Hi-
Shirley Ma and I are reviving work on the NFS/RDMA client code base in the Linux kernel. So far we?ve built and run functional tests to determine what is working and what is broken.
One complication is the number of memory registration modes supported by the RPC/RDMA transport: there are seven. These were added over the years to support particular HCAs or as proof-of-concept. The transport chooses a registration mode at mount time based on what the link HCA supports.
Not all HCAs support all memory registration modes, so our test matrix is quite large. I?d like to propose removing support for one or more of these memory registration modes in the name of making it easier to change this code and test it without breaking something that we can?t test.
BOUNCEBUFFERS - All HCAs support this mode. Does not use RDMA READ and WRITE, and the client end copies data into place. RDMA is offloaded, by data copy is not. I?m told it was never intended for production use.
REGISTER - Safe but relatively slow. Uses reg_phys_mr verb which is not supported in mlx4/mlx5, but all other HCAs/providers can use this mode.
MEM_WINDOWS - Uses bind_mr verb. Safe, but supports only a narrow range of HCAs.
MEM_WINDOWS_ASYNC - Not always safe, and only a narrow range of HCAs is supported.
MTHCA_FMR - Uses alloc_fmr verb. Safe, reasonably fast, but only a narrow range of older HCAs is supported.
FRMR - Safe, generally fast. Currently the preferred registration mode, but is not supported with some older HCAs/providers.
ALLPHYSICAL - Usually fast, but not safe as it exposes client memory. All HCAs support this mode.
I propose removing BOUNCEBUFFERS since it is not intended for production use.
I propose removing ALLPHYSICAL and MEM_WINDOWS_ASYNC as they are not generally safe. RFC 5666 suggests that unsafe memory registration modes be avoided.
I propose removing MEM_WINDOWS as it adds complexity without adding a lot of HCA compatibility.
I propose removing MTHCA_FMR as I?m told it is hard to obtain HCAs we would need for testing this registration mode, and these are all old adapters anyway.
This leaves NFS/RDMA client support for REGISTER and FRMR, which should cover all existing HCAs, and it is easy to test both of these memory registration modes with just one or two well-picked HCAs.
We would contribute these changes to the client code base. The NFS/RDMA server code could use similar attention, but we are not volunteering to change it at this time.
Thoughts/comments?
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
-----Original Message-----
From: [email protected] [mailto:[email protected]] On Behalf Of Chuck Lever
Sent: Wednesday, February 26, 2014 11:45 AM
To: [email protected]; Linux NFS Mailing List
Cc: Shirley Ma
Subject: Proposal for simplifying NFS/RDMA client memory registration
Hi-
Shirley Ma and I are reviving work on the NFS/RDMA client code base in the Linux kernel. So far we've built and run functional tests to determine what is working and what is broken.
One complication is the number of memory registration modes supported by the RPC/RDMA transport: there are seven. These were added over the years to support particular HCAs or as proof-of-concept. The transport chooses a registration mode at mount time based on what the link HCA supports.
Not all HCAs support all memory registration modes, so our test matrix is quite large. I'd like to propose removing support for one or more of these memory registration modes in the name of making it easier to change this code and test it without breaking something that we can't test.
BOUNCEBUFFERS - All HCAs support this mode. Does not use RDMA READ and WRITE, and the client end copies data into place. RDMA is offloaded, by data copy is not. I'm told it was never intended for production use.
REGISTER - Safe but relatively slow. Uses reg_phys_mr verb which is not supported in mlx4/mlx5, but all other HCAs/providers can use this mode.
MEM_WINDOWS - Uses bind_mr verb. Safe, but supports only a narrow range of HCAs.
MEM_WINDOWS_ASYNC - Not always safe, and only a narrow range of HCAs is supported.
MTHCA_FMR - Uses alloc_fmr verb. Safe, reasonably fast, but only a narrow range of older HCAs is supported.
FRMR - Safe, generally fast. Currently the preferred registration mode, but is not supported with some older HCAs/providers.
ALLPHYSICAL - Usually fast, but not safe as it exposes client memory. All HCAs support this mode.
I propose removing BOUNCEBUFFERS since it is not intended for production use.
I propose removing ALLPHYSICAL and MEM_WINDOWS_ASYNC as they are not generally safe. RFC 5666 suggests that unsafe memory registration modes be avoided.
I propose removing MEM_WINDOWS as it adds complexity without adding a lot of HCA compatibility.
I propose removing MTHCA_FMR as I'm told it is hard to obtain HCAs we would need for testing this registration mode, and these are all old adapters anyway.
This leaves NFS/RDMA client support for REGISTER and FRMR, which should cover all existing HCAs, and it is easy to test both of these memory registration modes with just one or two well-picked HCAs.
We would contribute these changes to the client code base. The NFS/RDMA server code could use similar attention, but we are not volunteering to change it at this time.
[sf] We need volunteers for server too as the optimizations on client only may not be enough considering that SMB express optimized both sides. Maybe we can find a student of Erez to work on this. Thanks
./Sorin
Thoughts/comments?
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
On 2/26/2014 8:44 AM, Chuck Lever wrote:
> Hi-
>
> Shirley Ma and I are reviving work on the NFS/RDMA client code base in the Linux kernel. So far we?ve built and run functional tests to determine what is working and what is broken.
>
> One complication is the number of memory registration modes supported by the RPC/RDMA transport: there are seven. These were added over the years to support particular HCAs or as proof-of-concept. The transport chooses a registration mode at mount time based on what the link HCA supports.
>
> Not all HCAs support all memory registration modes, so our test matrix is quite large. I?d like to propose removing support for one or more of these memory registration modes in the name of making it easier to change this code and test it without breaking something that we can?t test.
>
> BOUNCEBUFFERS - All HCAs support this mode. Does not use RDMA READ and WRITE, and the client end copies data into place. RDMA is offloaded, by data copy is not. I?m told it was never intended for production use.
>
> REGISTER - Safe but relatively slow. Uses reg_phys_mr verb which is not supported in mlx4/mlx5, but all other HCAs/providers can use this mode.
>
> MEM_WINDOWS - Uses bind_mr verb. Safe, but supports only a narrow range of HCAs.
>
> MEM_WINDOWS_ASYNC - Not always safe, and only a narrow range of HCAs is supported.
>
> MTHCA_FMR - Uses alloc_fmr verb. Safe, reasonably fast, but only a narrow range of older HCAs is supported.
The MTHCA FMR is not completely safe - it protects only on page
boundaries, therefore the neighboring bytes are vulnerable to
silent corruption (reads) and exposure (write).
It is quite correct that they are supported on only a specific
set of legacy Mellanox HCA. You should consider removing the
code that looked for this PCI ID and attempted to alter the
device's wire MTU, to overcome another of its limitations.
>
> FRMR - Safe, generally fast. Currently the preferred registration mode, but is not supported with some older HCAs/providers.
This should be, by far, the preferred mode. Also, if I recall
correctly, the server depends on this mode being available/supported.
However, it may not be supported by Soft iWARP. Physical addressing
is used.
>
> ALLPHYSICAL - Usually fast, but not safe as it exposes client memory. All HCAs support this mode.
Not safe is an understatement. It exposes all of client physical
memory to the peer, for both read and write. A simple pointer error
on the server will silently corrupt the client. This mode was
intended only for testing, and in experimental deployments.
Tom.
>
>
> I propose removing BOUNCEBUFFERS since it is not intended for production use.
>
> I propose removing ALLPHYSICAL and MEM_WINDOWS_ASYNC as they are not generally safe. RFC 5666 suggests that unsafe memory registration modes be avoided.
>
> I propose removing MEM_WINDOWS as it adds complexity without adding a lot of HCA compatibility.
>
> I propose removing MTHCA_FMR as I?m told it is hard to obtain HCAs we would need for testing this registration mode, and these are all old adapters anyway.
>
> This leaves NFS/RDMA client support for REGISTER and FRMR, which should cover all existing HCAs, and it is easy to test both of these memory registration modes with just one or two well-picked HCAs.
>
> We would contribute these changes to the client code base. The NFS/RDMA server code could use similar attention, but we are not volunteering to change it at this time.
>
> Thoughts/comments?
>
> --
> Chuck Lever
> chuck[dot]lever[at]oracle[dot]com
>
>
>
> --
> To unsubscribe from this list: send the line "unsubscribe linux-nfs" in
> the body of a message to [email protected]
> More majordomo info at http://vger.kernel.org/majordomo-info.html
>
>
On Mon, Mar 3, 2014 at 11:54 AM, faibish, sorin <[email protected]> wrote:
>
> > On Mar 3, 2014, at 7:09 PM, "Christoph Hellwig" <[email protected]> wrote:
> >
> >> On Mon, Mar 03, 2014 at 12:02:33PM -0500, Chuck Lever wrote:
> >> All HCAs in 3.13 (and rxe) can support either MTHCA_FMR or FRMR or both. Wendy?s HCA supports only ALLPHYSICAL.
> >
> > Is Wendy planning to submit her HCA driver ASAP? If not there's not
> > reason to keep ALLPHYSICAL either.
> I second Christoph. Legacy is good as long as there are users of Linux with the legacy server. I would say that the only reason to keep it is if Linux server will support it. Same we apply to Lustre client in kernel.
>
> ./Sorin
>
> >
> >> Does it make sense to deprecate then remove the registration modes in the first list?
> >
> > Yes.
> >
>
After discussing this with my manager, we'll let it go for now ...
will re-submit the full patch set in the future when we finalize the
plan.
Thanks,
Wendy
On Feb 26, 2014, at 11:44 AM, Chuck Lever <[email protected]> wrote:
> Hi-
>
> Shirley Ma and I are reviving work on the NFS/RDMA client code base in the Linux kernel. So far we?ve built and run functional tests to determine what is working and what is broken.
>
> One complication is the number of memory registration modes supported by the RPC/RDMA transport: there are seven. These were added over the years to support particular HCAs or as proof-of-concept. The transport chooses a registration mode at mount time based on what the link HCA supports.
>
> Not all HCAs support all memory registration modes, so our test matrix is quite large. I?d like to propose removing support for one or more of these memory registration modes in the name of making it easier to change this code and test it without breaking something that we can?t test.
>
> BOUNCEBUFFERS - All HCAs support this mode. Does not use RDMA READ and WRITE, and the client end copies data into place. RDMA is offloaded, by data copy is not. I?m told it was never intended for production use.
>
> REGISTER - Safe but relatively slow. Uses reg_phys_mr verb which is not supported in mlx4/mlx5, but all other HCAs/providers can use this mode.
>
> MEM_WINDOWS - Uses bind_mr verb. Safe, but supports only a narrow range of HCAs.
>
> MEM_WINDOWS_ASYNC - Not always safe, and only a narrow range of HCAs is supported.
>
> MTHCA_FMR - Uses alloc_fmr verb. Safe, reasonably fast, but only a narrow range of older HCAs is supported.
>
> FRMR - Safe, generally fast. Currently the preferred registration mode, but is not supported with some older HCAs/providers.
>
> ALLPHYSICAL - Usually fast, but not safe as it exposes client memory. All HCAs support this mode.
>
>
> I propose removing BOUNCEBUFFERS since it is not intended for production use.
>
> I propose removing ALLPHYSICAL and MEM_WINDOWS_ASYNC as they are not generally safe. RFC 5666 suggests that unsafe memory registration modes be avoided.
>
> I propose removing MEM_WINDOWS as it adds complexity without adding a lot of HCA compatibility.
>
> I propose removing MTHCA_FMR as I?m told it is hard to obtain HCAs we would need for testing this registration mode, and these are all old adapters anyway.
>
> This leaves NFS/RDMA client support for REGISTER and FRMR, which should cover all existing HCAs, and it is easy to test both of these memory registration modes with just one or two well-picked HCAs.
>
> We would contribute these changes to the client code base. The NFS/RDMA server code could use similar attention, but we are not volunteering to change it at this time.
>
> Thoughts/comments?
Karma score so far:
BOUNCEBUFFERS, REGISTER, MEM_WINDOWS, MEM_WINDOWS_ASYNC - no votes in favor of keeping
MTHCA_FMR, FRMR, ALLPHYSICAL - one or more votes in favor of keeping
All HCAs in 3.13 (and rxe) can support either MTHCA_FMR or FRMR or both. Wendy?s HCA supports only ALLPHYSICAL.
Does it make sense to deprecate then remove the registration modes in the first list?
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
On Mon, Mar 03, 2014 at 12:02:33PM -0500, Chuck Lever wrote:
> All HCAs in 3.13 (and rxe) can support either MTHCA_FMR or FRMR or both. Wendy?s HCA supports only ALLPHYSICAL.
Is Wendy planning to submit her HCA driver ASAP? If not there's not
reason to keep ALLPHYSICAL either.
> Does it make sense to deprecate then remove the registration modes in the first list?
Yes.
On Mar 1, 2014, at 11:00 AM, Jeff Layton <[email protected]> wrote:
> On Fri, 28 Feb 2014 21:59:00 -0500
> Chuck Lever <[email protected]> wrote:
>
>> Hi Wendy-
>>
>> On Feb 28, 2014, at 5:26 PM, Wendy Cheng <[email protected]> wrote:
>>
>>> On Fri, Feb 28, 2014 at 2:20 PM, Wendy Cheng <[email protected]> wrote:
>>>> ni i...On Fri, Feb 28, 2014 at 1:41 PM, Tom Talpey <[email protected]> wrote:
>>>>>
>>>>> On 2/26/2014 8:44 AM, Chuck Lever wrote:
>>>>>>
>>>>>> Hi-
>>>>>>
>>>>>> Shirley Ma and I are reviving work on the NFS/RDMA client code base in
>>>>>> the Linux kernel. So far we've built and run functional tests to determine
>>>>>> what is working and what is broken.
>>>>>>
>>>>>> [snip]
>>>>
>>>>
>>>>>>
>>>>>> ALLPHYSICAL - Usually fast, but not safe as it exposes client memory.
>>>>>> All HCAs support this mode.
>>>>>
>>>>>
>>>>> Not safe is an understatement. It exposes all of client physical
>>>>> memory to the peer, for both read and write. A simple pointer error
>>>>> on the server will silently corrupt the client. This mode was
>>>>> intended only for testing, and in experimental deployments.
>>>
>>> (sorry, resend .. previous reply bounced back due to gmail html format)
>>>
>>> Please keep "ALLPHYSICAL" for now - as our embedded system needs it.
>>
>> This is just the client side. Confirming that you still need support for the ALLPHYSICAL memory registration mode in the NFS/RDMA client.
>>
>> Do you have plans to move to a mode that is less risky? If not, can we depend on you to perform regular testing with ALLPHYSICAL as we update the client code? Do you have any bug fixes you?d like to merge upstream?
>>
>
> Also, given that ALLPHYSICAL isn't considered safe, we should at the
> very least require some sort of explicit opt-in before allowing it to be
> used. Perhaps either a Kconfig option, or maybe a runtime switch like a
> module parm?
Well, there is already an opt-in: /proc/sys/sunrpc/rdma_memreg_strategy
selects the default registration mode. Currently FRMR is always used
unless the HCA doesn?t support it.
If we need to keep ALLPHYSICAL, the least thing I would want to do is
remove the logic in rpcrdma_ia_open() that switches to ALLPHYSICAL if
the mode selected by rdma_memreg_strategy isn?t supported by the HCA.
--
Chuck Lever
chuck[dot]lever[at]oracle[dot]com
Sent from my iPad
> On Mar 3, 2014, at 7:09 PM, "Christoph Hellwig" <[email protected]> wrote:
>
>> On Mon, Mar 03, 2014 at 12:02:33PM -0500, Chuck Lever wrote:
>> All HCAs in 3.13 (and rxe) can support either MTHCA_FMR or FRMR or both. Wendy?s HCA supports only ALLPHYSICAL.
>
> Is Wendy planning to submit her HCA driver ASAP? If not there's not
> reason to keep ALLPHYSICAL either.
I second Christoph. Legacy is good as long as there are users of Linux with the legacy server. I would say that the only reason to keep it is if Linux server will support it. Same we apply to Lustre client in kernel.
./Sorin
>
>> Does it make sense to deprecate then remove the registration modes in the first list?
>
> Yes.
>
> --
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