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From: "Aneesh Kumar K.V" <aneesh.kumar@linux.ibm.com>
To: David Gibson <david@gibson.dropbear.id.au>,
	Shivaprasad G Bhat <sbhat@linux.ibm.com>
Cc: sbhat@linux.vnet.ibm.com, groug@kaod.org, qemu-ppc@nongnu.org,
	ehabkost@redhat.com, marcel.apfelbaum@gmail.com, mst@redhat.com,
	imammedo@redhat.com, xiaoguangrong.eric@gmail.com,
	qemu-devel@nongnu.org, linux-nvdimm@lists.01.org,
	kvm-ppc@vger.kernel.org, shivaprasadbhat@gmail.com,
Subject: Re: [PATCH v3 2/3] spapr: nvdimm: Implement H_SCM_FLUSH hcall
Date: Wed, 24 Mar 2021 09:34:06 +0530	[thread overview]
Message-ID: <19b5aa0b-df85-256d-d4c4-eacd0ea8312e@linux.ibm.com> (raw)
In-Reply-To: <YFqs8M1dHAFhdCL6@yekko.fritz.box>

On 3/24/21 8:37 AM, David Gibson wrote:
> On Tue, Mar 23, 2021 at 09:47:38AM -0400, Shivaprasad G Bhat wrote:
>> The patch adds support for the SCM flush hcall for the nvdimm devices.
>> To be available for exploitation by guest through the next patch.
>> The hcall expects the semantics such that the flush to return
>> with H_BUSY when the operation is expected to take longer time along
>> with a continue_token. The hcall to be called again providing the
>> continue_token to get the status. So, all fresh requsts are put into
>> a 'pending' list and flush worker is submitted to the thread pool.
>> The thread pool completion callbacks move the requests to 'completed'
>> list, which are cleaned up after reporting to guest in subsequent
>> hcalls to get the status.
>> The semantics makes it necessary to preserve the continue_tokens
>> and their return status even across migrations. So, the pre_save
>> handler for the device waits for the flush worker to complete and
>> collects all the hcall states from 'completed' list. The necessary
>> nvdimm flush specific vmstate structures are added to the spapr
>> machine vmstate.
>> Signed-off-by: Shivaprasad G Bhat <sbhat@linux.ibm.com>
> An overal question: surely the same issue must arise on x86 with
> file-backed NVDIMMs.  How do they handle this case?

On x86 we have different ways nvdimm can be discovered. ACPI NFIT, e820 
map and virtio_pmem. Among these virio_pmem always operated with 
synchronous dax disabled and both ACPI and e820 doesn't have the ability 
to differentiate support for synchronous dax.

With that I would expect users to use virtio_pmem when using using file 
backed NVDIMMS

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  reply	other threads:[~2021-03-24  4:04 UTC|newest]

Thread overview: 13+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-03-23 13:47 [PATCH v3 0/3] spapr: nvdimm: Enable sync-dax property for nvdimm Shivaprasad G Bhat
2021-03-23 13:47 ` [PATCH v3 1/3] spapr: nvdimm: Forward declare and move the definitions Shivaprasad G Bhat
2021-03-24  2:30   ` David Gibson
2021-03-23 13:47 ` [PATCH v3 2/3] spapr: nvdimm: Implement H_SCM_FLUSH hcall Shivaprasad G Bhat
2021-03-24  3:07   ` David Gibson
2021-03-24  4:04     ` Aneesh Kumar K.V [this message]
2021-03-25  1:51       ` David Gibson
2021-03-26 13:45         ` Shivaprasad G Bhat
2021-03-29  9:23     ` Shivaprasad G Bhat
2021-03-30 23:57       ` David Gibson
2021-03-23 13:47 ` [PATCH v3 3/3] spapr: nvdimm: Enable sync-dax device property for nvdimm Shivaprasad G Bhat
2021-03-24  3:09   ` David Gibson
2021-03-24  4:09     ` Aneesh Kumar K.V

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