[HN Gopher] The Demikernel Datapath OS Architecture for Microsec...
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The Demikernel Datapath OS Architecture for Microsecond-Scale
Datacenter Systems
Author : zdw
Score : 24 points
Date : 2021-11-16 04:54 UTC (18 hours ago)
(HTM) web link (www.micahlerner.com)
(TXT) w3m dump (www.micahlerner.com)
| deadgrey19 wrote:
| Yet another academic work in the OS space that should have been
| tested against the the state of the art in (commercially backed)
| networking space.
|
| From the abstract:
|
| > However, none of these systems offer a general-purpose datapath
| OS replacement that meet the needs of us-scale systems
|
| One of the key points that the authors use to motivate their work
| is that using kernel bypass technologies is hard because it
| requires software engineers to rearchitect their code.
|
| Call me sceptical of that claim. I can think of 3 (open source)
| systems that provide drop-in replacement network interfaces for
| existing software, but offer nanosecond (not microsecond!) scale
| performance.
|
| - Solarflare/Xilinx Open Onload - https://github.com/Xilinx-
| CNS/onload
|
| - Exablaze/Cisco - ExaSOCK - https://github.com/cisco/exanic-
| software
|
| - Melanox/NVidia VMA - https://github.com/Mellanox/libvma
|
| With each of the above systems, they are designed to offer low
| latency network stack replacement for existing applications,
| without code modification or even recompilation. Exactly the
| authors' goals.
|
| But there is not a single reference to any of these technologies
| in the paper. And crucially no comparison to any of them in the
| evaluation.
|
| The authors seem blissfully unaware of what work has actually
| been done to solve these problems. Which makes the contributions
| of the paper ... somewhat dubious.
| scrubs wrote:
| Note that Solarflare requires a per NIC license to get that by-
| pass. And like Melanox those NICs are not cheap. Kernel by-pass
| on COTS without recourse to high end NICs w/ or w/o FPGA and
| the like is needed. I am benchmarking eRPC built on top of DPDK
| on AWS to that end [1]. And not having to play sys-admin and
| figure out configs or at least simplifying that work would
| help. [1] https://www.usenix.org/system/files/nsdi19-kalia.pdf
| tobz wrote:
| One crucial difference I was able to spot is that Demikernel
| seems to have an approach that can work for OSes other than
| Linux. To wit, examples of the performance of the Demikernel
| approach are shown on a Windows system running in Azure.
|
| Of the three examples you listed, none of them seem to support
| their kernel bypass capabilities in anything other than Linux.
| deadgrey19 wrote:
| Fair enough. My guess is that the commercial solutions are
| simply going where the money is. If there was a commercially
| pressing need to port to other systems, I'm sure it can be
| done.
|
| With that said, it's one thing to have a legitimate reason
| for preferring an alternative approach. But the paper doesn't
| even mention these solutions, which means that the authors
| are either ignorant of what's already been done (bad), or
| deliberately avoiding comparisons to alternative approaches
| (worse).
| sujayakar wrote:
| hey, sujay (one of the authors from the paper) here! happy to
| answer any questions about the paper/system.
| eqvinox wrote:
| Well, not a question.
|
| POSIX and Linux are not the same. There is no epoll in POSIX,
| it's a Linux addition. The BSDs have kqueue which according to
| some people is actually better [cf.
| https://www.youtube.com/embed/l6XQUciI-Sc?start=3362 ]. But
| kqueue isn't POSIX either. Only poll() and select() are...
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