Re: [RFC net-next 0/7] Provide an ism layer

Dust Li
2025-02-10T05:09:00Z

On 2025-01-28 17:04:53, Alexandra Winter wrote:
>
>
>On 18.01.25 16:31, Dust Li wrote:
>> On 2025-01-17 11:38:39, Niklas Schnelle wrote:
>>> On Fri, 2025-01-17 at 10:13 +0800, Dust Li wrote:
>>>>>
>>> ---8<---
>>>>> Here are some of my thoughts on the matter:
>>>>>>>
>>>>>>> Naming and Structure: I suggest we refer to it as SHD (Shared Memory
>>>>>>> Device) instead of ISM (Internal Shared Memory).
>>>>>
>>>>>
>>>>> So where does the 'H' come from? If you want to call it Shared Memory _D_evice?
>>>>
>>>> Oh, I was trying to refer to SHM(Share memory file in the userspace, see man
>>>> shm_open(3)). SMD is also OK.
>>>>
>>>>>
>>>>>
>>>>> To my knowledge, a
>>>>>>> "Shared Memory Device" better encapsulates the functionality we're
>>>>>>> aiming to implement.
>>>>>
>>>>>
>>>>> Could you explain why that would be better?
>>>>> 'Internal Shared Memory' is supposed to be a bit of a counterpart to the
>>>>> Remote 'R' in RoCE. Not the greatest name, but it is used already by our ISM
>>>>> devices and by ism_loopback. So what is the benefit in changing it?
>>>>
>>>> I believe that if we are going to separate and refine the code, and add
>>>> a common subsystem, we should choose the most appropriate name.
>>>>
>>>> In my opinion, "ISM" doesn’t quite capture what the device provides.
>>>> Since we’re adding a "Device" that enables different entities (such as
>>>> processes or VMs) to perform shared memory communication, I think a more
>>>> fitting name would be better. If you have any alternative suggestions,
>>>> I’m open to them.
>>>
>>> I kept thinking about this a bit and I'd like to propose yet another
>>> name for this group of devices: Memory Communication Devices (MCD)
>>>
>>> One important point I see is that there is a bit of a misnomer in the
>>> existing ISM name in that our ISM device does in fact *not* share
>>> memory in the common sense of the "shared memory" wording. Instead it
>>> copies data between partitions of memory that share a common
>>> cache/memory hierarchy while not sharing the memory itself. loopback-
>>> ism and a possibly future virtio-ism on the other hand would share
>>> memory in the "shared memory" sense. Though I'd very much hope they
>>> will retain a copy mode to allow use in partition scenarios.
>>>
>>> With that background I think the common denominator between them and
>>> the main idea behind ISM is that they facilitate communication via
>>> memory buffers and very simple and reliable copy/share operations. I
>>> think this would also capture our planned use-case of devices (TTYs,
>>> block devices, framebuffers + HID etc) provided by a peer on top of
>>> such a memory communication device.
>>
>> Make sense, I agree with MCD.
>>
>> Best regard,
>> Dust
>>
>
>

Hi Winter,

Sorry for the late reply; we were on break for the Chinese Spring
Festival.

>
>In the discussion with Andrew Lunn, it showed that
>a) we need an abstract description of 'ISM' devices (noted)
>b) DMBs (Direct Memory Buffers) are a critical differentiator.
>
>So what do your think of Direct Memory Communication (DMC) as class name for these devices?
>
>I don't have a strong preference (we could also stay with ISM). But DMC may be a bit more
>concrete than MCD or ISM.

I personally prefer MCD over Direct Memory Communication (DMC).

For loopback or Virtio-ISM, DMC seems like a good choice. However, for
IBM ISM, since there's a DMA copy involved, it doesn’t seem truly "Direct,"
does it?

Additionally, since we are providing a device, MCD feels like a more
fitting choice, as it aligns better with the concept of a "device."

Best regards,
Dust