<feed xmlns='http://www.w3.org/2005/Atom'>
<title>linux-toradex.git/include/rdma/rdmavt_qp.h, branch v4.9.33</title>
<subtitle>Linux kernel for Apalis and Colibri modules</subtitle>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/'/>
<entry>
<title>IB/rdmavt: Add functions to get and release QP references</title>
<updated>2016-09-16T18:35:27+00:00</updated>
<author>
<name>Mike Marciniszyn</name>
<email>mike.marciniszyn@intel.com</email>
</author>
<published>2016-09-06T11:34:21+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=4107b8a029995e4a2c928b395a12ebc67d8e3689'/>
<id>4107b8a029995e4a2c928b395a12ebc67d8e3689</id>
<content type='text'>
This centralizes the function and improves code readability.

Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
This centralizes the function and improves code readability.

Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>IB/rdmavt: Eliminate redundant opcode test in mr ref clear</title>
<updated>2016-08-03T02:46:21+00:00</updated>
<author>
<name>Ira Weiny</name>
<email>ira.weiny@intel.com</email>
</author>
<published>2016-07-28T01:07:36+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=fe508272c963d62de4183c32b6883c3d54c557ef'/>
<id>fe508272c963d62de4183c32b6883c3d54c557ef</id>
<content type='text'>
The use of the specific opcode test is redundant since
all ack entry users correctly manipulate the mr pointer
to selectively trigger the reference clearing.

The overly specific test hinders the use of implementation
specific operations.

The change needs to get rid of the union to insure that
an atomic value is not seen as an MR pointer.

Reviewed-by: Ashutosh Dixit &lt;ashutosh.dixit@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Ira Weiny &lt;ira.weiny@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
The use of the specific opcode test is redundant since
all ack entry users correctly manipulate the mr pointer
to selectively trigger the reference clearing.

The overly specific test hinders the use of implementation
specific operations.

The change needs to get rid of the union to insure that
an atomic value is not seen as an MR pointer.

Reviewed-by: Ashutosh Dixit &lt;ashutosh.dixit@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Ira Weiny &lt;ira.weiny@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>IB/rdmavt, hfi1: Fix NFSoRDMA failure with FRMR enabled</title>
<updated>2016-08-02T20:00:58+00:00</updated>
<author>
<name>Jianxin Xiong</name>
<email>jianxin.xiong@intel.com</email>
</author>
<published>2016-07-25T20:39:45+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=d9b13c203003cfb78c1f216049a204d385ccaeff'/>
<id>d9b13c203003cfb78c1f216049a204d385ccaeff</id>
<content type='text'>
Hanging has been observed while writing a file over NFSoRDMA. Dmesg on
the server contains messages like these:

[  931.992501] svcrdma: Error -22 posting RDMA_READ
[  952.076879] svcrdma: Error -22 posting RDMA_READ
[  982.154127] svcrdma: Error -22 posting RDMA_READ
[ 1012.235884] svcrdma: Error -22 posting RDMA_READ
[ 1042.319194] svcrdma: Error -22 posting RDMA_READ

Here is why:

With the base memory management extension enabled, FRMR is used instead
of FMR. The xprtrdma server issues each RDMA read request as the following
bundle:

(1)IB_WR_REG_MR, signaled;
(2)IB_WR_RDMA_READ, signaled;
(3)IB_WR_LOCAL_INV, signaled &amp; fencing.

These requests are signaled. In order to generate completion, the fast
register work request is processed by the hfi1 send engine after being
posted to the work queue, and the corresponding lkey is not valid until
the request is processed. However, the rdmavt driver validates lkey when
the RDMA read request is posted and thus it fails immediately with error
-EINVAL (-22).

This patch changes the work flow of local operations (fast register and
local invalidate) so that fast register work requests are always
processed immediately to ensure that the corresponding lkey is valid
when subsequent work requests are posted. Local invalidate requests are
processed immediately if fencing is not required and no previous local
invalidate request is pending.

To allow completion generation for signaled local operations that have
been processed before posting to the work queue, an internal send flag
RVT_SEND_COMPLETION_ONLY is added. The hfi1 send engine checks this flag
and only generates completion for such requests.

Reviewed-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Jianxin Xiong &lt;jianxin.xiong@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Hanging has been observed while writing a file over NFSoRDMA. Dmesg on
the server contains messages like these:

[  931.992501] svcrdma: Error -22 posting RDMA_READ
[  952.076879] svcrdma: Error -22 posting RDMA_READ
[  982.154127] svcrdma: Error -22 posting RDMA_READ
[ 1012.235884] svcrdma: Error -22 posting RDMA_READ
[ 1042.319194] svcrdma: Error -22 posting RDMA_READ

Here is why:

With the base memory management extension enabled, FRMR is used instead
of FMR. The xprtrdma server issues each RDMA read request as the following
bundle:

(1)IB_WR_REG_MR, signaled;
(2)IB_WR_RDMA_READ, signaled;
(3)IB_WR_LOCAL_INV, signaled &amp; fencing.

These requests are signaled. In order to generate completion, the fast
register work request is processed by the hfi1 send engine after being
posted to the work queue, and the corresponding lkey is not valid until
the request is processed. However, the rdmavt driver validates lkey when
the RDMA read request is posted and thus it fails immediately with error
-EINVAL (-22).

This patch changes the work flow of local operations (fast register and
local invalidate) so that fast register work requests are always
processed immediately to ensure that the corresponding lkey is valid
when subsequent work requests are posted. Local invalidate requests are
processed immediately if fencing is not required and no previous local
invalidate request is pending.

To allow completion generation for signaled local operations that have
been processed before posting to the work queue, an internal send flag
RVT_SEND_COMPLETION_ONLY is added. The hfi1 send engine checks this flag
and only generates completion for such requests.

Reviewed-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Jianxin Xiong &lt;jianxin.xiong@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>IB/hfi1: Add the capability for reserved operations</title>
<updated>2016-08-02T20:00:58+00:00</updated>
<author>
<name>Mike Marciniszyn</name>
<email>mike.marciniszyn@intel.com</email>
</author>
<published>2016-07-25T20:39:39+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=856cc4c237add46510c8ae91764f4eda31a9e1cf'/>
<id>856cc4c237add46510c8ae91764f4eda31a9e1cf</id>
<content type='text'>
This fix allows for support of in-kernel reserved operations
without impacting the ULP user.

The low level driver can register a non-zero value which
will be transparently added to the send queue size and hidden
from the ULP in every respect.

ULP post sends will never see a full queue due to a reserved
post send and reserved operations will never exceed that
registered value.

The s_avail will continue to track the ULP swqe availability
and the difference between the reserved value and the reserved
in use will track reserved availabity.

Reviewed-by: Ashutosh Dixit &lt;ashutosh.dixit@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
This fix allows for support of in-kernel reserved operations
without impacting the ULP user.

The low level driver can register a non-zero value which
will be transparently added to the send queue size and hidden
from the ULP in every respect.

ULP post sends will never see a full queue due to a reserved
post send and reserved operations will never exceed that
registered value.

The s_avail will continue to track the ULP swqe availability
and the difference between the reserved value and the reserved
in use will track reserved availabity.

Reviewed-by: Ashutosh Dixit &lt;ashutosh.dixit@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>IB/rdmavt: Handle local operations in post send</title>
<updated>2016-08-02T20:00:58+00:00</updated>
<author>
<name>Jianxin Xiong</name>
<email>jianxin.xiong@intel.com</email>
</author>
<published>2016-07-25T20:38:25+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=d9f8723924d5955979d05cb7f4f10d9ebac39b7d'/>
<id>d9f8723924d5955979d05cb7f4f10d9ebac39b7d</id>
<content type='text'>
Some work requests are local operations, such as IB_WR_REG_MR and
IB_WR_LOCAL_INV. They differ from non-local operations in that:

(1) Local operations can be processed immediately without being posted
to the send queue if neither fencing nor completion generation is needed.
However, to ensure correct ordering, once a local operation is posted to
the work queue due to fencing or completion requiement, all subsequent
local operations must also be posted to the work queue until all the
local operations on the work queue have completed.

(2) Local operations don't send packets over the wire and thus don't
need (and shouldn't update) the packet sequence numbers.

Define a new a flag bit for the post send table to identify local
operations.

Add a new field to the QP structure to track the number of local
operations on the send queue to determine if direct processing of new
local operations should be enabled/disabled.

Reviewed-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Jianxin Xiong &lt;jianxin.xiong@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Some work requests are local operations, such as IB_WR_REG_MR and
IB_WR_LOCAL_INV. They differ from non-local operations in that:

(1) Local operations can be processed immediately without being posted
to the send queue if neither fencing nor completion generation is needed.
However, to ensure correct ordering, once a local operation is posted to
the work queue due to fencing or completion requiement, all subsequent
local operations must also be posted to the work queue until all the
local operations on the work queue have completed.

(2) Local operations don't send packets over the wire and thus don't
need (and shouldn't update) the packet sequence numbers.

Define a new a flag bit for the post send table to identify local
operations.

Add a new field to the QP structure to track the number of local
operations on the send queue to determine if direct processing of new
local operations should be enabled/disabled.

Reviewed-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Jianxin Xiong &lt;jianxin.xiong@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>IB/rdmavt: Add data structures and routines for table driven post send</title>
<updated>2016-08-02T19:47:44+00:00</updated>
<author>
<name>Mike Marciniszyn</name>
<email>mike.marciniszyn@intel.com</email>
</author>
<published>2016-07-01T23:02:07+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=afcf8f7647780aa147ad68be48d223cd50311b9a'/>
<id>afcf8f7647780aa147ad68be48d223cd50311b9a</id>
<content type='text'>
Add flexibility for driver dependent operations in post send
because different drivers will have differing post send
operation support.

This includes data structure definitions to support a table
driven scheme along with the necessary validation routine
using the new table.

Reviewed-by: Ashutosh Dixit &lt;ashutosh.dixit@intel.com&gt;
Reviewed-by: Jianxin Xiong &lt;jianxin.xiong@intel.com&gt;
Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Add flexibility for driver dependent operations in post send
because different drivers will have differing post send
operation support.

This includes data structure definitions to support a table
driven scheme along with the necessary validation routine
using the new table.

Reviewed-by: Ashutosh Dixit &lt;ashutosh.dixit@intel.com&gt;
Reviewed-by: Jianxin Xiong &lt;jianxin.xiong@intel.com&gt;
Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>IB/rdamvt: Fix rdmavt s_ack_queue sizing</title>
<updated>2016-05-26T16:21:10+00:00</updated>
<author>
<name>Mike Marciniszyn</name>
<email>mike.marciniszyn@intel.com</email>
</author>
<published>2016-05-24T19:50:40+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=8b103e9cdee5f381bc20a8a9f9bb5be11de8e68f'/>
<id>8b103e9cdee5f381bc20a8a9f9bb5be11de8e68f</id>
<content type='text'>
rdmavt allows the driver to specify the size of the ack queue, but
only uses it for the modify QP limit testing for setting the atomic
limit value.

The driver dependent size is now used to size the s_ack_queue ring
dynamicially.

Since the driver knows its size, the driver will use its define
for any ring size dependent code.

Reviewed-by: Mitko Haralanov &lt;mitko.haralanov@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
rdmavt allows the driver to specify the size of the ack queue, but
only uses it for the modify QP limit testing for setting the atomic
limit value.

The driver dependent size is now used to size the s_ack_queue ring
dynamicially.

Since the driver knows its size, the driver will use its define
for any ring size dependent code.

Reviewed-by: Mitko Haralanov &lt;mitko.haralanov@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>IB/rdmavt: Fix adaptive pio hang</title>
<updated>2016-04-28T20:32:26+00:00</updated>
<author>
<name>Mike Marciniszyn</name>
<email>mike.marciniszyn@intel.com</email>
</author>
<published>2016-04-12T17:45:51+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=f39cc34df7ed919c5c7630a8a7a701939356c37c'/>
<id>f39cc34df7ed919c5c7630a8a7a701939356c37c</id>
<content type='text'>
The RVT_S_WAIT_PIO_DRAIN flag was missing from
the set of flags indicating a qp is waiting
on a resource.

This caused the sleep/wakeup for adaptive pio
drain to lose a wakeup "hanging" a QP.

Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
The RVT_S_WAIT_PIO_DRAIN flag was missing from
the set of flags indicating a qp is waiting
on a resource.

This caused the sleep/wakeup for adaptive pio
drain to lose a wakeup "hanging" a QP.

Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>IB/hfi1: Report pid in qp_stats to aid debug</title>
<updated>2016-03-17T19:55:19+00:00</updated>
<author>
<name>Mike Marciniszyn</name>
<email>mike.marciniszyn@intel.com</email>
</author>
<published>2016-03-07T19:35:08+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=ef086c0d5dd9a151578c72b6f257e5b0e77d65eb'/>
<id>ef086c0d5dd9a151578c72b6f257e5b0e77d65eb</id>
<content type='text'>
Tracking user/QP ownership is needed to debug issues with
user ULPs like OpenMPI.

Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
Tracking user/QP ownership is needed to debug issues with
user ULPs like OpenMPI.

Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
</div>
</content>
</entry>
<entry>
<title>staging/rdma/hfi1: Adaptive PIO for short messages</title>
<updated>2016-03-11T01:38:14+00:00</updated>
<author>
<name>Mike Marciniszyn</name>
<email>mike.marciniszyn@intel.com</email>
</author>
<published>2016-02-14T20:45:36+00:00</published>
<link rel='alternate' type='text/html' href='https://git.toradex.cn/cgit/linux-toradex.git/commit/?id=14553ca11039732bcba3c160a26d702dbe71dd49'/>
<id>14553ca11039732bcba3c160a26d702dbe71dd49</id>
<content type='text'>
The change requires a new pio_busy field in the iowait structure to
track the number of outstanding pios.  The new counter together
with the sdma counter serve as the basis for a packet by packet decision
as to which egress mechanism to use.  Since packets given to different
egress mechanisms are not ordered, this scheme will preserve the order.

The iowait drain/wait mechanisms are extended for a pio case.  An
additional qp wait flag is added for the PIO drain wait case.

Currently the only pio wait is for buffers, so the no_bufs_available()
routine name is changed to pio_wait() and a third argument is passed
with one of the two pio wait flags to generalize the routine.  A module
parameter is added to hold a configurable threshold. For now, the
module parameter is zero.

A heuristic routine is added to return the func pointer of the proper
egress routine to use.

The heuristic is as follows:
- SMI always uses pio
- GSI,UD qps &lt;= threshold use pio
- UD qps &gt; threadhold use sdma
  o No coordination with sdma is required because order is not required
    and this qp pio count is not maintained for UD
- RC/UC ONLY packets &lt;= threshold chose as follows:
  o If sdmas pending, use SDMA
  o Otherwise use pio and enable the pio tracking count at
    the time the pio buffer is allocated
- RC/UC ONLY packets &gt; threshold use SDMA
  o If pio's are pending the pio_wait with the new wait flag is
    called to delay for pios to drain

The threshold is potentially reduced by the QP's mtu.

The sc_buffer_alloc() has two additional args (a callback, a void *)
which are exploited by the RC/UC cases to pass a new complete routine
and a qp *.

When the shadow ring completes the credit associated with a packet,
the new complete routine is called.  The verbs_pio_complete() will then
decrement the busy count and trigger any drain waiters in qp destroy
or reset.

Reviewed-by: Jubin John &lt;jubin.john@intel.com&gt;
Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</content>
<content type='xhtml'>
<div xmlns='http://www.w3.org/1999/xhtml'>
<pre>
The change requires a new pio_busy field in the iowait structure to
track the number of outstanding pios.  The new counter together
with the sdma counter serve as the basis for a packet by packet decision
as to which egress mechanism to use.  Since packets given to different
egress mechanisms are not ordered, this scheme will preserve the order.

The iowait drain/wait mechanisms are extended for a pio case.  An
additional qp wait flag is added for the PIO drain wait case.

Currently the only pio wait is for buffers, so the no_bufs_available()
routine name is changed to pio_wait() and a third argument is passed
with one of the two pio wait flags to generalize the routine.  A module
parameter is added to hold a configurable threshold. For now, the
module parameter is zero.

A heuristic routine is added to return the func pointer of the proper
egress routine to use.

The heuristic is as follows:
- SMI always uses pio
- GSI,UD qps &lt;= threshold use pio
- UD qps &gt; threadhold use sdma
  o No coordination with sdma is required because order is not required
    and this qp pio count is not maintained for UD
- RC/UC ONLY packets &lt;= threshold chose as follows:
  o If sdmas pending, use SDMA
  o Otherwise use pio and enable the pio tracking count at
    the time the pio buffer is allocated
- RC/UC ONLY packets &gt; threshold use SDMA
  o If pio's are pending the pio_wait with the new wait flag is
    called to delay for pios to drain

The threshold is potentially reduced by the QP's mtu.

The sc_buffer_alloc() has two additional args (a callback, a void *)
which are exploited by the RC/UC cases to pass a new complete routine
and a qp *.

When the shadow ring completes the credit associated with a packet,
the new complete routine is called.  The verbs_pio_complete() will then
decrement the busy count and trigger any drain waiters in qp destroy
or reset.

Reviewed-by: Jubin John &lt;jubin.john@intel.com&gt;
Reviewed-by: Dennis Dalessandro &lt;dennis.dalessandro@intel.com&gt;
Signed-off-by: Mike Marciniszyn &lt;mike.marciniszyn@intel.com&gt;
Signed-off-by: Doug Ledford &lt;dledford@redhat.com&gt;
</pre>
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