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Message-ID: <6dc6642a-1e7c-f111-1fa2-be54826ecef6@huawei.com>
Date: Mon, 29 May 2023 15:57:07 +0800
From: "Liao, Chang" <liaochang1@...wei.com>
To: Shanker Donthineni <sdonthineni@...dia.com>,
Thomas Gleixner <tglx@...utronix.de>,
Marc Zyngier <maz@...nel.org>
CC: Sebastian Andrzej Siewior <bigeasy@...utronix.de>,
Michael Walle <michael@...le.cc>,
<linux-kernel@...r.kernel.org>, Vikram Sethi <vsethi@...dia.com>,
Jason Sequeira <jsequeira@...dia.com>
Subject: Re: [PATCH v5 1/3] genirq: Use hlist for managing resend handlers
Hi, Shanker
在 2023/5/19 21:49, Shanker Donthineni 写道:
> The current implementation utilizes a bitmap for managing IRQ resend
> handlers, which is allocated based on the SPARSE_IRQ/NR_IRQS macros.
> However, this method may not efficiently utilize memory during runtime,
> particularly when IRQ_BITMAP_BITS is large.
>
> Address this issue by using the hlist to manage IRQ resend handlers
> instead of relying on a static bitmap memory allocation. Additionally,
> a new function, clear_irq_resend(), is introduced and called from
> irq_shutdown to ensure a graceful teardown of the interrupt.
>
> Signed-off-by: Shanker Donthineni <sdonthineni@...dia.com>
> ---
> include/linux/irqdesc.h | 3 +++
> kernel/irq/chip.c | 1 +
> kernel/irq/internals.h | 2 ++
> kernel/irq/irqdesc.c | 2 ++
> kernel/irq/resend.c | 47 ++++++++++++++++++++++++++---------------
> 5 files changed, 38 insertions(+), 17 deletions(-)
>
> diff --git a/include/linux/irqdesc.h b/include/linux/irqdesc.h
> index 844a8e30e6de..d9451d456a73 100644
> --- a/include/linux/irqdesc.h
> +++ b/include/linux/irqdesc.h
> @@ -102,6 +102,9 @@ struct irq_desc {
> int parent_irq;
> struct module *owner;
> const char *name;
> +#ifdef CONFIG_HARDIRQS_SW_RESEND
> + struct hlist_node resend_node;
> +#endif
> } ____cacheline_internodealigned_in_smp;
Although there is no documented rule that limits the change of the KABI
struct irq_desc, it is still better to keep the irq_desc definition stable.
>
> #ifdef CONFIG_SPARSE_IRQ
> diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> index 49e7bc871fec..2eac5532c3c8 100644
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -306,6 +306,7 @@ static void __irq_disable(struct irq_desc *desc, bool mask);
> void irq_shutdown(struct irq_desc *desc)
> {
> if (irqd_is_started(&desc->irq_data)) {
> + clear_irq_resend(desc);
> desc->depth = 1;
> if (desc->irq_data.chip->irq_shutdown) {
> desc->irq_data.chip->irq_shutdown(&desc->irq_data);
> diff --git a/kernel/irq/internals.h b/kernel/irq/internals.h
> index 5fdc0b557579..51fc8c497c22 100644
> --- a/kernel/irq/internals.h
> +++ b/kernel/irq/internals.h
> @@ -113,6 +113,8 @@ irqreturn_t handle_irq_event(struct irq_desc *desc);
>
> /* Resending of interrupts :*/
> int check_irq_resend(struct irq_desc *desc, bool inject);
> +void clear_irq_resend(struct irq_desc *desc);
> +void irq_resend_init(struct irq_desc *desc);
> bool irq_wait_for_poll(struct irq_desc *desc);
> void __irq_wake_thread(struct irq_desc *desc, struct irqaction *action);
>
> diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> index 240e145e969f..b401b89b226a 100644
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -415,6 +415,7 @@ static struct irq_desc *alloc_desc(int irq, int node, unsigned int flags,
> desc_set_defaults(irq, desc, node, affinity, owner);
> irqd_set(&desc->irq_data, flags);
> kobject_init(&desc->kobj, &irq_kobj_type);
> + irq_resend_init(desc);
>
> return desc;
>
> @@ -581,6 +582,7 @@ int __init early_irq_init(void)
> mutex_init(&desc[i].request_mutex);
> init_waitqueue_head(&desc[i].wait_for_threads);
> desc_set_defaults(i, &desc[i], node, NULL, NULL);
> + irq_resend_init(desc);
> }
> return arch_early_irq_init();
> }
> diff --git a/kernel/irq/resend.c b/kernel/irq/resend.c
> index 0c46e9fe3a89..edec335c0a7a 100644
> --- a/kernel/irq/resend.c
> +++ b/kernel/irq/resend.c
> @@ -21,8 +21,9 @@
>
> #ifdef CONFIG_HARDIRQS_SW_RESEND
>
> -/* Bitmap to handle software resend of interrupts: */
> -static DECLARE_BITMAP(irqs_resend, IRQ_BITMAP_BITS);
> +/* hlist_head to handle software resend of interrupts: */
> +static HLIST_HEAD(irq_resend_list);
> +static DEFINE_RAW_SPINLOCK(irq_resend_lock);
What is the benefit of using hlist here? If you want to enjoy the
low latency of querying elements by key, you must define a hlist table
with a reasonable number of buckets. Otherwise, I don't think the time
complexity of hlist is better than a regular double-linked list, right?
>
> /*
> * Run software resends of IRQ's
> @@ -30,18 +31,17 @@ static DECLARE_BITMAP(irqs_resend, IRQ_BITMAP_BITS);
> static void resend_irqs(struct tasklet_struct *unused)
> {
> struct irq_desc *desc;
> - int irq;
> -
> - while (!bitmap_empty(irqs_resend, nr_irqs)) {
> - irq = find_first_bit(irqs_resend, nr_irqs);
> - clear_bit(irq, irqs_resend);
> - desc = irq_to_desc(irq);
> - if (!desc)
> - continue;
> - local_irq_disable();
> +
> + raw_spin_lock_irq(&irq_resend_lock);
> + while (!hlist_empty(&irq_resend_list)) {> + desc = hlist_entry(irq_resend_list.first, struct irq_desc,
> + resend_node);
> + hlist_del_init(&desc->resend_node);
> + raw_spin_unlock(&irq_resend_lock);
> desc->handle_irq(desc);
> - local_irq_enable();
> + raw_spin_lock(&irq_resend_lock);
> }
> + raw_spin_unlock_irq(&irq_resend_lock);
> }
>
> /* Tasklet to handle resend: */
> @@ -49,8 +49,6 @@ static DECLARE_TASKLET(resend_tasklet, resend_irqs);
>
> static int irq_sw_resend(struct irq_desc *desc)
> {
> - unsigned int irq = irq_desc_get_irq(desc);
> -
> /*
> * Validate whether this interrupt can be safely injected from
> * non interrupt context
> @@ -70,16 +68,31 @@ static int irq_sw_resend(struct irq_desc *desc)
> */
> if (!desc->parent_irq)
> return -EINVAL;
> - irq = desc->parent_irq;
Why delete this code?
> }
>
> - /* Set it pending and activate the softirq: */
> - set_bit(irq, irqs_resend);
> + /* Add to resend_list and activate the softirq: */
> + raw_spin_lock(&irq_resend_lock);
> + hlist_add_head(&desc->resend_node, &irq_resend_list);
> + raw_spin_unlock(&irq_resend_lock);
Do you conside a situation where irq_sw_resend() is running on two CPUs concurrently?
If so, the same desc could be added into irq_resend_list twice by mistake.
> tasklet_schedule(&resend_tasklet);
> return 0;
> }
>
> +void clear_irq_resend(struct irq_desc *desc)
> +{
> + raw_spin_lock(&irq_resend_lock);
> + hlist_del_init(&desc->resend_node);
> + raw_spin_unlock(&irq_resend_lock);
> +}
> +
> +void irq_resend_init(struct irq_desc *desc)
> +{
> + INIT_HLIST_NODE(&desc->resend_node);
> +}
> #else
> +void clear_irq_resend(struct irq_desc *desc) {}
> +void irq_resend_init(struct irq_desc *desc) {}
> +
> static int irq_sw_resend(struct irq_desc *desc)
> {
> return -EINVAL;
--
BR
Liao, Chang
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