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Message-ID: <aRS9Vk6yh1wEq614@gcabiddu-mobl.ger.corp.intel.com>
Date: Wed, 12 Nov 2025 17:01:10 +0000
From: Giovanni Cabiddu <giovanni.cabiddu@...el.com>
To: Marco Crivellari <marco.crivellari@...e.com>
CC: <linux-kernel@...r.kernel.org>, <linux-crypto@...r.kernel.org>,
<qat-linux@...el.com>, Tejun Heo <tj@...nel.org>, Lai Jiangshan
<jiangshanlai@...il.com>, Frederic Weisbecker <frederic@...nel.org>,
Sebastian Andrzej Siewior <bigeasy@...utronix.de>, Michal Hocko
<mhocko@...e.com>, Herbert Xu <herbert@...dor.apana.org.au>, "David S .
Miller" <davem@...emloft.net>
Subject: Re: [PATCH] crypto: qat - add WQ_PERCPU to alloc_workqueue users
Hi Marco,
On Fri, Nov 07, 2025 at 12:23:54PM +0100, Marco Crivellari wrote:
> Currently if a user enqueues a work item using schedule_delayed_work() the
> used wq is "system_wq" (per-cpu wq) while queue_delayed_work() use
> WORK_CPU_UNBOUND (used when a cpu is not specified). The same applies to
> schedule_work() that is using system_wq and queue_work(), that makes use
> again of WORK_CPU_UNBOUND.
> This lack of consistency cannot be addressed without refactoring the API.
The reference to WORK_CPU_UNBOUND in this paragraph got me a bit
confused :-). As I understand it, if a workqueue is allocated with default
parameters (i.e., no flags), it is per-CPU, so using queue_work() or
queue_delayed_work() on such a queue would behave similarly to
schedule_work() or schedule_delayed_work() in terms of CPU affinity.
Is the `lack of consistency` you are referring in this paragraph about
developer expectations? IOW developers might assume they're getting
unbound behavior?
> alloc_workqueue() treats all queues as per-CPU by default, while unbound
> workqueues must opt-in via WQ_UNBOUND.
>
> This default is suboptimal: most workloads benefit from unbound queues,
> allowing the scheduler to place worker threads where they’re needed and
> reducing noise when CPUs are isolated.
>
> This continues the effort to refactor workqueue APIs, which began with
> the introduction of new workqueues and a new alloc_workqueue flag in:
>
> commit 128ea9f6ccfb ("workqueue: Add system_percpu_wq and system_dfl_wq")
> commit 930c2ea566af ("workqueue: Add new WQ_PERCPU flag")
>
> This change adds a new WQ_PERCPU flag to explicitly request alloc_workqueue()
> to be per-cpu when WQ_UNBOUND has not been specified.
>
> With the introduction of the WQ_PERCPU flag (equivalent to !WQ_UNBOUND),
> any alloc_workqueue() caller that doesn’t explicitly specify WQ_UNBOUND
> must now use WQ_PERCPU.
>
> Once migration is complete, WQ_UNBOUND can be removed and unbound will
> become the implicit default.
>
> Suggested-by: Tejun Heo <tj@...nel.org>
> Signed-off-by: Marco Crivellari <marco.crivellari@...e.com>
Acked-by: Giovanni Cabiddu <giovanni.cabiddu@...el.com>
> ---
> drivers/crypto/intel/qat/qat_common/adf_aer.c | 4 ++--
> drivers/crypto/intel/qat/qat_common/adf_isr.c | 3 ++-
> drivers/crypto/intel/qat/qat_common/adf_sriov.c | 3 ++-
> drivers/crypto/intel/qat/qat_common/adf_vf_isr.c | 3 ++-
> 4 files changed, 8 insertions(+), 5 deletions(-)
>
> diff --git a/drivers/crypto/intel/qat/qat_common/adf_aer.c b/drivers/crypto/intel/qat/qat_common/adf_aer.c
> index 35679b21ff63..667d5e320f50 100644
> --- a/drivers/crypto/intel/qat/qat_common/adf_aer.c
> +++ b/drivers/crypto/intel/qat/qat_common/adf_aer.c
> @@ -276,11 +276,11 @@ int adf_notify_fatal_error(struct adf_accel_dev *accel_dev)
> int adf_init_aer(void)
> {
> device_reset_wq = alloc_workqueue("qat_device_reset_wq",
> - WQ_MEM_RECLAIM, 0);
> + WQ_MEM_RECLAIM | WQ_PERCPU, 0);
> if (!device_reset_wq)
> return -EFAULT;
>
> - device_sriov_wq = alloc_workqueue("qat_device_sriov_wq", 0, 0);
> + device_sriov_wq = alloc_workqueue("qat_device_sriov_wq", WQ_PERCPU, 0);
> if (!device_sriov_wq) {
> destroy_workqueue(device_reset_wq);
> device_reset_wq = NULL;
> diff --git a/drivers/crypto/intel/qat/qat_common/adf_isr.c b/drivers/crypto/intel/qat/qat_common/adf_isr.c
> index 12e565613661..4639d7fd93e6 100644
> --- a/drivers/crypto/intel/qat/qat_common/adf_isr.c
> +++ b/drivers/crypto/intel/qat/qat_common/adf_isr.c
> @@ -384,7 +384,8 @@ EXPORT_SYMBOL_GPL(adf_isr_resource_alloc);
> */
> int __init adf_init_misc_wq(void)
> {
> - adf_misc_wq = alloc_workqueue("qat_misc_wq", WQ_MEM_RECLAIM, 0);
> + adf_misc_wq = alloc_workqueue("qat_misc_wq",
> + WQ_MEM_RECLAIM | WQ_PERCPU, 0);
>
> return !adf_misc_wq ? -ENOMEM : 0;
> }
> diff --git a/drivers/crypto/intel/qat/qat_common/adf_sriov.c b/drivers/crypto/intel/qat/qat_common/adf_sriov.c
> index 31d1ef0cb1f5..bb904ba4bf84 100644
> --- a/drivers/crypto/intel/qat/qat_common/adf_sriov.c
> +++ b/drivers/crypto/intel/qat/qat_common/adf_sriov.c
> @@ -299,7 +299,8 @@ EXPORT_SYMBOL_GPL(adf_sriov_configure);
> int __init adf_init_pf_wq(void)
> {
> /* Workqueue for PF2VF responses */
> - pf2vf_resp_wq = alloc_workqueue("qat_pf2vf_resp_wq", WQ_MEM_RECLAIM, 0);
> + pf2vf_resp_wq = alloc_workqueue("qat_pf2vf_resp_wq",
> + WQ_MEM_RECLAIM | WQ_PERCPU, 0);
>
> return !pf2vf_resp_wq ? -ENOMEM : 0;
> }
> diff --git a/drivers/crypto/intel/qat/qat_common/adf_vf_isr.c b/drivers/crypto/intel/qat/qat_common/adf_vf_isr.c
> index a4636ec9f9ca..d0fef20a3df4 100644
> --- a/drivers/crypto/intel/qat/qat_common/adf_vf_isr.c
> +++ b/drivers/crypto/intel/qat/qat_common/adf_vf_isr.c
> @@ -299,7 +299,8 @@ EXPORT_SYMBOL_GPL(adf_flush_vf_wq);
> */
> int __init adf_init_vf_wq(void)
> {
> - adf_vf_stop_wq = alloc_workqueue("adf_vf_stop_wq", WQ_MEM_RECLAIM, 0);
> + adf_vf_stop_wq = alloc_workqueue("adf_vf_stop_wq",
> + WQ_MEM_RECLAIM | WQ_PERCPU, 0);
>
> return !adf_vf_stop_wq ? -EFAULT : 0;
> }
> --
> 2.51.1
>
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