On 28-Mar-18 9:55 AM, Tan, Jianfeng wrote:
Hi Thomas and Harry,
On 3/28/2018 4:22 PM, Van Haaren, Harry wrote:
From: Thomas Monjalon [mailto:tho...@monjalon.net]
Sent: Wednesday, March 28, 2018 8:30 AM
To: Tan, Jianfeng <jianfeng....@intel.com>
Cc: Burakov, Anatoly <anatoly.bura...@intel.com>; dev@dpdk.org; Ananyev,
Konstantin <konstantin.anan...@intel.com>; Van Haaren, Harry
<harry.van.haa...@intel.com>
Subject: Re: [dpdk-dev] [PATCH v6 2/2] eal: add asynchronous request
API to
DPDK IPC
28/03/2018 04:08, Tan, Jianfeng:
Hi Thomas ,
From: Thomas Monjalon [mailto:tho...@monjalon.net]
27/03/2018 15:59, Anatoly Burakov:
Under the hood, we create a separate thread to deal with replies to
asynchronous requests, that will just wait to be notified by the
main thread, or woken up on a timer.
I really don't like that a library is creating a thread.
We don't even know where the thread is created (which core).
Can it be a rte_service? or in the interrupt thread?
Agree that we'd better not adding so many threads in a library.
I was considering to merge all the threads into the interrupt thread,
however, we don't have an interrupt thread in freebsd. Further, we don't
implement alarm API in freebsd. That's why I tend to current
implementation,
and optimize it later.
I would prefer we improve the current code now instead of polluting more
with more uncontrolled threads.
For rte_service, it may be not a good idea to reply on it as it needs
explicit API calls to setup.
I don't see the issue of the explicit API.
The IPC is a new service.
My concern is that not every DPDK application sets up rte_service, but
IPC will be used for very fundamental functions, like memory allocation.
We could not possibly ask all DPDK applications to add rte_service now.
And also take Harry's comments below into consideration, most likely, we
will move these threads into interrupt thread now by adding
Although I do like to see new services, if we want to enable "core"
dpdk functionality with Services, we need a proper designed solution
for that. Service cores is not intended for "occasional" work - there
is no method to block and sleep on a specific service until work
becomes available, so this would imply a busy-polling. Using a service
(hence busy polling) for rte_malloc()-based memory mapping requests is
inefficient, and total overkill :)
For this patch I suggest to use some blocking-read capable mechanism.
The problem here is that we add too many threads; blocking-read does not
decrease # of threads.
The above said, in the longer term it would be good to have a design
that allows new file-descriptors to be added to a "dpdk core" thread,
which performs occasional lengthy work if the FD has data available.
Interrupt thread vs rte_service, which is the direction to go? We
actually have some others threads, in vhost and even virtio-user; we can
also avoid those threads if we have a clear direction.
Thanks,
Jianfeng
Hi all,
First of all, @Thomas, this is not a "new library" - it's part of EAL.
We're going to be removing a few threads from EAL as it is because of
IPC (Jianfeng has already submitted patches for those), so i don't think
it's such a big deal to have two IPC threads instead of one. I'm open to
suggestions on how to make this work without a second thread, but i
don't see it.
We've discussed possibility of using rte_service internally, but decided
against it for reasons already outlined by Harry - it's not a suitable
mechanism for this kind of thing, not as it is.
Using interrupt thread for this _will_ work, however this will require a
a lot more changes, as currently alarm API allocates everything through
rte_malloc, while we want to use IPC for rte_malloc (which would make it
a circular dependency). So it'll probably be more API and more
complexity for dealing with malloc vs rte_malloc allocations. Hence the
least-bad approach taken here: a new thread.
--
Thanks,
Anatoly
