From: "Cédric Le Goater" <clg@kaod.org>
To: Shivaprasad G Bhat <sbhat@linux.ibm.com>,
mst@redhat.com, ani@anisinha.ca, danielhb413@gmail.com,
david@gibson.dropbear.id.au, groug@kaod.org, imammedo@redhat.com,
xiaoguangrong.eric@gmail.com, qemu-ppc@nongnu.org
Cc: aneesh.kumar@linux.ibm.com, qemu-devel@nongnu.org,
kvm-ppc@vger.kernel.org, nvdimm@lists.linux.dev
Subject: Re: [PATCH v7 0/3] spapr: nvdimm: Introduce spapr-nvdimm device
Date: Fri, 18 Feb 2022 07:44:02 +0000 [thread overview]
Message-ID: <66c4c578-d8ac-8a2c-91d0-9c6b26ed39eb@kaod.org> (raw)
In-Reply-To: <164396252398.109112.13436924292537517470.stgit@ltczzess4.aus.stglabs.ibm.com>
On 2/4/22 09:15, Shivaprasad G Bhat wrote:
> If the device backend is not persistent memory for the nvdimm, there
> is need for explicit IO flushes to ensure persistence.
>
> On SPAPR, the issue is addressed by adding a new hcall to request for
> an explicit flush from the guest when the backend is not pmem.
> So, the approach here is to convey when the hcall flush is required
> in a device tree property. The guest once it knows the device needs
> explicit flushes, makes the hcall as and when required.
>
> It was suggested to create a new device type to address the
> explicit flush for such backends on PPC instead of extending the
> generic nvdimm device with new property. So, the patch introduces
> the spapr-nvdimm device. The new device inherits the nvdimm device
> with the new bahviour such that if the backend has pmem=no, the
> device tree property is set by default.
>
> The below demonstration shows the map_sync behavior for non-pmem
> backends.
> (https://github.com/avocado-framework-tests/avocado-misc-tests/blob/master/memory/ndctl.py.data/map_sync.c)
>
> The pmem0 is from spapr-nvdimm with with backend pmem=on, and pmem1 is
> from spapr-nvdimm with pmem=off, mounted as
> /dev/pmem0 on /mnt1 type xfs (rw,relatime,attr2,dax=always,inode64,logbufs=8,logbsize2k,noquota)
> /dev/pmem1 on /mnt2 type xfs (rw,relatime,attr2,dax=always,inode64,logbufs=8,logbsize2k,noquota)
>
> [root@atest-guest ~]# ./mapsync /mnt1/newfile ----> When pmem=on
> [root@atest-guest ~]# ./mapsync /mnt2/newfile ----> when pmem=off
> Failed to mmap with Operation not supported
>
> First patch adds the realize/unrealize call backs to the generic device
> for the new device's vmstate registration. The second patch implements
> the hcall, adds the necessary vmstate properties to spapr machine structure
> for carrying the hcall status during save-restore. The nature of the hcall
> being asynchronus, the patch uses aio utilities to offload the flush. The
> third patch introduces the spapr-nvdimm device, adds the device tree
> property for the guest when spapr-nvdimm is used with pmem=no on the
> backend. Also adds new property pmem-override(?, suggest if you have better
> name) to the spapr-nvdimm which hints at forcing the hcall based flushes even
> on pmem backed devices.
>
> The kernel changes to exploit this hcall is at
> https://github.com/linuxppc/linux/commit/75b7c05ebf9026.patch
Applied for ppc-7.0
Thanks,
C.
prev parent reply other threads:[~2022-02-18 7:44 UTC|newest]
Thread overview: 7+ messages / expand[flat|nested] mbox.gz Atom feed top
2022-02-04 8:15 [PATCH v7 0/3] spapr: nvdimm: Introduce spapr-nvdimm device Shivaprasad G Bhat
2022-02-04 8:15 ` [PATCH v7 1/3] nvdimm: Add realize, unrealize callbacks to NVDIMMDevice class Shivaprasad G Bhat
2022-02-04 8:15 ` [PATCH v7 2/3] spapr: nvdimm: Implement H_SCM_FLUSH hcall Shivaprasad G Bhat
2022-02-07 11:48 ` Daniel Henrique Barboza
2022-02-04 8:16 ` [PATCH v7 3/3] spapr: nvdimm: Introduce spapr-nvdimm device Shivaprasad G Bhat
2022-02-07 11:53 ` [PATCH v7 0/3] " Daniel Henrique Barboza
2022-02-18 7:44 ` Cédric Le Goater [this message]
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