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qemu-e2k/docs/system/devices/virtio-pmem.rst

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virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
===========
virtio pmem
===========
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
This document explains the setup and usage of the virtio pmem device.
The virtio pmem device is a paravirtualized persistent memory device
on regular (i.e non-NVDIMM) storage.
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
Usecase
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
-------
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
Virtio pmem allows to bypass the guest page cache and directly use
host page cache. This reduces guest memory footprint as the host can
make efficient memory reclaim decisions under memory pressure.
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
How does virtio-pmem compare to the nvdimm emulation?
-----------------------------------------------------
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
NVDIMM emulation on regular (i.e. non-NVDIMM) host storage does not
persist the guest writes as there are no defined semantics in the device
specification. The virtio pmem device provides guest write persistence
on non-NVDIMM host storage.
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
virtio pmem usage
-----------------
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
A virtio pmem device backed by a memory-backend-file can be created on
the QEMU command line as in the following example::
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs: fix rst syntax errors in unbuilt docs The .rst files outside docs/{devel,interop,specs} aren't built yet and therefore a few syntax errors have slipped through. Fix them. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Message-Id: <20191111094411.427174-1-stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-11-11 10:44:11 +01:00
-object memory-backend-file,id=mem1,share,mem-path=./virtio_pmem.img,size=4G
-device virtio-pmem-pci,memdev=mem1,id=nv1
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
where:
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs: fix rst syntax errors in unbuilt docs The .rst files outside docs/{devel,interop,specs} aren't built yet and therefore a few syntax errors have slipped through. Fix them. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Message-Id: <20191111094411.427174-1-stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-11-11 10:44:11 +01:00
- "object memory-backend-file,id=mem1,share,mem-path=<image>, size=<image size>"
creates a backend file with the specified size.
- "device virtio-pmem-pci,id=nvdimm1,memdev=mem1" creates a virtio pmem
pci device whose storage is provided by above memory backend device.
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
Multiple virtio pmem devices can be created if multiple pairs of "-object"
and "-device" are provided.
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
Hotplug
-------
Virtio pmem devices can be hotplugged via the QEMU monitor. First, the
memory backing has to be added via 'object_add'; afterwards, the virtio
pmem device can be added via 'device_add'.
For example, the following commands add another 4GB virtio pmem device to
docs: fix rst syntax errors in unbuilt docs The .rst files outside docs/{devel,interop,specs} aren't built yet and therefore a few syntax errors have slipped through. Fix them. Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com> Reviewed-by: Daniel P. Berrangé <berrange@redhat.com> Message-Id: <20191111094411.427174-1-stefanha@redhat.com> Signed-off-by: Stefan Hajnoczi <stefanha@redhat.com>
2019-11-11 10:44:11 +01:00
the guest::
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
(qemu) object_add memory-backend-file,id=mem2,share=on,mem-path=virtio_pmem2.img,size=4G
(qemu) device_add virtio-pmem-pci,id=virtio_pmem2,memdev=mem2
Guest Data Persistence
----------------------
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
Guest data persistence on non-NVDIMM requires guest userspace applications
to perform fsync/msync. This is different from a real nvdimm backend where
no additional fsync/msync is required. This is to persist guest writes in
host backing file which otherwise remains in host page cache and there is
risk of losing the data in case of power failure.
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
With virtio pmem device, MAP_SYNC mmap flag is not supported. This provides
a hint to application to perform fsync for write persistence.
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
Limitations
docs/system/virtio-pmem.rst: Fix minor style issues The virtio-pmem documentation has some minor style issues we hadn't noticed since we weren't rendering it in our docs: * Sphinx doesn't complain about overlong title-underlining the way it complains about too-short underlining, but it looks odd; make the underlines of section headers the right length * Indent of paragraphs makes them render as blockquotes; remove the indent so they just render as normal text * Leading 'o' isn't rst markup, so it just renders as a literal "o"; reformat as a subsection heading instead * "QEMU" in the document title and section headings are a bit odd and unnecessary since this is the QEMU manual; delete or rephrase them * There's no need to specify what QEMU version the device first appeared in. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Reviewed-by: Alex Bennée <alex.bennee@linaro.org> Reviewed-by: Pankaj Gupta <pankaj.gupta@cloud.ionos.com>
2020-11-12 15:40:36 +01:00
-----------
virtio pmem: user document This patch documents the steps to use virtio pmem. It also documents other useful information about virtio pmem e.g use-case, comparison with Qemu NVDIMM backend and current limitations. Signed-off-by: Pankaj Gupta <pagupta@redhat.com> Message-Id: <20190821121624.5382-1-pagupta@redhat.com> Reviewed-by: Cornelia Huck <cohuck@redhat.com> Reviewed-by: Michael S. Tsirkin <mst@redhat.com> Signed-off-by: Michael S. Tsirkin <mst@redhat.com>
2019-08-21 14:16:24 +02:00
- Real nvdimm device backend is not supported.
- virtio pmem hotunplug is not supported.
- ACPI NVDIMM features like regions/namespaces are not supported.
- ndctl command is not supported.
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