2023-04-27 17:38:22

by Reinette Chatre

Subject: [PATCH V4 08/11] vfio/pci: Use bitfield for struct vfio_pci_core_device flags

struct vfio_pci_core_device contains eleven boolean flags.
Boolean flags clearly indicate their usage but space usage
starts to be a concern when there are many.

An upcoming change adds another boolean flag to
struct vfio_pci_core_device, thereby increasing the concern
that the boolean flags are consuming unnecessary space.

Transition the boolean flags to use bitfields. On a system that
uses one byte per boolean this reduces the space consumed
by existing flags from 11 bytes to 2 bytes with room for
a few more flags without increasing the structure's size.

Suggested-by: Jason Gunthorpe <[email protected]>
Signed-off-by: Reinette Chatre <[email protected]>
---
Changes since V3:
- New patch. (Jason)

include/linux/vfio_pci_core.h | 22 +++++++++++-----------
1 file changed, 11 insertions(+), 11 deletions(-)

diff --git a/include/linux/vfio_pci_core.h b/include/linux/vfio_pci_core.h
index 148fd1ae6c1c..adb47e2914d7 100644
--- a/include/linux/vfio_pci_core.h
+++ b/include/linux/vfio_pci_core.h
@@ -68,17 +68,17 @@ struct vfio_pci_core_device {
u16 msix_size;
u32 msix_offset;
u32 rbar[7];
- bool pci_2_3;
- bool virq_disabled;
- bool reset_works;
- bool extended_caps;
- bool bardirty;
- bool has_vga;
- bool needs_reset;
- bool nointx;
- bool needs_pm_restore;
- bool pm_intx_masked;
- bool pm_runtime_engaged;
+ bool pci_2_3:1;
+ bool virq_disabled:1;
+ bool reset_works:1;
+ bool extended_caps:1;
+ bool bardirty:1;
+ bool has_vga:1;
+ bool needs_reset:1;
+ bool nointx:1;
+ bool needs_pm_restore:1;
+ bool pm_intx_masked:1;
+ bool pm_runtime_engaged:1;
struct pci_saved_state *pci_saved_state;
struct pci_saved_state *pm_save;
int ioeventfds_nr;
--
2.34.1

2023-04-28 06:47:46

by Tian, Kevin

Subject: RE: [PATCH V4 08/11] vfio/pci: Use bitfield for struct vfio_pci_core_device flags

> From: Chatre, Reinette <[email protected]>
> Sent: Friday, April 28, 2023 1:36 AM
>
> struct vfio_pci_core_device contains eleven boolean flags.
> Boolean flags clearly indicate their usage but space usage
> starts to be a concern when there are many.
>
> An upcoming change adds another boolean flag to
> struct vfio_pci_core_device, thereby increasing the concern
> that the boolean flags are consuming unnecessary space.
>
> Transition the boolean flags to use bitfields. On a system that
> uses one byte per boolean this reduces the space consumed
> by existing flags from 11 bytes to 2 bytes with room for
> a few more flags without increasing the structure's size.
>
> Suggested-by: Jason Gunthorpe <[email protected]>
> Signed-off-by: Reinette Chatre <[email protected]>

Reviewed-by: Kevin Tian <[email protected]>