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4f0fc22534
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@nvidia.com>
Reviewed-by: Jiri Pirko <jiri@nvidia.com>
Message-Id: <20230516135446.16266-1-feliu@nvidia.com>
Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
Reviewed-by: Xuan Zhuo <xuanzhuo@linux.alibaba.com>
Acked-by: Jason Wang <jasowang@redhat.com>
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Linux kernel
============
There are several guides for kernel developers and users. These guides can
be rendered in a number of formats, like HTML and PDF. Please read
Documentation/admin-guide/README.rst first.
In order to build the documentation, use ``make htmldocs`` or
``make pdfdocs``. The formatted documentation can also be read online at:
https://www.kernel.org/doc/html/latest/
There are various text files in the Documentation/ subdirectory,
several of them using the Restructured Text markup notation.
Please read the Documentation/process/changes.rst file, as it contains the
requirements for building and running the kernel, and information about
the problems which may result by upgrading your kernel.