Re: [LSF/MM TOPIC] CAPI/CCIX cache coherent device memory (NUMA too ?)

From: "Liubo(OS Lab)" <liubo95@huawei.com>
To: Jerome Glisse <jglisse@redhat.com>, lsf-pc@lists.linux-foundation.org
Cc: linux-mm@kvack.org,
	Anshuman Khandual <khandual@linux.vnet.ibm.com>,
	Balbir Singh <bsingharora@gmail.com>,
	Dan Williams <dan.j.williams@intel.com>,
	John Hubbard <jhubbard@nvidia.com>,
	Jonathan Masters <jcm@redhat.com>,
	Ross Zwisler <ross.zwisler@linux.intel.com>
Subject: Re: [LSF/MM TOPIC] CAPI/CCIX cache coherent device memory (NUMA too ?)
Date: Wed, 17 Jan 2018 09:32:59 +0800	[thread overview]
Message-ID: <c02d666d-d985-990f-eeec-e3e677a1b046@huawei.com> (raw)
In-Reply-To: <20180116210321.GB8801@redhat.com>

On 2018/1/17 5:03, Jerome Glisse wrote:
> CAPI (on IBM Power8 and 9) and CCIX are two new standard that
> build on top of existing interconnect (like PCIE) and add the
> possibility for cache coherent access both way (from CPU to
> device memory and from device to main memory). This extend
> what we are use to with PCIE (where only device to main memory
> can be cache coherent but not CPU to device memory).
> 

Yes, and more than CAPI/CCIX.
E.g A SoC may connected with different types of memory through internal system-bus.

> How is this memory gonna be expose to the kernel and how the
> kernel gonna expose this to user space is the topic i want to
> discuss. I believe this is highly device specific for instance
> for GPU you want the device memory allocation and usage to be
> under the control of the GPU device driver. Maybe other type
> of device want different strategy.
> 
> The HMAT patchset is partialy related to all this as it is about
> exposing different type of memory available in a system for CPU
> (HBM, main memory, ...) and some of their properties (bandwidth,
> latency, ...).
> 

Yes, and different type of memory doesn't mean device-memory or Nvdimm only(which are always think not as reliable as DDR).

> 
> We can start by looking at how CAPI and CCIX plan to expose this
> to the kernel and try to list some of the type of devices we
> expect to see. Discussion can then happen on how to represent this
> internaly to the kernel and how to expose this to userspace.
> 
> Note this might also trigger discussion on a NUMA like model or
> on extending/replacing it by something more generic.
> 

Agree, for NUMA model the node distance is not enough when a system has different type of memory.
Like the HMAT patches mentioned, different bandwidth ,latency, ...

> 
> Peoples (alphabetical order on first name) sorry if i missed
> anyone:
>     "Anshuman Khandual" <khandual@linux.vnet.ibm.com>
>     "Balbir Singh" <bsingharora@gmail.com>
>     "Dan Williams" <dan.j.williams@intel.com>
>     "John Hubbard" <jhubbard@nvidia.com>
>     "Jonathan Masters" <jcm@redhat.com>
>     "Ross Zwisler" <ross.zwisler@linux.intel.com>
> 

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