Feng Liu
2023-May-16 13:54 UTC
[PATCH v1] virtio_pci: Optimize virtio_pci_device structure size
Improve the size of the virtio_pci_device structure, which is commonly
used to represent a virtio PCI device. A given virtio PCI device can
either of legacy type or modern type, with the
struct virtio_pci_legacy_device occupying 32 bytes and the
struct virtio_pci_modern_device occupying 88 bytes. Make them a union,
thereby save 32 bytes of memory as shown by the pahole tool. This
improvement is particularly beneficial when dealing with numerous
devices, as it helps conserve memory resources.
Before the modification, pahole tool reported the following:
struct virtio_pci_device {
[...]
struct virtio_pci_legacy_device ldev; /* 824 32 */
/* --- cacheline 13 boundary (832 bytes) was 24 bytes ago --- */
struct virtio_pci_modern_device mdev; /* 856 88 */
/* XXX last struct has 4 bytes of padding */
[...]
/* size: 1056, cachelines: 17, members: 19 */
[...]
};
After the modification, pahole tool reported the following:
struct virtio_pci_device {
[...]
union {
struct virtio_pci_legacy_device ldev; /* 824 32 */
struct virtio_pci_modern_device mdev; /* 824 88 */
}; /* 824 88 */
[...]
/* size: 1024, cachelines: 16, members: 18 */
[...]
};
Signed-off-by: Feng Liu <feliu at nvidia.com>
Reviewed-by: Jiri Pirko <jiri at nvidia.com>
---
drivers/virtio/virtio_pci_common.h | 7 ++++---
1 file changed, 4 insertions(+), 3 deletions(-)
diff --git a/drivers/virtio/virtio_pci_common.h
b/drivers/virtio/virtio_pci_common.h
index 23112d84218f..4b773bd7c58c 100644
--- a/drivers/virtio/virtio_pci_common.h
+++ b/drivers/virtio/virtio_pci_common.h
@@ -45,9 +45,10 @@ struct virtio_pci_vq_info {
struct virtio_pci_device {
struct virtio_device vdev;
struct pci_dev *pci_dev;
- struct virtio_pci_legacy_device ldev;
- struct virtio_pci_modern_device mdev;
-
+ union {
+ struct virtio_pci_legacy_device ldev;
+ struct virtio_pci_modern_device mdev;
+ };
bool is_legacy;
/* Where to read and clear interrupt */
--
2.37.1 (Apple Git-137.1)
Xuan Zhuo
2023-May-17 01:32 UTC
[PATCH v1] virtio_pci: Optimize virtio_pci_device structure size
On Tue, 16 May 2023 09:54:46 -0400, Feng Liu <feliu at nvidia.com> wrote:> Improve the size of the virtio_pci_device structure, which is commonly > used to represent a virtio PCI device. A given virtio PCI device can > either of legacy type or modern type, with the > struct virtio_pci_legacy_device occupying 32 bytes and the > struct virtio_pci_modern_device occupying 88 bytes. Make them a union, > thereby save 32 bytes of memory as shown by the pahole tool. This > improvement is particularly beneficial when dealing with numerous > devices, as it helps conserve memory resources. > > Before the modification, pahole tool reported the following: > struct virtio_pci_device { > [...] > struct virtio_pci_legacy_device ldev; /* 824 32 */ > /* --- cacheline 13 boundary (832 bytes) was 24 bytes ago --- */ > struct virtio_pci_modern_device mdev; /* 856 88 */ > > /* XXX last struct has 4 bytes of padding */ > [...] > /* size: 1056, cachelines: 17, members: 19 */ > [...] > }; > > After the modification, pahole tool reported the following: > struct virtio_pci_device { > [...] > union { > struct virtio_pci_legacy_device ldev; /* 824 32 */ > struct virtio_pci_modern_device mdev; /* 824 88 */ > }; /* 824 88 */ > [...] > /* size: 1024, cachelines: 16, members: 18 */ > [...] > }; > > Signed-off-by: Feng Liu <feliu at nvidia.com> > Reviewed-by: Jiri Pirko <jiri at nvidia.com>Reviewed-by: Xuan Zhuo <xuanzhuo at linux.alibaba.com> Thanks.> --- > drivers/virtio/virtio_pci_common.h | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h > index 23112d84218f..4b773bd7c58c 100644 > --- a/drivers/virtio/virtio_pci_common.h > +++ b/drivers/virtio/virtio_pci_common.h > @@ -45,9 +45,10 @@ struct virtio_pci_vq_info { > struct virtio_pci_device { > struct virtio_device vdev; > struct pci_dev *pci_dev; > - struct virtio_pci_legacy_device ldev; > - struct virtio_pci_modern_device mdev; > - > + union { > + struct virtio_pci_legacy_device ldev; > + struct virtio_pci_modern_device mdev; > + }; > bool is_legacy; > > /* Where to read and clear interrupt */ > -- > 2.37.1 (Apple Git-137.1) >
Jason Wang
2023-May-17 05:23 UTC
[PATCH v1] virtio_pci: Optimize virtio_pci_device structure size
On Tue, May 16, 2023 at 9:55?PM Feng Liu <feliu at nvidia.com> wrote:> > Improve the size of the virtio_pci_device structure, which is commonly > used to represent a virtio PCI device. A given virtio PCI device can > either of legacy type or modern type, with the > struct virtio_pci_legacy_device occupying 32 bytes and the > struct virtio_pci_modern_device occupying 88 bytes. Make them a union, > thereby save 32 bytes of memory as shown by the pahole tool. This > improvement is particularly beneficial when dealing with numerous > devices, as it helps conserve memory resources. > > Before the modification, pahole tool reported the following: > struct virtio_pci_device { > [...] > struct virtio_pci_legacy_device ldev; /* 824 32 */ > /* --- cacheline 13 boundary (832 bytes) was 24 bytes ago --- */ > struct virtio_pci_modern_device mdev; /* 856 88 */ > > /* XXX last struct has 4 bytes of padding */ > [...] > /* size: 1056, cachelines: 17, members: 19 */ > [...] > }; > > After the modification, pahole tool reported the following: > struct virtio_pci_device { > [...] > union { > struct virtio_pci_legacy_device ldev; /* 824 32 */ > struct virtio_pci_modern_device mdev; /* 824 88 */ > }; /* 824 88 */ > [...] > /* size: 1024, cachelines: 16, members: 18 */ > [...] > }; > > Signed-off-by: Feng Liu <feliu at nvidia.com> > Reviewed-by: Jiri Pirko <jiri at nvidia.com>Acked-by: Jason Wang <jasowang at redhat.com> Thanks> --- > drivers/virtio/virtio_pci_common.h | 7 ++++--- > 1 file changed, 4 insertions(+), 3 deletions(-) > > diff --git a/drivers/virtio/virtio_pci_common.h b/drivers/virtio/virtio_pci_common.h > index 23112d84218f..4b773bd7c58c 100644 > --- a/drivers/virtio/virtio_pci_common.h > +++ b/drivers/virtio/virtio_pci_common.h > @@ -45,9 +45,10 @@ struct virtio_pci_vq_info { > struct virtio_pci_device { > struct virtio_device vdev; > struct pci_dev *pci_dev; > - struct virtio_pci_legacy_device ldev; > - struct virtio_pci_modern_device mdev; > - > + union { > + struct virtio_pci_legacy_device ldev; > + struct virtio_pci_modern_device mdev; > + }; > bool is_legacy; > > /* Where to read and clear interrupt */ > -- > 2.37.1 (Apple Git-137.1) >