Re: [libvirt] [PATCH 0/5] Introduce NVDIMM support
On Mon, Aug 1, 2016 at 4:10 PM, Michal Privoznik <mprivozn(a)redhat.com> wrote:
NVDIMM was introduced to qemu in v2.6.0-rc0~248^2~25. So it's
been a while since then.
It's not the next big thing, but it is very interesting feature
enabling higher performance as reading/writing to the module (and
subsequently to the file on the host) does not require a VMEXIT.
It can be used to access host files directly bypassing page cache
whilst doing so.
How to test the feature?
1) you need PMEM enabled kernel:
CONFIG_LIBNVDIMM=y
CONFIG_BLK_DEV_PMEM=m
CONFIG_ACPI_NFIT=m
2) Create a file in the host:
truncate -s 512M /tmp/nvdimm
3) Add the following to the domain XML:
<memory model='nvdimm' memAccess='shared'>
<source>
<path>/tmp/nvdimm</path>
</source>
<target>
<size unit='KiB'>523264</size>
<node>0</node>
</target>
</memory>
The "nvdimm" device also has a label-size property. This determines
the size of the Namespace Label area described in:
http://pmem.io/documents/NVDIMM_Namespace_Spec.pdf
By default no Namespace Label area is reserved in the file. If the
user specifies label-size then the memory at the end of the file is
used as the Namespace Label area.
It is necessary to expose label-size so users can choose whether or
not to have a Namespace Label area.
I have CCed Guangrong Xiao who authored the QEMU patches.
Stefan