Hi Shahar,

I asked a question to you because our team may be interested in that. But that is outside of open source and spdk. Hence you can ignore that.

What I can say is your use case of spdk may not be unique and may attract any interest.

Thanks again,
Shuhei 


2018年5月9日(水) 17:43 松本周平 / MATSUMOTO,SHUUHEI <shuhei.matsumoto.xt@hitachi.com>:

Hi Shahar,


Thank you for your interesting proposal and excuse me for cutting in the thread.

Do you have any plan to use similar or better mechanism between your application and another backend SPDK bdev or device driver (e.g. nvme, bdev_nvme) ?


Thanks,

Shuhei



差出人: SPDK <spdk-bounces@lists.01.org> が Shahar Salzman <shahar.salzman@kaminario.com> の代理で送信
送信日時: 2018年5月9日 16:48:37
宛先: spdk@lists.01.org
件名: [!]Re: [SPDK] SPDK + user space appliance
 

Hi Ben,


To answer your question first, the main reason to have a generic spdk IO API for storage appliance is being able to maintain functionality over versions.

We started with our module in version 17.07, but when we started integrating it into 17.07.01, and the 18.X version we started running into issues. Since the bdev layer is internal to spdk, it makes sense that it will change both in functionality and in interface from time to time especially in NVMeF where the specifications are so young, which is the reason that we would like to have an API which is more stable over versions.

As a storage appliance, the requirements are fairly stable, and at least in the case of SCSI, a thin "glue API" had been enough to get the core appliance work with multiple frontend targets (e.g. both SCSI and internal replication). I believe that the same method can be applied to NVMEF.

In addition, I think that our use case is not unique to the way we are integrating spdk, which means that the work we put in can benefit other users, and hopefully via their experience, the code can become more robust and useful.


Shahar


From: SPDK <spdk-bounces@lists.01.org> on behalf of Walker, Benjamin <benjamin.walker@intel.com>
Sent: Tuesday, May 8, 2018 8:30:20 PM
To: spdk@lists.01.org
Subject: Re: [SPDK] SPDK + user space appliance
 
On Tue, 2018-05-08 at 07:36 +0000, Shahar Salzman wrote:
> Hi Jim and Ben,
>
> For the threading issue, I agree that there is something not very clean in the
> interface, as there is an assumption on how the user implements it. As I did
> in the bdev_user_example, we also use a ring in order to place all the
> incoming IO without delaying the reactor, and then use multiple pollers to
> actually handle the IO (deduplication, compression, HA etc.). This is why
> there are 2 distinct interfaces - submit_io callback, and
> the bdev_user_submit_completion interface which (normally) is called on
> another thread (not the original poller), and passed back to the reactor via
> the completion queue on the bdev_user_io_channel, and the registered poller
> thread which takes from the user completion queue.
> Do you think that a cleaner interface would be modifying the submit_io
> callback to a poll_io interface which checks a bdev_user internal ring for IO?
> Or do you think that the current interface is OK provided good documentation?
>
> Regarding the spdk_call_unaffinitized, I am currently using spdk_event_call in
> order to register my volumes, I don't really like this since it forces me to
> (eventually) add another async callback in my app to verify that device
> registration was successful (and this just adds more conditions, futures etc.
> in the application). Is there a way to call spdk interfaces directly with a
> "non-spdk" thread (i.e. TLS is not initialized)?

I'm not so much concerned yet with the interface you've defined, but rather
understanding the whole approach at a high level. The SPDK bdev layer is
designed for custom bdev modules to be added, so my primary question is why
write a generic bdev_user module as opposed to writing a "your custom storage
backend" module? I think this is the key piece, and understanding the process
you went through as you designed this will probably yield a whole bunch of good
improvements to the current bdev module system.

Thanks,
Ben


>
> Hope this answers the questions,
> Shahar



> From: SPDK <spdk-bounces@lists.01.org> on behalf of Harris, James R
> <james.r.harris@intel.com>
> Sent: Monday, May 7, 2018 9:18:20 PM
> To: Storage Performance Development Kit
> Subject: Re: [SPDK] SPDK + user space appliance

> There are also calls such as spdk_call_unaffinitized() and
> spdk_unaffinitize_thread() which have been added to enable cases where a bdev
> module may need to spawn non-polling threads and don’t want those threads to
> inherit the affinity of the calling thread.  The SPDK rbd module currently
> uses these (see git commit fa5206c4) since rbd_open is a blocking call.  (Note
> that librbd does now support rbd_aio_open which is better suited for SPDK.)
>
> -Jim
>
>
> On 5/7/18, 11:02 AM, "SPDK on behalf of Walker, Benjamin" <spdk-bounces@lists.
> 01.org on behalf of benjamin.walker@intel.com> wrote:
>
>     Hi Shahar,
>    
>     Thank you for submitting the patch. I've looked through it in detail and I
> think
>     I understand the purpose of this code, but I'm going to explain it back to
> you
>     so you can correct me where I'm wrong.
>    
>     I think this code solves two distinct problems:
>    
>     1) You need to forward I/O out of the bdev layer to some custom backend,
> and you
>     want the code that does that to live outside of the SPDK repository.
>    
>     2) Your custom back-end library isn't suitable for use in a run-to-
> completion
>     model. By that I mean that you can't just call your library directly on
> the
>     thread that originally receives the spdk_bdev_io request because your
> library
>     either blocks or generally takes too long to return from the submission
> call
>     (maybe it is doing inline compression or something). Instead, you need to
>     shuttle those requests off to separate threads for handling.
>    
>     As far as point #1, today the SPDK build system does not nicely
> accommodate bdev
>     modules whose code lives outside of SPDK. SPDK expects them to be in
>     lib/bdev/<module_name>. However, that's a fairly straightforward change to
> the
>     build system and it's one we've been intending to make for some time.
>    
>     For point #2, this is likely the case for a large number of storage back-
> ends,
>     but I think the proper way to solve it is probably back-end specific and
> not
>     general purpose. As a counter-point, SPDK already integrates with a number
> of
>     third-party storage back-ends today (Ceph RBD, libiscsi, libaio, etc.) and
> none
>     of those ended up needing to pass messages to other threads. They all
> support
>     asynchronous operations, though. I could imagine writing a bdev module
> that
>     ultimately makes POSIX preadv calls, for instance. That would need to be
>     implemented with a thread pool and each bdev_io gets funneled off to a
> thread in
>     the pool to perform the blocking operation.
>    
>     Ok - I explained what I think I'm understanding. Now tell me where I went
> wrong
>     :)
>    
>     Thanks,
>     Ben
>    
>     On Sun, 2018-05-06 at 10:32 +0000, Shahar Salzman wrote:
>     > Hi,
>     >
>     > I pushed the code for review, thanks Daniel for the help.
>     >
>     > In a nutshell:
>     > - bdev_user - an API for a user appliance to use spdk as an iSCSI/NVMeF
> target
>     > - bdev_user_example - reference application
>     > - The API relies on rings in order to submit/complete IOs
>     > - User appliance registers callbacks for submit_io (should we have
>     > read/write/other instead?)
>     > - User appliance registers its devices so that they may be added to an
>     > existing namespace (I am using RPC to do the management)
>     >
>     > Thanks,
>     > Shahar
>     >
>     >
>     > From: SPDK <spdk-bounces@lists.01.org> on behalf of Verkamp, Daniel
> <daniel.ve
>     > rkamp@intel.com>
>     > Sent: Thursday, May 3, 2018 8:50 PM
>     > To: Storage Performance Development Kit
>     > Subject: Re: [SPDK] SPDK + user space appliance
>     > 
>     > Hi Shahar,
>     > 
>     > The target branch for the push should be ‘refs/for/master’, not ‘master’
> – if
>     > you configured a remote as specified in http://www.spdk.io/development/
> it
>     > should look like:
>     > 
>     > [remote "review"]
>     >   url = https://review.gerrithub.io/spdk/spdk
>     >   push = HEAD:refs/for/master
>     > 
>     > From: SPDK [mailto:spdk-bounces@lists.01.org] On Behalf Of Shahar
> Salzman
>     > Sent: Thursday, May 3, 2018 1:00 AM
>     > To: Storage Performance Development Kit <spdk@lists.01.org>
>     > Subject: Re: [SPDK] SPDK + user space appliance
>     > 
>     > Hi Ben,
>     > 
>     > I have the code ready for review (spdk/master on dpdk/18.02), but I do
> not
>     > have push rights for gerrithub:
>     > shahar.salzman@shahars-vm:~/Kaminario/git/spdk$ git push spdk-review
>     > HEAD:master
>     > Password for 'https://ShaharSalzman-K@review.gerrithub.io':
>     > Counting objects: 109, done.
>     > Compressing objects: 100% (22/22), done.
>     > Writing objects: 100% (22/22), 8.70 KiB | 0 bytes/s, done.
>     > Total 22 (delta 14), reused 0 (delta 0)
>     > remote: Resolving deltas: 100% (14/14)
>     > remote: Branch refs/heads/master:
>     > remote: You are not allowed to perform this operation.
>     > remote: To push into this reference you need 'Push' rights.
>     > remote: User: ShaharSalzman-K
>     > remote: Please read the documentation and contact an administrator
>     > remote: if you feel the configuration is incorrect
>     > remote: Processing changes: refs: 1, done   
>     > To https://ShaharSalzman-K@review.gerrithub.io/a/spdk/spdk
>     >  ! [remote rejected] HEAD -> master (prohibited by Gerrit: ref update
> access
>     > denied)

> thub.i
>     > o/a/spdk/spdk'
>     > 
>     > Am I doing something incorrect, or is this just a permission issue?
>     > 
>     > Thanks,
>     > Shahar
>     > From: SPDK <spdk-bounces@lists.01.org> on behalf of Shahar Salzman
> <shahar.sal
>     > zman@kaminario.com>
>     > Sent: Wednesday, April 25, 2018 9:02:38 AM
>     > To: Storage Performance Development Kit
>     > Subject: Re: [SPDK] SPDK + user space appliance
>     > 
>     > Hi Ben,
>     > 
>     > The code is currently working on v17.07, we are planning on bumping the
>     > version to one of the latest stable versions (18.01?) + master.
>     > It will take me (hopefully) a few days to update the code and have our
>     > internal CI start running on this version, not sure it would be useful,
> but I
>     > can get our working 17.07 code (+ reference application) for review much
>     > faster.
>     > What is the best course of action?
>     > 
>     > Shahar
>     > From: SPDK <spdk-bounces@lists.01.org> on behalf of Walker, Benjamin
> <benjamin
>     > .walker@intel.com>
>     > Sent: Tuesday, April 24, 2018 7:19:12 PM
>     > To: Storage Performance Development Kit
>     > Subject: Re: [SPDK] SPDK + user space appliance
>     > 
>     > Hi Shahar,
>     > 
>     > Would you be willing to submit your bdev module as a patch on GerritHub?
> That
>     > way everyone can take a look and provide feedback. If you don’t want it
> to run
>     > the tests, you can put [RFC] and the beginning of the commit message.
>     > 
>     > Thanks,
>     > Ben
>     > 
>     > From: SPDK [mailto:spdk-bounces@lists.01.org] On Behalf Of Shahar
> Salzman
>     > Sent: Monday, April 23, 2018 8:45 AM
>     > To: spdk@lists.01.org
>     > Subject: Re: [SPDK] SPDK + user space appliance
>     > 
>     > Hi Ben,
>     > 
>     > Bumping this thread since I've been having some new thoughts on the
> issue now
>     > that we are starting integration with newer spdk versions.
>     > Unfortunately the merge isn't as smooth as I'd like it to be since the
> bdev
>     > module is pretty tightly integrated into spdk, perhaps we made some
> false
>     > assumptions writing the module, but it seems some of the newer spdk
> features
>     > are complicating the integration.
>     > My question is, if this passthrough module is useful, wouldn't it be
> better to
>     > maintain it as part of spdk so that we can catch issues as soon as they
> show
>     > up?
>     > We would be happy to help with maintaining this module, the module with
> is
>     > currently part of our CI with our "frozen" spdk version, but once
> integrated
>     > into the newer version we choose, I'll add it to the CI our CI as well.
>     > 
>     > Shahar
>     > From: SPDK <spdk-bounces@lists.01.org> on behalf of Walker, Benjamin
> <benjamin
>     > .walker@intel.com>
>     > Sent: Friday, February 2, 2018 11:43:58 PM
>     > To: spdk@lists.01.org
>     > Subject: Re: [SPDK] SPDK + user space appliance
>     > 
>     > On Thu, 2018-02-01 at 08:29 +0000, Shahar Salzman wrote:
>     > > Hi Ben,
>     > >
>     > > Would you also like to take a look at the bdev_user module?
>     > > It still needs some patching (as some of the stuff is still hard
> coded), but
>     > I
>     > > think we can get most of it cleaned up in a couple of days.
>     > >
>     > > In any case, is it the intention that the user write his own bdev
> module, or
>     > > would this user appliance glue be a useful generic module?
>     >
>     > For existing storage stacks that serve block I/O, like the internals of
> a SAN,
>     > the idea is that you write your own bdev module to forward I/O coming
> out of
>     > the
>     > SPDK bdev layer. Then you can use the SPDK iSCSI/NVMe-oF/vhost targets
> mostly
>     > as-is.
>     >
>     > In some cases, the actual iSCSI/NVMe-oF/vhost target applications won't
>     > integrate nicely directly into an existing storage application because
> they
>     > spawn their own threads and allocate their own memory. To support that,
> the
>     > libraries may be consumed directly instead of the applications
> (lib/iscsi,
>     > lib/scsi, lib/nvmf, etc.). The libraries don't spawn any of their own
> threads,
>     > but instead rely on SPDK's abstractions in include/spdk/io_channel.h.
> See
>     >
>     > http://www.spdk.io/doc/concurrency.html
>     >
>     > We don't currently have a way to write a custom bdev module that resides
>     > outside
>     > of the SPDK source tree, but it's very possible to add support for that.
> But
>     > beyond that inconvenience (just drop your module in lib/bdev for now),
> writing
>     > a
>     > bdev module is the recommended way of interacting with the bottom end of
> the
>     > SPDK bdev layer. I think that's what you really want to be doing in your
> code,
>     > from what I can tell.
>     >
>     > I hope that helps!
>     > _______________________________________________
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>     > SPDK@lists.01.org
>     > https://lists.01.org/mailman/listinfo/spdk
>     >
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