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[09/22] wifi: iwlwifi: Use alloc_ordered_workqueue() to create ordered workqueues

Message ID 20230421025046.4008499-10-tj@kernel.org
State New
Headers show
Series None | expand

Commit Message

Tejun Heo April 21, 2023, 2:50 a.m. UTC
BACKGROUND
==========

When multiple work items are queued to a workqueue, their execution order
doesn't match the queueing order. They may get executed in any order and
simultaneously. When fully serialized execution - one by one in the queueing
order - is needed, an ordered workqueue should be used which can be created
with alloc_ordered_workqueue().

However, alloc_ordered_workqueue() was a later addition. Before it, an
ordered workqueue could be obtained by creating an UNBOUND workqueue with
@max_active==1. This originally was an implementation side-effect which was
broken by 4c16bd327c74 ("workqueue: restore WQ_UNBOUND/max_active==1 to be
ordered"). Because there were users that depended on the ordered execution,
5c0338c68706 ("workqueue: restore WQ_UNBOUND/max_active==1 to be ordered")
made workqueue allocation path to implicitly promote UNBOUND workqueues w/
@max_active==1 to ordered workqueues.

While this has worked okay, overloading the UNBOUND allocation interface
this way creates other issues. It's difficult to tell whether a given
workqueue actually needs to be ordered and users that legitimately want a
min concurrency level wq unexpectedly gets an ordered one instead. With
planned UNBOUND workqueue updates to improve execution locality and more
prevalence of chiplet designs which can benefit from such improvements, this
isn't a state we wanna be in forever.

This patch series audits all callsites that create an UNBOUND workqueue w/
@max_active==1 and converts them to alloc_ordered_workqueue() as necessary.

WHAT TO LOOK FOR
================

The conversions are from

  alloc_workqueue(WQ_UNBOUND | flags, 1, args..)

to

  alloc_ordered_workqueue(flags, args...)

which don't cause any functional changes. If you know that fully ordered
execution is not ncessary, please let me know. I'll drop the conversion and
instead add a comment noting the fact to reduce confusion while conversion
is in progress.

If you aren't fully sure, it's completely fine to let the conversion
through. The behavior will stay exactly the same and we can always
reconsider later.

As there are follow-up workqueue core changes, I'd really appreciate if the
patch can be routed through the workqueue tree w/ your acks. Thanks.

Signed-off-by: Tejun Heo <tj@kernel.org>
Cc: Kalle Valo <kvalo@kernel.org>
Cc: "David S. Miller" <davem@davemloft.net>
Cc: Eric Dumazet <edumazet@google.com>
Cc: Jakub Kicinski <kuba@kernel.org>
Cc: Paolo Abeni <pabeni@redhat.com>
Cc: Gregory Greenman <gregory.greenman@intel.com>
Cc: Johannes Berg <johannes.berg@intel.com>
Cc: Avraham Stern <avraham.stern@intel.com>
Cc: Kees Cook <keescook@chromium.org>
Cc: Mordechay Goodstein <mordechay.goodstein@intel.com>
Cc: "Haim, Dreyfuss" <haim.dreyfuss@intel.com>
Cc: linux-wireless@vger.kernel.org
Cc: netdev@vger.kernel.org
---
 drivers/net/wireless/intel/iwlwifi/pcie/trans.c | 4 ++--
 1 file changed, 2 insertions(+), 2 deletions(-)

Comments

Johannes Berg April 24, 2023, 5:31 p.m. UTC | #1
On Thu, 2023-04-20 at 16:50 -1000, Tejun Heo wrote:
> This patch series audits all callsites that create an UNBOUND workqueue w/
> @max_active==1 and converts them to alloc_ordered_workqueue() as necessary.
> 
> WHAT TO LOOK FOR
> ================
> 
> The conversions are from
> 
>   alloc_workqueue(WQ_UNBOUND | flags, 1, args..)
> 
> to
> 
>   alloc_ordered_workqueue(flags, args...)
> 
> which don't cause any functional changes. If you know that fully ordered
> execution is not ncessary, please let me know. I'll drop the conversion and
> instead add a comment noting the fact to reduce confusion while conversion
> is in progress.

This workqueue only has a single work struct queued on it, I'm not
_entirely_ sure why there's even a separate workqueue (possibly for
priority reasons etc.), but surely with just a single work struct, order
cannot really matter.

johannes
Tejun Heo May 8, 2023, 11:59 p.m. UTC | #2
Applied to wq/for-6.5-cleanup-ordered.

Thanks.
Tejun Heo May 9, 2023, 3:25 p.m. UTC | #3
On Mon, May 08, 2023 at 01:59:26PM -1000, Tejun Heo wrote:
> Applied to wq/for-6.5-cleanup-ordered.

This notification is on the wrong patch. The updated one w/ 0 @max_active
was applied.

Thanks.
diff mbox series

Patch

diff --git a/drivers/net/wireless/intel/iwlwifi/pcie/trans.c b/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
index 0a9af1ad1f20..cd17b601b172 100644
--- a/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
+++ b/drivers/net/wireless/intel/iwlwifi/pcie/trans.c
@@ -3576,8 +3576,8 @@  struct iwl_trans *iwl_trans_pcie_alloc(struct pci_dev *pdev,
 	init_waitqueue_head(&trans_pcie->fw_reset_waitq);
 	init_waitqueue_head(&trans_pcie->imr_waitq);
 
-	trans_pcie->rba.alloc_wq = alloc_workqueue("rb_allocator",
-						   WQ_HIGHPRI | WQ_UNBOUND, 1);
+	trans_pcie->rba.alloc_wq = alloc_ordered_workqueue("rb_allocator",
+							   WQ_HIGHPRI);
 	if (!trans_pcie->rba.alloc_wq) {
 		ret = -ENOMEM;
 		goto out_free_trans;