Re: [RFC 4/8] virtio-pci: Batch add/del ioeventfds in a single MR transaction

[Greg Kurz]

On Mon, 29 Mar 2021 18:24:40 +0100
Stefan Hajnoczi  wrote:

> On Thu, Mar 25, 2021 at 04:07:31PM +0100, Greg Kurz wrote:
> > diff --git a/softmmu/memory.c b/softmmu/memory.c
> > index 1b1942d521cc..0279e5671bcb 100644
> > --- a/softmmu/memory.c
> > +++ b/softmmu/memory.c
> > @@ -2368,7 +2368,7 @@ void memory_region_add_eventfd_full(MemoryRegion *mr,
> >  if (size) {
> >  adjust_endianness(mr, , size_memop(size) | MO_TE);
> >  }
> > -if (transaction) {
> > +if (!transaction) {
> >  memory_region_transaction_begin();
> >  }
> >  for (i = 0; i < mr->ioeventfd_nb; ++i) {
> > @@ -2383,7 +2383,7 @@ void memory_region_add_eventfd_full(MemoryRegion *mr,
> >  sizeof(*mr->ioeventfds) * (mr->ioeventfd_nb-1 - i));
> >  mr->ioeventfds[i] = mrfd;
> >  ioeventfd_update_pending |= mr->enabled;
> > -if (transaction) {
> > +if (!transaction) {
> >  memory_region_transaction_commit();
> >  }
> 
> Looks like these two hunks belong in a previous patch.

And they are actually wrong... we *do* want a nested
transaction if 'transaction' is true :) This is a
leftover I thought I had removed but obviously not...


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Re: [RFC 4/8] virtio-pci: Batch add/del ioeventfds in a single MR transaction

[Stefan Hajnoczi]

On Thu, Mar 25, 2021 at 04:07:31PM +0100, Greg Kurz wrote:
> diff --git a/softmmu/memory.c b/softmmu/memory.c
> index 1b1942d521cc..0279e5671bcb 100644
> --- a/softmmu/memory.c
> +++ b/softmmu/memory.c
> @@ -2368,7 +2368,7 @@ void memory_region_add_eventfd_full(MemoryRegion *mr,
>  if (size) {
>  adjust_endianness(mr, , size_memop(size) | MO_TE);
>  }
> -if (transaction) {
> +if (!transaction) {
>  memory_region_transaction_begin();
>  }
>  for (i = 0; i < mr->ioeventfd_nb; ++i) {
> @@ -2383,7 +2383,7 @@ void memory_region_add_eventfd_full(MemoryRegion *mr,
>  sizeof(*mr->ioeventfds) * (mr->ioeventfd_nb-1 - i));
>  mr->ioeventfds[i] = mrfd;
>  ioeventfd_update_pending |= mr->enabled;
> -if (transaction) {
> +if (!transaction) {
>  memory_region_transaction_commit();
>  }

Looks like these two hunks belong in a previous patch.


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[RFC 4/8] virtio-pci: Batch add/del ioeventfds in a single MR transaction

[Greg Kurz]

Implement the ioeventfd_assign_begin() and ioeventfd_assign_commit()
handlers of VirtioBusClass. Basically track that a transaction was
already requested by the device and use this information to prevent
the memory code to generate a transaction for each individual eventfd.

Devices that want to benefit of this batching feature must be converted
to use the virtio_bus_set_host_notifiers() API.

Signed-off-by: Greg Kurz 
---
 hw/virtio/virtio-pci.h |  1 +
 hw/virtio/virtio-pci.c | 53 +-
 softmmu/memory.c   |  4 ++--
 3 files changed, 40 insertions(+), 18 deletions(-)

diff --git a/hw/virtio/virtio-pci.h b/hw/virtio/virtio-pci.h
index d7d5d403a948..a1b3f1bc45c9 100644
--- a/hw/virtio/virtio-pci.h
+++ b/hw/virtio/virtio-pci.h
@@ -141,6 +141,7 @@ struct VirtIOPCIProxy {
 bool disable_modern;
 bool ignore_backend_features;
 OnOffAuto disable_legacy;
+bool ioeventfd_assign_started;
 uint32_t class_code;
 uint32_t nvectors;
 uint32_t dfselect;
diff --git a/hw/virtio/virtio-pci.c b/hw/virtio/virtio-pci.c
index 883045a22354..0a8738c69541 100644
--- a/hw/virtio/virtio-pci.c
+++ b/hw/virtio/virtio-pci.c
@@ -243,47 +243,66 @@ static int virtio_pci_ioeventfd_assign(DeviceState *d, 
EventNotifier *notifier,
 hwaddr modern_addr = virtio_pci_queue_mem_mult(proxy) *
  virtio_get_queue_index(vq);
 hwaddr legacy_addr = VIRTIO_PCI_QUEUE_NOTIFY;
+bool transaction = !proxy->ioeventfd_assign_started;
 
 if (assign) {
 if (modern) {
 if (fast_mmio) {
-memory_region_add_eventfd(modern_mr, modern_addr, 0,
-  false, n, notifier);
+memory_region_add_eventfd_full(modern_mr, modern_addr, 0,
+   false, n, notifier, 
transaction);
 } else {
-memory_region_add_eventfd(modern_mr, modern_addr, 2,
-  false, n, notifier);
+memory_region_add_eventfd_full(modern_mr, modern_addr, 2,
+   false, n, notifier, 
transaction);
 }
 if (modern_pio) {
-memory_region_add_eventfd(modern_notify_mr, 0, 2,
-  true, n, notifier);
+memory_region_add_eventfd_full(modern_notify_mr, 0, 2,
+   true, n, notifier, transaction);
 }
 }
 if (legacy) {
-memory_region_add_eventfd(legacy_mr, legacy_addr, 2,
-  true, n, notifier);
+memory_region_add_eventfd_full(legacy_mr, legacy_addr, 2,
+   true, n, notifier, transaction);
 }
 } else {
 if (modern) {
 if (fast_mmio) {
-memory_region_del_eventfd(modern_mr, modern_addr, 0,
-  false, n, notifier);
+memory_region_del_eventfd_full(modern_mr, modern_addr, 0,
+   false, n, notifier, 
transaction);
 } else {
-memory_region_del_eventfd(modern_mr, modern_addr, 2,
-  false, n, notifier);
+memory_region_del_eventfd_full(modern_mr, modern_addr, 2,
+   false, n, notifier, 
transaction);
 }
 if (modern_pio) {
-memory_region_del_eventfd(modern_notify_mr, 0, 2,
-  true, n, notifier);
+memory_region_del_eventfd_full(modern_notify_mr, 0, 2,
+   true, n, notifier, transaction);
 }
 }
 if (legacy) {
-memory_region_del_eventfd(legacy_mr, legacy_addr, 2,
-  true, n, notifier);
+memory_region_del_eventfd_full(legacy_mr, legacy_addr, 2,
+   true, n, notifier, transaction);
 }
 }
 return 0;
 }
 
+static void virtio_pci_ioeventfd_assign_begin(DeviceState *d)
+{
+VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
+
+assert(!proxy->ioeventfd_assign_started);
+proxy->ioeventfd_assign_started = true;
+memory_region_transaction_begin();
+}
+
+static void virtio_pci_ioeventfd_assign_commit(DeviceState *d)
+{
+VirtIOPCIProxy *proxy = to_virtio_pci_proxy(d);
+
+assert(proxy->ioeventfd_assign_started);
+memory_region_transaction_commit();
+proxy->ioeventfd_assign_started = false;
+}
+
 static void virtio_pci_start_ioeventfd(VirtIOPCIProxy *proxy)
 {
 virtio_bus_start_ioeventfd(>bus);
@@ -2161,6 +2180,8 @@ static void virtio_pci_bus_class_init(ObjectClass *klass, 
void *data)
 k->query_nvectors = virtio_pci_query_nvectors;