Re: [PATCH] xen: do not clear and mask evtchns in__xen_evtchn_do_upcall

[Konrad Rzeszutek Wilk]

On Tue, Mar 29, 2011 at 03:15:07PM +0100, Stefano Stabellini wrote:
> xen: do not clear and mask evtchns in __xen_evtchn_do_upcall
> 
> Switch virqs and pirqs that don't need EOI (in Xen acktype ==
   ^^                   ^^
Swap                     irq sub-handlers? 
> ACKTYPE_NONE, that means the machine irq is actually edge)

And where is the ACKTYPE_NONE? Is that a Xen hypervisor thing?
Ah yes. It looks like soo. Perhaps you should rephrase that
and explain what ACKTYPE_NONE is.

I think for these patches the more copious the comments are
the better - in case we want to revisit this in next quarter.
> to handle_edge_irq.
> 
> Use handle_fasteoi_irq for pirqs that need eoi (they generally
> correspond to level triggered irqs), no risk in loosing interrupts
> because we have to EOI the irq anyway.

Can you include an URL to explain what EOI/level/edge interrupts
are? Maybe the correct page in the Intel manual?

I wish there was a table explaining when/or what type of eoi
you need per different type of interrupts. B/c it looks like
you can do EOI for edge-type interrupts (ISA), but not for
MSI/MSI-X ones.
> 
> This change has the following benefits:
> 
> - it uses the very same handlers that Linux would use on native for the
> same irqs;

Can you expand? As in for the GSI? Or for the MSI/MSI-X?

> 
> - it uses these handlers in the same way Linux would use them: it let
> Linux mask\unmask and ack the irq when Linux want to mask\unmask and ack
> the irq;
> 
> Signed-off-by: Stefano Stabellini <stefano.stabellini@xxxxxxxxxxxxx>
> 
> diff --git a/drivers/xen/events.c b/drivers/xen/events.c
> index 02b5a9c..4f15dde 100644
> --- a/drivers/xen/events.c
> +++ b/drivers/xen/events.c
> @@ -118,6 +118,8 @@ static DEFINE_PER_CPU(unsigned long [NR_EVENT_CHANNELS/BITS_PER_LONG],
>  static struct irq_chip xen_dynamic_chip;
>  static struct irq_chip xen_percpu_chip;
>  static struct irq_chip xen_pirq_chip;
> +static void enable_dynirq(struct irq_data *data);
> +static void disable_dynirq(struct irq_data *data);
>  
>  /* Get info for IRQ */
>  static struct irq_info *info_for_irq(unsigned irq)
> @@ -473,16 +475,6 @@ static void xen_free_irq(unsigned irq)
>  	irq_free_desc(irq);
>  }
>  
> -static void pirq_unmask_notify(int irq)
> -{
> -	struct physdev_eoi eoi = { .irq = pirq_from_irq(irq) };
> -
> -	if (unlikely(pirq_needs_eoi(irq))) {
> -		int rc = HYPERVISOR_physdev_op(PHYSDEVOP_eoi, &eoi);
> -		WARN_ON(rc);
> -	}
> -}
> -
>  static void pirq_query_unmask(int irq)
>  {
>  	struct physdev_irq_status_query irq_status;
> @@ -506,6 +498,30 @@ static bool probing_irq(int irq)
>  	return desc && desc->action == NULL;
>  }
>  
> +static void eoi_pirq(struct irq_data *data)
> +{
> +	int evtchn = evtchn_from_irq(data->irq);
> + 	struct irq_info *info = info_for_irq(data->irq);
> + 	struct physdev_eoi eoi = { .irq = info->u.pirq.gsi };

No pirq?
> +	int rc = 0;
> +
> +	move_native_irq(data->irq);
> +
> +	if (VALID_EVTCHN(evtchn))
> +		clear_evtchn(evtchn);
> +
> +	if (pirq_needs_eoi(data->irq)) {

Hm, you are using the Linux IRQ here, not the PIRQ value.

> +		rc = HYPERVISOR_physdev_op(PHYSDEVOP_eoi, &eoi);
> +		WARN_ON(rc);
> +	}
> +}
> +
> +static void mask_ack_pirq(struct irq_data *data)
> +{
> +	disable_dynirq(data);
> +	eoi_pirq(data);
> +}
> + 
>  static unsigned int __startup_pirq(unsigned int irq)
>  {
>  	struct evtchn_bind_pirq bind_pirq;
> @@ -539,7 +555,7 @@ static unsigned int __startup_pirq(unsigned int irq)
>  
>  out:
>  	unmask_evtchn(evtchn);
> -	pirq_unmask_notify(irq);
> +	eoi_pirq(irq_get_irq_data(irq));
>  
>  	return 0;
>  }
> @@ -572,27 +588,6 @@ static void shutdown_pirq(struct irq_data *data)
>  	info->evtchn = 0;
>  }
>  
> -static void enable_pirq(struct irq_data *data)
> -{
> -	startup_pirq(data);
> -}
> -
> -static void disable_pirq(struct irq_data *data)
> -{
> -}
> -
> -static void ack_pirq(struct irq_data *data)
> -{
> -	int evtchn = evtchn_from_irq(data->irq);
> -
> -	move_native_irq(data->irq);
> -
> -	if (VALID_EVTCHN(evtchn)) {
> -		mask_evtchn(evtchn);
> -		clear_evtchn(evtchn);
> -	}
> -}
> -
>  static int find_irq_by_gsi(unsigned gsi)
>  {
>  	struct irq_info *info;
> @@ -639,9 +634,6 @@ int xen_bind_pirq_gsi_to_irq(unsigned gsi,
>  	if (irq < 0)
>  		goto out;
>  
> -	set_irq_chip_and_handler_name(irq, &xen_pirq_chip,
> -				      handle_level_irq, name);
> -
>  	irq_op.irq = irq;
>  	irq_op.vector = 0;
>  
> @@ -658,6 +650,14 @@ int xen_bind_pirq_gsi_to_irq(unsigned gsi,
>  	xen_irq_info_pirq_init(irq, 0, pirq, gsi, irq_op.vector,
>  			       shareable ? PIRQ_SHAREABLE : 0);
>  
> +	pirq_query_unmask(irq);
> +	if (pirq_needs_eoi(irq))
> +		set_irq_chip_and_handler_name(irq, &xen_pirq_chip,
> +				handle_fasteoi_irq, name);
> +	else
> +		set_irq_chip_and_handler_name(irq, &xen_pirq_chip,
> +				handle_edge_irq, name);

OK. You need a big comment about this in the code. Explain
why this is happening. B/c if you look at this from code
it seems like wrong thing to do for gsi's (as in you would
think handle_level_irq would the right choice).

> +
>  out:
>  	spin_unlock(&irq_mapping_update_lock);
>  
> @@ -691,7 +691,7 @@ int xen_bind_pirq_msi_to_irq(struct pci_dev *dev, struct msi_desc *msidesc,
>  		goto out;
>  
>  	set_irq_chip_and_handler_name(irq, &xen_pirq_chip,
> -				      handle_level_irq, name);
> +				      handle_edge_irq, name);
>  
>  	xen_irq_info_pirq_init(irq, 0, pirq, 0, vector, 0);
>  	ret = irq_set_msi_desc(irq, msidesc);
> @@ -773,7 +773,7 @@ int bind_evtchn_to_irq(unsigned int evtchn)
>  			goto out;
>  
>  		set_irq_chip_and_handler_name(irq, &xen_dynamic_chip,
> -					      handle_fasteoi_irq, "event");
> +					      handle_edge_irq, "event");
>  
>  		xen_irq_info_evtchn_init(irq, evtchn);
>  	}
> @@ -1181,9 +1181,6 @@ static void __xen_evtchn_do_upcall(void)
>  				port = (word_idx * BITS_PER_LONG) + bit_idx;
>  				irq = evtchn_to_irq[port];
>  
> -				mask_evtchn(port);
> -				clear_evtchn(port);
> -
>  				if (irq != -1) {
>  					desc = irq_to_desc(irq);
>  					if (desc)
> @@ -1339,12 +1336,18 @@ static void ack_dynirq(struct irq_data *data)
>  {
>  	int evtchn = evtchn_from_irq(data->irq);
>  
> -	move_masked_irq(data->irq);
> +	move_native_irq(data->irq);
>  
>  	if (VALID_EVTCHN(evtchn))
> -		unmask_evtchn(evtchn);
> +		clear_evtchn(evtchn);
>  }
>  
> +static void mask_ack_dynirq(struct irq_data *data)
> +{
> +	disable_dynirq(data);
> +	ack_dynirq(data);
> +}
> + 
>  static int retrigger_dynirq(struct irq_data *data)
>  {
>  	int evtchn = evtchn_from_irq(data->irq);
> @@ -1533,11 +1536,12 @@ void xen_irq_resume(void)
>  static struct irq_chip xen_dynamic_chip __read_mostly = {
>  	.name			= "xen-dyn",
>  
> -	.irq_disable		= disable_dynirq,
>  	.irq_mask		= disable_dynirq,
>  	.irq_unmask		= enable_dynirq,
>  
> -	.irq_eoi		= ack_dynirq,
> +	.irq_ack		= ack_dynirq,
> +	.irq_mask_ack		= mask_ack_dynirq,
> +

Do we need to this for percpu handler? 
>  	.irq_set_affinity	= set_affinity_irq,
>  	.irq_retrigger		= retrigger_dynirq,
>  };
> @@ -1548,13 +1552,12 @@ static struct irq_chip xen_pirq_chip __read_mostly = {
>  	.irq_startup		= startup_pirq,
>  	.irq_shutdown		= shutdown_pirq,
>  
> -	.irq_enable		= enable_pirq,
> -	.irq_unmask		= enable_pirq,
> -
> -	.irq_disable		= disable_pirq,
> -	.irq_mask		= disable_pirq,
> +	.irq_mask		= disable_dynirq,
> +	.irq_unmask		= enable_dynirq,
>  
> -	.irq_ack		= ack_pirq,
> +	.irq_ack		= eoi_pirq,
> +	.irq_eoi		= eoi_pirq,
> +	.irq_mask_ack		= mask_ack_pirq,
>  
>  	.irq_set_affinity	= set_affinity_irq,
>  
--
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