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Re: [Qemu-devel] [PATCH] virtio-pci: reduce modern_mem_bar size
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From: |
Michael S. Tsirkin |
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Subject: |
Re: [Qemu-devel] [PATCH] virtio-pci: reduce modern_mem_bar size |
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Date: |
Wed, 7 Sep 2016 17:35:22 +0300 |
On Wed, Sep 07, 2016 at 04:53:09PM +0300, Marcel Apfelbaum wrote:
> Currently each VQ Notification Virtio Capability is allocated
> on a different page. The idea is to enable split drivers within
> guests, however there are no known plans to do that.
> The allocation will result in a 8MB BAR, more than various
> guest firmwares pre-allocates for PCI Bridges hotplug process.
>
> Reserve 4 bytes per VQ by default and add a new parameter
> "page-per-vq" to be used with split drivers.
>
> Signed-off-by: Marcel Apfelbaum <address@hidden>
> ---
> Hi,
>
> To be applied on top of:
> [PATCH v5 1/2] pc: Add 2.8 machine
> (http://patchwork.ozlabs.org/patch/666812/)
>
> Thanks,
> Marcel
>
> hw/virtio/virtio-pci.c | 18 +++++++++++-------
> hw/virtio/virtio-pci.h | 6 ++++++
> include/hw/compat.h | 6 +++++-
> 3 files changed, 22 insertions(+), 8 deletions(-)
>
> diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
> index 755f921..25e7ffa 100644
> --- a/hw/virtio/virtio-pci.c
> +++ b/hw/virtio/virtio-pci.c
> @@ -307,7 +307,7 @@ static int virtio_pci_ioeventfd_assign(DeviceState *d,
> EventNotifier *notifier,
> MemoryRegion *modern_mr = &proxy->notify.mr;
> MemoryRegion *modern_notify_mr = &proxy->notify_pio.mr;
> MemoryRegion *legacy_mr = &proxy->bar;
> - hwaddr modern_addr = QEMU_VIRTIO_PCI_QUEUE_MEM_MULT *
> + hwaddr modern_addr = proxy->queue_mem_mult *
> virtio_get_queue_index(vq);
> hwaddr legacy_addr = VIRTIO_PCI_QUEUE_NOTIFY;
>
> @@ -1370,7 +1370,8 @@ static void virtio_pci_notify_write(void *opaque,
> hwaddr addr,
> uint64_t val, unsigned size)
> {
> VirtIODevice *vdev = opaque;
> - unsigned queue = addr / QEMU_VIRTIO_PCI_QUEUE_MEM_MULT;
> + VirtIOPCIProxy *proxy = VIRTIO_PCI(DEVICE(vdev)->parent_bus->parent);
> + unsigned queue = addr / proxy->queue_mem_mult;
>
> if (queue < VIRTIO_QUEUE_MAX) {
> virtio_queue_notify(vdev, queue);
> @@ -1609,7 +1610,7 @@ static void virtio_pci_device_plugged(DeviceState *d,
> Error **errp)
> struct virtio_pci_notify_cap notify = {
> .cap.cap_len = sizeof notify,
> .notify_off_multiplier =
> - cpu_to_le32(QEMU_VIRTIO_PCI_QUEUE_MEM_MULT),
> + cpu_to_le32(proxy->queue_mem_mult),
> };
> struct virtio_pci_cfg_cap cfg = {
> .cap.cap_len = sizeof cfg,
> @@ -1717,6 +1718,9 @@ static void virtio_pci_realize(PCIDevice *pci_dev,
> Error **errp)
> bool pcie_port = pci_bus_is_express(pci_dev->bus) &&
> !pci_bus_is_root(pci_dev->bus);
>
> + proxy->queue_mem_mult = (proxy->flags & VIRTIO_PCI_FLAG_PAGE_PER_VQ) ?
> + QEMU_VIRTIO_PCI_QUEUE_MEM_MULT : 4;
> +
> /*
> * virtio pci bar layout used by default.
> * subclasses can re-arrange things if needed.
> @@ -1744,8 +1748,7 @@ static void virtio_pci_realize(PCIDevice *pci_dev,
> Error **errp)
> proxy->device.type = VIRTIO_PCI_CAP_DEVICE_CFG;
>
> proxy->notify.offset = 0x3000;
> - proxy->notify.size =
> - QEMU_VIRTIO_PCI_QUEUE_MEM_MULT * VIRTIO_QUEUE_MAX;
> + proxy->notify.size = proxy->queue_mem_mult * VIRTIO_QUEUE_MAX;
> proxy->notify.type = VIRTIO_PCI_CAP_NOTIFY_CFG;
>
> proxy->notify_pio.offset = 0x0;
> @@ -1754,8 +1757,7 @@ static void virtio_pci_realize(PCIDevice *pci_dev,
> Error **errp)
>
> /* subclasses can enforce modern, so do this unconditionally */
> memory_region_init(&proxy->modern_bar, OBJECT(proxy), "virtio-pci",
> - 2 * QEMU_VIRTIO_PCI_QUEUE_MEM_MULT *
> - VIRTIO_QUEUE_MAX);
Maybe add
/* PCI BAR regions must be powers of 2 */
> + pow2ceil(proxy->notify.offset + proxy->notify.size));
>
> memory_region_init_alias(&proxy->modern_cfg,
> OBJECT(proxy),
> @@ -1833,6 +1835,8 @@ static Property virtio_pci_properties[] = {
> VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY_BIT, false),
> DEFINE_PROP_BIT("x-disable-pcie", VirtIOPCIProxy, flags,
> VIRTIO_PCI_FLAG_DISABLE_PCIE_BIT, false),
> + DEFINE_PROP_BIT("page-per-vq", VirtIOPCIProxy, flags,
> + VIRTIO_PCI_FLAG_PAGE_PER_VQ_BIT, false),
> DEFINE_PROP_END_OF_LIST(),
> };
>
> diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
> index 25fbf8a..0fd0d37 100644
> --- a/hw/virtio/virtio-pci.h
> +++ b/hw/virtio/virtio-pci.h
> @@ -64,6 +64,7 @@ enum {
> VIRTIO_PCI_FLAG_MIGRATE_EXTRA_BIT,
> VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY_BIT,
> VIRTIO_PCI_FLAG_DISABLE_PCIE_BIT,
> + VIRTIO_PCI_FLAG_PAGE_PER_VQ_BIT,
> };
>
> /* Need to activate work-arounds for buggy guests at vmstate load. */
> @@ -84,6 +85,10 @@ enum {
> #define VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY \
> (1 << VIRTIO_PCI_FLAG_MODERN_PIO_NOTIFY_BIT)
>
> +/* page per vq flag to be used by split drivers within guests */
> +#define VIRTIO_PCI_FLAG_PAGE_PER_VQ \
> + (1 << VIRTIO_PCI_FLAG_PAGE_PER_VQ_BIT)
> +
> typedef struct {
> MSIMessage msg;
> int virq;
> @@ -138,6 +143,7 @@ struct VirtIOPCIProxy {
> uint32_t msix_bar;
> uint32_t modern_io_bar;
> uint32_t modern_mem_bar;
> + int queue_mem_mult;
> int config_cap;
> uint32_t flags;
> bool disable_modern;
I would rather use wrapper functions to calculate it,
to avoid duplicating data.
E.g.
static inline int virtio_pci_queue_mem_mult(struct VirtIOPCIProxy *)
{
return (proxy->flags & VIRTIO_PCI_FLAG_PAGE_PER_VQ) ?
QEMU_VIRTIO_PCI_QUEUE_MEM_MULT : 4;
}
Otherwise, looks fine.
> diff --git a/include/hw/compat.h b/include/hw/compat.h
> index 08dd4fb..a1d6694 100644
> --- a/include/hw/compat.h
> +++ b/include/hw/compat.h
> @@ -2,7 +2,11 @@
> #define HW_COMPAT_H
>
> #define HW_COMPAT_2_7 \
> - /* empty */
> + {\
> + .driver = "virtio-pci",\
> + .property = "page-per-vq",\
> + .value = "on",\
> + },
>
> #define HW_COMPAT_2_6 \
> {\
> --
> 2.5.5