Re: [libvirt] [PATCH 0/5] Introduce NVDIMM support

On 04.08.2016 10:42, Stefan Hajnoczi wrote: > On Mon, Aug 1, 2016 at 4:10 PM, Michal Privoznik <mprivozn(a)redhat.com&gt; 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. > Ah, thank you for that. From the code I understand that the minimum value for that is 128K, but what about other restrictions? Does the number need to be aligned? What is the minimal step between two different values?