%s-mbx", 0, 0,
+	adapter->mbx_wq = alloc_workqueue("%s-%s-mbx",
+					  WQ_UNBOUND | WQ_MEM_RECLAIM, 0,
 					  dev_driver_string(dev),
 					  dev_name(dev));
 	if (!adapter->mbx_wq) {
@@ -201,7 +204,8 @@ static int idpf_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto err_mbx_wq_alloc;
 	}

-	adapter->stats_wq = alloc_workqueue("%s-%s-stats", 0, 0,
+	adapter->stats_wq = alloc_workqueue("%s-%s-stats",
+					    WQ_UNBOUND | WQ_MEM_RECLAIM, 0,
 					    dev_driver_string(dev),
 					    dev_name(dev));
 	if (!adapter->stats_wq) {
@@ -210,7 +214,8 @@ static int idpf_probe(struct pci_dev *pdev, const struct pci_device_id *ent)
 		goto err_stats_wq_alloc;
 	}

-	adapter->vc_event_wq = alloc_workqueue("%s-%s-vc_event", 0, 0,
+	adapter->vc_event_wq = alloc_workqueue("%s-%s-vc_event",
+					       WQ_UNBOUND | WQ_MEM_RECLAIM, 0,
 					       dev_driver_string(dev),
 					       dev_name(dev));
 	if (!adapter->vc_event_wq) {
-- 
2.46.0.76.ge559c4bf1a-goog