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Message-ID: <20121002045518.GA7756@gmail.com>
Date:	Tue, 2 Oct 2012 06:55:18 +0200
From:	Ingo Molnar <mingo@...nel.org>
To:	Alexander Gordeev <agordeev@...hat.com>
Cc:	linux-kernel@...r.kernel.org, Ingo Molnar <mingo@...hat.com>,
	Thomas Gleixner <tglx@...utronix.de>,
	Bjorn Helgaas <bhelgaas@...gle.com>,
	Suresh Siddha <suresh.b.siddha@...el.com>,
	Yinghai Lu <yinghai@...nel.org>,
	Jeff Garzik <jgarzik@...ox.com>,
	Matthew Wilcox <willy@...ux.intel.com>, x86@...nel.org,
	linux-pci@...r.kernel.org, linux-ide@...r.kernel.org
Subject: Re: [PATCH v3 -tip 1/5] x86, MSI: Support multiple MSIs in presense
 of IRQ remapping


* Alexander Gordeev <agordeev@...hat.com> wrote:

> The MSI specification has several constraints in comparison with MSI-X,
> most notable of them is the inability to configure MSIs independently.
> As a result, it is impossible to dispatch interrupts from different
> queues to different CPUs. This is largely devalues the support of
> multiple MSIs in SMP systems.
> 
> Also, a necessity to allocate a contiguous block of vector numbers for
> devices capable of multiple MSIs might cause a considerable pressure on
> x86 interrupt vector allocator and could lead to fragmentation of the
> interrupt vectors space.
> 
> This patch overcomes both drawbacks in presense of IRQ remapping and
> lets devices take advantage of multiple queues and per-IRQ affinity
> assignments.
> 
> Signed-off-by: Alexander Gordeev <agordeev@...hat.com>
> ---
>  arch/x86/kernel/apic/io_apic.c |  174 +++++++++++++++++++++++++++++++++------
>  include/linux/irq.h            |    6 ++
>  kernel/irq/chip.c              |   30 +++++--
>  kernel/irq/irqdesc.c           |   31 +++++++
>  4 files changed, 206 insertions(+), 35 deletions(-)
> 
> diff --git a/arch/x86/kernel/apic/io_apic.c b/arch/x86/kernel/apic/io_apic.c
> index c265593..d5cb13c 100644
> --- a/arch/x86/kernel/apic/io_apic.c
> +++ b/arch/x86/kernel/apic/io_apic.c
> @@ -305,6 +305,11 @@ static int alloc_irq_from(unsigned int from, int node)
>  	return irq_alloc_desc_from(from, node);
>  }
>  
> +static int alloc_irqs_from(unsigned int from, unsigned int count, int node)
> +{
> +	return irq_alloc_descs_from(from, count, node);
> +}
> +
>  static void free_irq_at(unsigned int at, struct irq_cfg *cfg)
>  {
>  	free_irq_cfg(at, cfg);
> @@ -2991,37 +2996,58 @@ device_initcall(ioapic_init_ops);
>  /*
>   * Dynamic irq allocate and deallocation
>   */
> -unsigned int create_irq_nr(unsigned int from, int node)
> +unsigned int __create_irqs(unsigned int from, unsigned int count, int node)
>  {
> -	struct irq_cfg *cfg;
> +	struct irq_cfg **cfg;
>  	unsigned long flags;
> -	unsigned int ret = 0;
> -	int irq;
> +	int irq, i;
>  
>  	if (from < nr_irqs_gsi)
>  		from = nr_irqs_gsi;
>  
> -	irq = alloc_irq_from(from, node);
> -	if (irq < 0)
> -		return 0;
> -	cfg = alloc_irq_cfg(irq, node);
> -	if (!cfg) {
> -		free_irq_at(irq, NULL);
> +	cfg = kzalloc_node(count * sizeof(cfg[0]), GFP_KERNEL, node);
> +	if (!cfg)
>  		return 0;
> +
> +	irq = alloc_irqs_from(from, count, node);
> +	if (irq < 0)
> +		goto out_cfgs;
> +
> +	for (i = 0; i < count; i++) {
> +		cfg[i] = alloc_irq_cfg(irq + i, node);
> +		if (!cfg[i])
> +			goto out_irqs;
>  	}
>  
>  	raw_spin_lock_irqsave(&vector_lock, flags);
> -	if (!__assign_irq_vector(irq, cfg, apic->target_cpus()))
> -		ret = irq;
> +	for (i = 0; i < count; i++)
> +		if (__assign_irq_vector(irq + i, cfg[i], apic->target_cpus()))
> +			goto out_vecs;
>  	raw_spin_unlock_irqrestore(&vector_lock, flags);
>  
> -	if (ret) {
> -		irq_set_chip_data(irq, cfg);
> -		irq_clear_status_flags(irq, IRQ_NOREQUEST);
> -	} else {
> -		free_irq_at(irq, cfg);
> +	for (i = 0; i < count; i++) {
> +		irq_set_chip_data(irq + i, cfg[i]);
> +		irq_clear_status_flags(irq + i, IRQ_NOREQUEST);
>  	}
> -	return ret;
> +
> +	kfree(cfg);
> +	return irq;
> +
> +out_vecs:
> +	for (; i; i--)
> +		__clear_irq_vector(irq + i - 1, cfg[i - 1]);
> +	raw_spin_unlock_irqrestore(&vector_lock, flags);
> +out_irqs:
> +	for (i = 0; i < count; i++)
> +		free_irq_at(irq + i, cfg[i]);
> +out_cfgs:
> +	kfree(cfg);
> +	return 0;
> +}
> +
> +unsigned int create_irq_nr(unsigned int from, int node)
> +{
> +	return __create_irqs(from, 1, node);
>  }
>  
>  int create_irq(void)
> @@ -3054,6 +3080,27 @@ void destroy_irq(unsigned int irq)
>  	free_irq_at(irq, cfg);
>  }
>  
> +static inline void destroy_irqs(unsigned int irq, unsigned int count)
> +{
> +	unsigned int i;
> +	for (i = 0; i < count; i++)

Missing newline.

> +		destroy_irq(irq + i);
> +}
> +
> +static inline int
> +can_create_pow_of_two_irqs(unsigned int from, unsigned int count)
> +{
> +	if ((count > 1) && (count % 2))
> +		return -EINVAL;
> +
> +	for (; count; count = count / 2) {
> +		if (!irq_can_alloc_irqs(from, count))
> +			return count;
> +	}
> +
> +	return -ENOSPC;
> +}
> +
>  /*
>   * MSI message composition
>   */
> @@ -3145,18 +3192,25 @@ static struct irq_chip msi_chip = {
>  	.irq_retrigger		= ioapic_retrigger_irq,
>  };
>  
> -static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc, int irq)
> +static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc,
> +			 unsigned int irq_base, unsigned int irq_offset)
>  {
>  	struct irq_chip *chip = &msi_chip;
>  	struct msi_msg msg;
> +	unsigned int irq = irq_base + irq_offset;
>  	int ret;
>  
>  	ret = msi_compose_msg(dev, irq, &msg, -1);
>  	if (ret < 0)
>  		return ret;
>  
> -	irq_set_msi_desc(irq, msidesc);
> -	write_msi_msg(irq, &msg);
> +	irq_set_msi_desc_off(irq_base, irq_offset, msidesc);
> +
> +	/* MSI-X message is written per-IRQ, the offset is always 0.
> +	 * MSI message denotes a contiguous group of IRQs, written for 0th IRQ.
> +	 */

Please use the customary (multi-line) comment style:

  /*
   * Comment .....
   * ...... goes here.
   */

specified in Documentation/CodingStyle.


> +	if (!irq_offset)
> +		write_msi_msg(irq, &msg);
>  
>  	if (irq_remapped(irq_get_chip_data(irq))) {
>  		irq_set_status_flags(irq, IRQ_MOVE_PCNTXT);
> @@ -3170,16 +3224,12 @@ static int setup_msi_irq(struct pci_dev *dev, struct msi_desc *msidesc, int irq)
>  	return 0;
>  }
>  
> -int native_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
> +int setup_msix_irqs(struct pci_dev *dev, int nvec)
>  {
>  	int node, ret, sub_handle, index = 0;
>  	unsigned int irq, irq_want;
>  	struct msi_desc *msidesc;
>  
> -	/* x86 doesn't support multiple MSI yet */
> -	if (type == PCI_CAP_ID_MSI && nvec > 1)
> -		return 1;
> -
>  	node = dev_to_node(&dev->dev);
>  	irq_want = nr_irqs_gsi;
>  	sub_handle = 0;
> @@ -3208,7 +3258,7 @@ int native_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
>  				goto error;
>  		}
>  no_ir:
> -		ret = setup_msi_irq(dev, msidesc, irq);
> +		ret = setup_msi_irq(dev, msidesc, irq, 0);
>  		if (ret < 0)
>  			goto error;
>  		sub_handle++;
> @@ -3220,6 +3270,76 @@ error:
>  	return ret;
>  }
>  
> +int setup_msi_irqs(struct pci_dev *dev, int nvec)
> +{
> +	int node, ret, sub_handle, index = 0;
> +	unsigned int irq;
> +	struct msi_desc *msidesc;
> +
> +	if (nvec > 1 && !irq_remapping_enabled)
> +		return 1;
> +
> +	nvec = __roundup_pow_of_two(nvec);
> +	ret = can_create_pow_of_two_irqs(nr_irqs_gsi, nvec);
> +	if (ret != nvec)
> +		return ret;
> +
> +	WARN_ON(!list_is_singular(&dev->msi_list));
> +	msidesc = list_entry(dev->msi_list.next, struct msi_desc, list);
> +	WARN_ON(msidesc->irq);
> +	WARN_ON(msidesc->msi_attrib.multiple);
> +
> +	node = dev_to_node(&dev->dev);
> +	irq = __create_irqs(nr_irqs_gsi, nvec, node);
> +	if (irq == 0)
> +		return -ENOSPC;
> +
> +	if (!irq_remapping_enabled) {
> +		ret = setup_msi_irq(dev, msidesc, irq, 0);
> +		if (ret < 0)
> +			goto error;
> +		return 0;
> +	}
> +
> +	msidesc->msi_attrib.multiple = ilog2(nvec);
> +	for (sub_handle = 0; sub_handle < nvec; sub_handle++) {
> +		if (!sub_handle) {
> +			index = msi_alloc_remapped_irq(dev, irq, nvec);
> +			if (index < 0) {
> +				ret = index;
> +				goto error;
> +			}
> +		} else {
> +			ret = msi_setup_remapped_irq(dev, irq + sub_handle,
> +						     index, sub_handle);
> +			if (ret < 0)
> +				goto error;
> +		}
> +		ret = setup_msi_irq(dev, msidesc, irq, sub_handle);
> +		if (ret < 0)
> +			goto error;
> +	}
> +	return 0;
> +
> +error:
> +	destroy_irqs(irq, nvec);
> +
> +	/* Restore altered MSI descriptor fields and prevent just destroyed
> +	 * IRQs from tearing down again in default_teardown_msi_irqs()
> +	 */

Ditto.

> +	msidesc->irq = 0;
> +	msidesc->msi_attrib.multiple = 0;
> +
> +	return ret;
> +}
> +
> +int native_setup_msi_irqs(struct pci_dev *dev, int nvec, int type)
> +{
> +	if (type == PCI_CAP_ID_MSI)
> +		return setup_msi_irqs(dev, nvec);
> +	return setup_msix_irqs(dev, nvec);
> +}
> +
>  void native_teardown_msi_irq(unsigned int irq)
>  {
>  	destroy_irq(irq);
> diff --git a/include/linux/irq.h b/include/linux/irq.h
> index 216b0ba..c3ba39f 100644
> --- a/include/linux/irq.h
> +++ b/include/linux/irq.h
> @@ -522,6 +522,8 @@ extern int irq_set_handler_data(unsigned int irq, void *data);
>  extern int irq_set_chip_data(unsigned int irq, void *data);
>  extern int irq_set_irq_type(unsigned int irq, unsigned int type);
>  extern int irq_set_msi_desc(unsigned int irq, struct msi_desc *entry);
> +extern int irq_set_msi_desc_off(unsigned int irq_base, unsigned int irq_offset,
> +				struct msi_desc *entry);
>  extern struct irq_data *irq_get_irq_data(unsigned int irq);
>  
>  static inline struct irq_chip *irq_get_chip(unsigned int irq)
> @@ -584,8 +586,12 @@ int __irq_alloc_descs(int irq, unsigned int from, unsigned int cnt, int node,
>  #define irq_alloc_desc_from(from, node)		\
>  	irq_alloc_descs(-1, from, 1, node)
>  
> +#define irq_alloc_descs_from(from, cnt, node)	\
> +	irq_alloc_descs(-1, from, cnt, node)
> +

Please use inlines instead of macros. Might transform the one 
above it as well in the process.

>  void irq_free_descs(unsigned int irq, unsigned int cnt);
>  int irq_reserve_irqs(unsigned int from, unsigned int cnt);
> +int irq_can_alloc_irqs(unsigned int from, unsigned int cnt);
>  
>  static inline void irq_free_desc(unsigned int irq)
>  {
> diff --git a/kernel/irq/chip.c b/kernel/irq/chip.c
> index 57d86d0..2230389 100644
> --- a/kernel/irq/chip.c
> +++ b/kernel/irq/chip.c
> @@ -90,27 +90,41 @@ int irq_set_handler_data(unsigned int irq, void *data)
>  EXPORT_SYMBOL(irq_set_handler_data);
>  
>  /**
> - *	irq_set_msi_desc - set MSI descriptor data for an irq
> - *	@irq:	Interrupt number
> - *	@entry:	Pointer to MSI descriptor data
> + *	irq_set_msi_desc_off - set MSI descriptor data for an irq at offset
> + *	@irq_base:	Interrupt number base
> + *	@irq_offset:	Interrupt number offset
> + *	@entry:		Pointer to MSI descriptor data
>   *
> - *	Set the MSI descriptor entry for an irq
> + *	Set the MSI descriptor entry for an irq at offset
>   */
> -int irq_set_msi_desc(unsigned int irq, struct msi_desc *entry)
> +int irq_set_msi_desc_off(unsigned int irq_base, unsigned int irq_offset,
> +			 struct msi_desc *entry)
>  {
>  	unsigned long flags;
> -	struct irq_desc *desc = irq_get_desc_lock(irq, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
> +	struct irq_desc *desc = irq_get_desc_lock(irq_base + irq_offset, &flags, IRQ_GET_DESC_CHECK_GLOBAL);
>  
>  	if (!desc)
>  		return -EINVAL;
>  	desc->irq_data.msi_desc = entry;
> -	if (entry)
> -		entry->irq = irq;
> +	if (entry && !irq_offset)
> +		entry->irq = irq_base;
>  	irq_put_desc_unlock(desc, flags);
>  	return 0;
>  }
>  
>  /**
> + *	irq_set_msi_desc - set MSI descriptor data for an irq
> + *	@irq:	Interrupt number
> + *	@entry:	Pointer to MSI descriptor data
> + *
> + *	Set the MSI descriptor entry for an irq
> + */
> +int irq_set_msi_desc(unsigned int irq, struct msi_desc *entry)
> +{
> +	return irq_set_msi_desc_off(irq, 0, entry);
> +}
> +
> +/**
>   *	irq_set_chip_data - set irq chip data for an irq
>   *	@irq:	Interrupt number
>   *	@data:	Pointer to chip specific data
> diff --git a/kernel/irq/irqdesc.c b/kernel/irq/irqdesc.c
> index 192a302..8287b78 100644
> --- a/kernel/irq/irqdesc.c
> +++ b/kernel/irq/irqdesc.c
> @@ -210,6 +210,13 @@ static int irq_expand_nr_irqs(unsigned int nr)
>  	return 0;
>  }
>  
> +static int irq_can_expand_nr_irqs(unsigned int nr)
> +{
> +	if (nr > IRQ_BITMAP_BITS)
> +		return -ENOMEM;
> +	return 0;
> +}
> +
>  int __init early_irq_init(void)
>  {
>  	int i, initcnt, node = first_online_node;
> @@ -414,6 +421,30 @@ int irq_reserve_irqs(unsigned int from, unsigned int cnt)
>  }
>  
>  /**
> + * irq_can_alloc_irqs - checks if a range of irqs could be allocated
> + * @from:	check from irq number
> + * @cnt:	number of irqs to check
> + *
> + * Returns 0 on success or an appropriate error code
> + */
> +int irq_can_alloc_irqs(unsigned int from, unsigned int cnt)
> +{
> +	unsigned int start;
> +	int ret = 0;
> +
> +	if (!cnt)
> +		return -EINVAL;
> +
> +	mutex_lock(&sparse_irq_lock);
> +	start = bitmap_find_next_zero_area(allocated_irqs, IRQ_BITMAP_BITS,
> +					   from, cnt, 0);
> +	mutex_unlock(&sparse_irq_lock);
> +	if (start + cnt > nr_irqs)
> +		ret = irq_can_expand_nr_irqs(start + cnt);
> +	return ret;

How is this supposed to work wrt. races?

Thanks,

	Ingo
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