Public bug reported:
This change provides a mechanism to reduce the number of MMIO doorbell writes
for the NVMe driver. When running in a virtualized environment like QEMU, the
cost of an MMIO is quite hefy here. The main idea for the patch is provide the
device two memory location locations:
1) to store the doorbell values so they can be lookup without the doorbell
MMIO write
2) to store an event index.
I believe the doorbell value is obvious, the event index not so much. Similar
to the virtio specificaiton, the virtual device can tell the driver (guest OS)
not to write MMIO unless you are writing past this value.
FYI: doorbell values are written by the nvme driver (guest OS) and the event
index is written by the virtual device (host OS).
The patch implements a new admin command that will communicate where these two
memory locations reside. If the command fails, the nvme driver will work as
before without any optimizations.
** Affects: linux (Ubuntu)
Importance: Undecided
Assignee: Tim Gardner (timg-tpi)
Status: In Progress
** Affects: linux (Ubuntu Xenial)
Importance: Undecided
Assignee: Tim Gardner (timg-tpi)
Status: In Progress
** Affects: linux (Ubuntu Yakkety)
Importance: Undecided
Assignee: Tim Gardner (timg-tpi)
Status: In Progress
** Affects: linux (Ubuntu Zesty)
Importance: Undecided
Assignee: Tim Gardner (timg-tpi)
Status: In Progress
** Also affects: linux (Ubuntu Zesty)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Yakkety)
Importance: Undecided
Status: New
** Also affects: linux (Ubuntu Xenial)
Importance: Undecided
Status: New
** Changed in: linux (Ubuntu Xenial)
Status: New => In Progress
** Changed in: linux (Ubuntu Xenial)
Assignee: (unassigned) => Tim Gardner (timg-tpi)
** Changed in: linux (Ubuntu Yakkety)
Status: New => In Progress
** Changed in: linux (Ubuntu Yakkety)
Assignee: (unassigned) => Tim Gardner (timg-tpi)
** Changed in: linux (Ubuntu Zesty)
Status: New => In Progress
** Changed in: linux (Ubuntu Zesty)
Assignee: (unassigned) => Tim Gardner (timg-tpi)
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https://bugs.launchpad.net/bugs/1637565
Title:
nvme: improve performance for virtual Google NVMe devices
Status in linux package in Ubuntu:
In Progress
Status in linux source package in Xenial:
In Progress
Status in linux source package in Yakkety:
In Progress
Status in linux source package in Zesty:
In Progress
Bug description:
This change provides a mechanism to reduce the number of MMIO doorbell writes
for the NVMe driver. When running in a virtualized environment like QEMU, the
cost of an MMIO is quite hefy here. The main idea for the patch is provide the
device two memory location locations:
1) to store the doorbell values so they can be lookup without the
doorbell
MMIO write
2) to store an event index.
I believe the doorbell value is obvious, the event index not so much. Similar
to the virtio specificaiton, the virtual device can tell the driver (guest OS)
not to write MMIO unless you are writing past this value.
FYI: doorbell values are written by the nvme driver (guest OS) and the event
index is written by the virtual device (host OS).
The patch implements a new admin command that will communicate where these
two memory locations reside. If the command fails, the nvme driver will work as
before without any optimizations.
To manage notifications about this bug go to:
https://bugs.launchpad.net/ubuntu/+source/linux/+bug/1637565/+subscriptions
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