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Re: [Qemu-devel] Towards an ivshmem 2.0?

From: Måns Rullgård
Subject: Re: [Qemu-devel] Towards an ivshmem 2.0?
Date: Mon, 23 Jan 2017 10:14:53 +0000
User-agent: Gnus/5.13 (Gnus v5.13) Emacs/24.5 (gnu/linux)

"Wang, Wei W" <address@hidden> writes:

> On Saturday, January 21, 2017 12:38 AM, Jan Kiszka wrote:
>> On 2017-01-20 12:54, Wang, Wei W wrote:
>>> Having a theoretical analysis on the performance: The traditional
>>> shared memory mechanism, sharing an intermediate memory, requires 2
>>> copies to get the packet transmitted. It's not just one more copy
>>> compared to the 1-copy solution, I think some more things we may
>>> need to take into account:
>> 1-copy (+potential transfers to userspace, but that's the same for
>> everyone) is conceptually possible, definitely under stacks like
>> DPDK.  However, Linux skbs are currently not prepared for picking up
>> shmem-backed packets, we already looked into this. Likely
>> addressable, though.
> Not sure how difficult it would be to get that change upstream-ed to
> the kernel, but looking forward to seeing your solutions.

The problem is that the shared memory mapping doesn't have a struct page
as required by lots of networking code.

Måns Rullgård

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