Re: [PATCH v4 0/3] nvdimm: Enable sync-dax property for nvdimm

[Stefan Hajnoczi <stefanha@redhat.com>]

[-- Attachment #1.1: Type: text/plain, Size: 1247 bytes --]

On Wed, Apr 28, 2021 at 11:48:21PM -0400, Shivaprasad G Bhat wrote:
> The nvdimm devices are expected to ensure write persistence during power
> failure kind of scenarios.
> 
> The libpmem has architecture specific instructions like dcbf on POWER
> to flush the cache data to backend nvdimm device during normal writes
> followed by explicit flushes if the backend devices are not synchronous
> DAX capable.
> 
> Qemu - virtual nvdimm devices are memory mapped. The dcbf in the guest
> and the subsequent flush doesn't traslate to actual flush to the backend
> file on the host in case of file backed v-nvdimms. This is addressed by
> virtio-pmem in case of x86_64 by making explicit flushes translating to
> fsync at qemu.
> 
> On SPAPR, the issue is addressed by adding a new hcall to
> request for an explicit flush from the guest ndctl driver when the backend
> nvdimm cannot ensure write persistence with dcbf alone. So, the approach
> here is to convey when the hcall flush is required in a device tree
> property. The guest makes the hcall when the property is found, instead
> of relying on dcbf.

Sorry, I'm not very familiar with SPAPR. Why add a hypercall when the
virtio-nvdimm device already exists?

Stefan

[-- Attachment #1.2: signature.asc --]
[-- Type: application/pgp-signature, Size: 488 bytes --]

[-- Attachment #2: Type: text/plain, Size: 167 bytes --]

_______________________________________________
Linux-nvdimm mailing list -- linux-nvdimm@lists.01.org
To unsubscribe send an email to linux-nvdimm-leave@lists.01.org