thr3ads.net - Linux Virtualization - [PATCH RFC] virtio-pci: share config interrupt between virtio devices [Sep 2014]

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Amos Kong

2014-Sep-01 05:41 UTC

[PATCH RFC] virtio-pci: share config interrupt between virtio devices

One VM only has 128 msix interrupt, virtio-config interrupt
has less workload. This patch shares one normal interrupt
for configuration between virtio devices.

Signed-off-by: Amos Kong <akong at redhat.com>
---
 drivers/virtio/virtio_pci.c | 41 ++++++++++++++++-------------------------
 1 file changed, 16 insertions(+), 25 deletions(-)

diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
index 3d1463c..b1263b3 100644
--- a/drivers/virtio/virtio_pci.c
+++ b/drivers/virtio/virtio_pci.c
@@ -52,6 +52,7 @@ struct virtio_pci_device
 	/* Name strings for interrupts. This size should be enough,
 	 * and I'm too lazy to allocate each name separately. */
 	char (*msix_names)[256];
+	char config_msix_name[256];
 	/* Number of available vectors */
 	unsigned msix_vectors;
 	/* Vectors allocated, excluding per-vq vectors if any */
@@ -282,12 +283,6 @@ static void vp_free_vectors(struct virtio_device *vdev)
 			free_cpumask_var(vp_dev->msix_affinity_masks[i]);
 
 	if (vp_dev->msix_enabled) {
-		/* Disable the vector used for configuration */
-		iowrite16(VIRTIO_MSI_NO_VECTOR,
-			  vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
-		/* Flush the write out to device */
-		ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
-
 		pci_disable_msix(vp_dev->pci_dev);
 		vp_dev->msix_enabled = 0;
 	}
@@ -339,24 +334,18 @@ static int vp_request_msix_vectors(struct virtio_device
*vdev, int nvectors,
 		goto error;
 	vp_dev->msix_enabled = 1;
 
-	/* Set the vector used for configuration */
-	v = vp_dev->msix_used_vectors;
-	snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
+	/* Set shared IRQ for configuration */
+	snprintf(vp_dev->config_msix_name, sizeof(*vp_dev->msix_names),
 		 "%s-config", name);
-	err = request_irq(vp_dev->msix_entries[v].vector,
-			  vp_config_changed, 0, vp_dev->msix_names[v],
+	err = request_irq(vp_dev->pci_dev->irq,
+			  vp_config_changed,
+			  IRQF_SHARED,
+			  vp_dev->config_msix_name,
 			  vp_dev);
-	if (err)
-		goto error;
-	++vp_dev->msix_used_vectors;
-
-	iowrite16(v, vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
-	/* Verify we had enough resources to assign the vector */
-	v = ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
-	if (v == VIRTIO_MSI_NO_VECTOR) {
-		err = -EBUSY;
+	if (!err)
+		vp_dev->intx_enabled = 1;
+	else
 		goto error;
-	}
 
 	if (!per_vq_vectors) {
 		/* Shared vector for all VQs */
@@ -535,14 +524,16 @@ static int vp_try_to_find_vqs(struct virtio_device *vdev,
unsigned nvqs,
 			goto error_request;
 	} else {
 		if (per_vq_vectors) {
-			/* Best option: one for change interrupt, one per vq. */
-			nvectors = 1;
+			/* Best option: one normal interrupt for change,
+			   one msix per vq. */
+			nvectors = 0;
 			for (i = 0; i < nvqs; ++i)
 				if (callbacks[i])
 					++nvectors;
 		} else {
-			/* Second best: one for change, shared for all vqs. */
-			nvectors = 2;
+			/* Second best: one normal interrupt for
+			   change, share one msix for all vqs. */
+			nvectors = 1;
 		}
 
 		err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);
-- 
1.9.3

Michael S. Tsirkin

2014-Sep-01 06:37 UTC

head link

[PATCH RFC] virtio-pci: share config interrupt between virtio devices

On Mon, Sep 01, 2014 at 01:41:54PM +0800, Amos Kong
wrote:> One VM only has 128 msix interrupt, virtio-config interrupt
> has less workload. This patch shares one normal interrupt
normal == INT#x? Please don't call it normal. The proper name is
"legacy INT#x".

So you are trying to use legacy INT#x at the same time
with MSI-X?  This does not work: the PCI spec says:
	While enabled for MSI or MSI-X
	operation, a function is prohibited from using its INTx# pin (if
	implemented) to request
	service (MSI, MSI-X, and INTx# are mutually exclusive).

does the patch work for you? If it does it might be a (minor) spec
violation in kvm.

Besides, INT#x really leads to terrible performance because
sharing is forced even if there aren't many devices.

Why do we need INT#x?
How about setting IRQF_SHARED for the config interrupt
while using MSI-X? You'd have to read ISR to check that the interrupt was
intended for your device.

> for configuration between virtio devices.
> 
> Signed-off-by: Amos Kong <akong at redhat.com>
> ---
>  drivers/virtio/virtio_pci.c | 41 ++++++++++++++++-------------------------
>  1 file changed, 16 insertions(+), 25 deletions(-)
> 
> diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
> index 3d1463c..b1263b3 100644
> --- a/drivers/virtio/virtio_pci.c
> +++ b/drivers/virtio/virtio_pci.c
> @@ -52,6 +52,7 @@ struct virtio_pci_device
>  	/* Name strings for interrupts. This size should be enough,
>  	 * and I'm too lazy to allocate each name separately. */
>  	char (*msix_names)[256];
> +	char config_msix_name[256];
>  	/* Number of available vectors */
>  	unsigned msix_vectors;
>  	/* Vectors allocated, excluding per-vq vectors if any */
> @@ -282,12 +283,6 @@ static void vp_free_vectors(struct virtio_device
*vdev)
>  			free_cpumask_var(vp_dev->msix_affinity_masks[i]);
>  
>  	if (vp_dev->msix_enabled) {
> -		/* Disable the vector used for configuration */
> -		iowrite16(VIRTIO_MSI_NO_VECTOR,
> -			  vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> -		/* Flush the write out to device */
> -		ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> -
>  		pci_disable_msix(vp_dev->pci_dev);
>  		vp_dev->msix_enabled = 0;
>  	}
> @@ -339,24 +334,18 @@ static int vp_request_msix_vectors(struct
virtio_device *vdev, int nvectors,
>  		goto error;
>  	vp_dev->msix_enabled = 1;
>  
> -	/* Set the vector used for configuration */
> -	v = vp_dev->msix_used_vectors;
> -	snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
> +	/* Set shared IRQ for configuration */
> +	snprintf(vp_dev->config_msix_name, sizeof(*vp_dev->msix_names),
>  		 "%s-config", name);
> -	err = request_irq(vp_dev->msix_entries[v].vector,
> -			  vp_config_changed, 0, vp_dev->msix_names[v],
> +	err = request_irq(vp_dev->pci_dev->irq,
> +			  vp_config_changed,
> +			  IRQF_SHARED,
> +			  vp_dev->config_msix_name,
>  			  vp_dev);
> -	if (err)
> -		goto error;
> -	++vp_dev->msix_used_vectors;
> -
> -	iowrite16(v, vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> -	/* Verify we had enough resources to assign the vector */
> -	v = ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> -	if (v == VIRTIO_MSI_NO_VECTOR) {
> -		err = -EBUSY;
> +	if (!err)
> +		vp_dev->intx_enabled = 1;
> +	else
>  		goto error;
> -	}
>  
>  	if (!per_vq_vectors) {
>  		/* Shared vector for all VQs */
> @@ -535,14 +524,16 @@ static int vp_try_to_find_vqs(struct virtio_device
*vdev, unsigned nvqs,
>  			goto error_request;
>  	} else {
>  		if (per_vq_vectors) {
> -			/* Best option: one for change interrupt, one per vq. */
> -			nvectors = 1;
> +			/* Best option: one normal interrupt for change,
> +			   one msix per vq. */
> +			nvectors = 0;
>  			for (i = 0; i < nvqs; ++i)
>  				if (callbacks[i])
>  					++nvectors;
>  		} else {
> -			/* Second best: one for change, shared for all vqs. */
> -			nvectors = 2;
> +			/* Second best: one normal interrupt for
> +			   change, share one msix for all vqs. */
> +			nvectors = 1;
>  		}
>  
>  		err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);
> -- 
> 1.9.3

Amos Kong

2014-Sep-01 07:58 UTC

head link

[PATCH RFC] virtio-pci: share config interrupt between virtio devices

On Mon, Sep 01, 2014 at 09:37:30AM +0300, Michael S. Tsirkin
wrote:>
Hi Michael,
> On Mon, Sep 01, 2014 at 01:41:54PM +0800, Amos Kong wrote:
> > One VM only has 128 msix interrupt, virtio-config interrupt
> > has less workload. This patch shares one normal interrupt
Thanks for your quick reply.
> normal == INT#x? Please don't call it normal. The proper name is
> "legacy INT#x". 
OK
> So you are trying to use legacy INT#x at the same time
> with MSI-X?  This does not work: the PCI spec says:
> 	While enabled for MSI or MSI-X
> 	operation, a function is prohibited from using its INTx# pin (if
> 	implemented) to request
> 	service (MSI, MSI-X, and INTx# are mutually exclusive).
It means we can't use interrupt and triggered-interrupt together for
one PCI device. I will study this problem.
 > does the patch work for you? If it does it might be a (minor) spec
> violation in kvm.
I did some basic testing (multiple nics, scp, ping, etc), it works.
 > Besides, INT#x really leads to terrible performance because
> sharing is forced even if there aren't many devices.
> 
> Why do we need INT#x?
> How about setting IRQF_SHARED for the config interrupt
> while using MSI-X?
> You'd have to read ISR to check that the interrupt was
> intended for your device. 
I have a draft patch to share one MSI-X for all virtio-config, it has
some problem in hotplugging devices. I will continue this way.
 > > for configuration between virtio devices.
> > 
> > Signed-off-by: Amos Kong <akong at redhat.com>
> > ---
> >  drivers/virtio/virtio_pci.c | 41
++++++++++++++++-------------------------
> >  1 file changed, 16 insertions(+), 25 deletions(-)
> > 
> > diff --git a/drivers/virtio/virtio_pci.c b/drivers/virtio/virtio_pci.c
> > index 3d1463c..b1263b3 100644
> > --- a/drivers/virtio/virtio_pci.c
> > +++ b/drivers/virtio/virtio_pci.c
> > @@ -52,6 +52,7 @@ struct virtio_pci_device
> >  	/* Name strings for interrupts. This size should be enough,
> >  	 * and I'm too lazy to allocate each name separately. */
> >  	char (*msix_names)[256];
> > +	char config_msix_name[256];
> >  	/* Number of available vectors */
> >  	unsigned msix_vectors;
> >  	/* Vectors allocated, excluding per-vq vectors if any */
> > @@ -282,12 +283,6 @@ static void vp_free_vectors(struct virtio_device
*vdev)
> >  			free_cpumask_var(vp_dev->msix_affinity_masks[i]);
> >  
> >  	if (vp_dev->msix_enabled) {
> > -		/* Disable the vector used for configuration */
> > -		iowrite16(VIRTIO_MSI_NO_VECTOR,
> > -			  vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> > -		/* Flush the write out to device */
> > -		ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> > -
> >  		pci_disable_msix(vp_dev->pci_dev);
> >  		vp_dev->msix_enabled = 0;
> >  	}
> > @@ -339,24 +334,18 @@ static int vp_request_msix_vectors(struct
virtio_device *vdev, int nvectors,
> >  		goto error;
> >  	vp_dev->msix_enabled = 1;
> >  
> > -	/* Set the vector used for configuration */
> > -	v = vp_dev->msix_used_vectors;
> > -	snprintf(vp_dev->msix_names[v], sizeof *vp_dev->msix_names,
> > +	/* Set shared IRQ for configuration */
> > +	snprintf(vp_dev->config_msix_name,
sizeof(*vp_dev->msix_names),
> >  		 "%s-config", name);
> > -	err = request_irq(vp_dev->msix_entries[v].vector,
> > -			  vp_config_changed, 0, vp_dev->msix_names[v],
> > +	err = request_irq(vp_dev->pci_dev->irq,
> > +			  vp_config_changed,
> > +			  IRQF_SHARED,
> > +			  vp_dev->config_msix_name,
> >  			  vp_dev);
> > -	if (err)
> > -		goto error;
> > -	++vp_dev->msix_used_vectors;
> > -
> > -	iowrite16(v, vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> > -	/* Verify we had enough resources to assign the vector */
> > -	v = ioread16(vp_dev->ioaddr + VIRTIO_MSI_CONFIG_VECTOR);
> > -	if (v == VIRTIO_MSI_NO_VECTOR) {
> > -		err = -EBUSY;
> > +	if (!err)
> > +		vp_dev->intx_enabled = 1;
> > +	else
> >  		goto error;
> > -	}
> >  
> >  	if (!per_vq_vectors) {
> >  		/* Shared vector for all VQs */
> > @@ -535,14 +524,16 @@ static int vp_try_to_find_vqs(struct
virtio_device *vdev, unsigned nvqs,
> >  			goto error_request;
> >  	} else {
> >  		if (per_vq_vectors) {
> > -			/* Best option: one for change interrupt, one per vq. */
> > -			nvectors = 1;
> > +			/* Best option: one normal interrupt for change,
> > +			   one msix per vq. */
> > +			nvectors = 0;
> >  			for (i = 0; i < nvqs; ++i)
> >  				if (callbacks[i])
> >  					++nvectors;
> >  		} else {
> > -			/* Second best: one for change, shared for all vqs. */
> > -			nvectors = 2;
> > +			/* Second best: one normal interrupt for
> > +			   change, share one msix for all vqs. */
> > +			nvectors = 1;
> >  		}
> >  
> >  		err = vp_request_msix_vectors(vdev, nvectors, per_vq_vectors);
> > -- 
> > 1.9.3
> --
> To unsubscribe from this list: send the line "unsubscribe kvm" in
> the body of a message to majordomo at vger.kernel.org
> More majordomo info at  http://vger.kernel.org/majordomo-info.html
-- 
			Amos.

Stefan Fritsch

2014-Sep-18 19:18 UTC

head link

[PATCH RFC] virtio-pci: share config interrupt between virtio devices

On Monday 01 September 2014 09:37:30, Michael S. Tsirkin
wrote:> Why do we need INT#x?
> How about setting IRQF_SHARED for the config interrupt
> while using MSI-X? You'd have to read ISR to check that the
> interrupt was intended for your device.
The virtio 0.9.5 spec says that ISR is "unused" when in MSI-X mode. I 
don't think that you can depend on the device to set the configuration 
changed bit.

The virtio 1.0 spec seems to have fixed that.

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