Add support for inter-domain DMA operations

This commit implements functions necessary to use inter-domain operations with idxd driver.

The process is as follows:

1. Process A that wishes to share its memory with others, shall call rte_idxd_window_create(), which will return a file descriptor
2. Process A is to send above mentioned file descriptor to any recipient process (usually over kernel IPC) that wishes to attach to that window
3. Process B, after receiving above mentioned file descriptor from process A over IPC, shall call rte_idxd_window_attach() and receive an inter-pasid handle
4. Process B shall use this handle as an argument for inter-domain operations using DMA device API

+};
--
2.37.2

Quoted 16 lines · Anatoly Burakov

This commit implements functions necessary to use inter-domain operations with idxd driver.

The process is as follows:

1. Process A that wishes to share its memory with others, shall call rte_idxd_window_create(), which will return a file descriptor
2. Process A is to send above mentioned file descriptor to any recipient process (usually over kernel IPC) that wishes to attach to that window
3. Process B, after receiving above mentioned file descriptor from process A over IPC, shall call rte_idxd_window_attach() and receive an inter-pasid handle
4. Process B shall use this handle as an argument for inter-domain operations using DMA device API

drivers/dma/idxd/version.map line 10

Quoted 8 lines

drivers/dma/idxd/version.map new file +8 -0

+};
+
+
+EXPERIMENTAL {
+       global:
+
+       rte_idxd_window_create;
+       rte_idxd_window_attach;

PMD specific API starts with rte_pmd_

Quoted 5 lines

+};
--
2.37.2

-----Original Message-----
From: Anatoly Burakov <[email protected]>
Sent: Friday, August 11, 2023 9:15 AM
To: [email protected]
Cc: [email protected]
Subject: [EXT] [PATCH v1 0/3] Add support for inter-domain DMA operations

External Email

----------------------------------------------------------------------
This patchset adds inter-domain DMA operations, and implements driver support
for them in Intel(R) IDXD driver.

Inter-domain DMA operations are similar to regular DMA operations, except that
source and/or destination addresses will be in virtual address space of another
process. In this patchset, DMA device is extended to support two new data plane
operations: inter-domain copy, and inter-domain fill. No control plane API is
provided for dmadev to set up inter-domain communication (see below for more
info).

-----Original Message-----
From: Anatoly Burakov <[email protected]>
Sent: Friday, August 11, 2023 9:45 PM
To: [email protected]; Chengwen Feng <[email protected]>; Kevin Laatz <[email protected]>; Bruce Richardson <[email protected]>
Cc: Vladimir Medvedkin <[email protected]>
Subject: [EXT] [PATCH v1 1/3] dmadev: add inter-domain operations

External Email

----------------------------------------------------------------------
Add a flag to indicate that a specific device supports inter-domain operations, and add an API for inter-domain copy and fill.

Inter-domain operation is an operation that is very similar to regular DMA operation, except either source or destination addresses can be in a different process's address space, indicated by source and destination handle values. These values are currently meant to be provided by private drivers' API's.

This commit also adds a controller ID field into the DMA device API. This is an arbitrary value that may not be implemented by hardware, but it is meant to represent some kind of device hierarchy.

Signed-off-by Vladimir Medvedkin <[email protected]>

Signed-off-by Anatoly Burakov <[email protected]>

---
 doc/guides/prog_guide/dmadev.rst |  18 +++++
 lib/dmadev/rte_dmadev.c          |   2 +
 lib/dmadev/rte_dmadev.h          | 133
+++++++++++++++++++++++++++++++
 lib/dmadev/rte_dmadev_core.h     |  12 +++
 4 files changed, 165 insertions(+)

(quoted diff) +17 -0

+/**
+ * @warning
+ * @b EXPERIMENTAL: this API may change without prior notice.
+ *
+ * Enqueue an inter-domain copy operation.
+ *
+ * This queues up an inter-domain copy operation to be performed by
+hardware, if
+ * the 'flags' parameter contains RTE_DMA_OP_FLAG_SUBMIT then trigger
+doorbell
+ * to begin this operation, otherwise do not trigger doorbell.
+ *
+ * The source and destination handle parameters are arbitrary opaque
+values,
+ * currently meant to be provided by private device driver API's. If
+the source
+ * handle value is meaningful, RTE_DMA_OP_FLAG_SRC_HANDLE flag must

be set.
+ * Similarly, if the destination handle value is meaningful,
+ * RTE_DMA_OP_FLAG_DST_HANDLE flag must be set. Source and destination

lib/dmadev/rte_dmadev.h +20 -0

+handle
+ * values are meant to provide information to the hardware about source
+and/or
+ * destination PASID for the inter-domain copy operation.
+ *
+ * @param dev_id
+ *   The identifier of the device.
+ * @param vchan
+ *   The identifier of virtual DMA channel.
+ * @param src
+ *   The address of the source buffer (if `src_handle` is set, source address
+ *   will be in address space of process referred to by source handle).
+ * @param dst
+ *   The address of the destination buffer (if `dst_handle` is set, destination
+ *   address will be in address space of process referred to by destination
+ *   handle).
+ * @param length
+ *   The length of the data to be copied.
+ * @param src_handle
+ *   Source handle value (if used, RTE_DMA_OP_FLAG_SRC_HANDLE flag

must be set).
+ * @param dst_handle
+ * Destination handle value (if used, RTE_DMA_OP_FLAG_DST_HANDLE
flag must be
+ * set).
+ * @param flags
+ * Flags for this operation.
+ * @return

+ *   - 0..UINT16_MAX: index of enqueued job.
+ *   - -ENOSPC: if no space left to enqueue.
+ *   - other values < 0 on failure.

+ */

Add a flag to indicate that a specific device supports inter-domain operations, and add an API for inter-domain copy and fill.

Inter-domain operation is an operation that is very similar to regular DMA operation, except either source or destination addresses can be in a different process's address space, indicated by source and destination handle values. These values are currently meant to be provided by private drivers' API's.

This commit also adds a controller ID field into the DMA device API. This is an arbitrary value that may not be implemented by hardware, but it is meant to represent some kind of device hierarchy.

Signed-off-by Vladimir Medvedkin <[email protected]>

Signed-off-by Anatoly Burakov <[email protected]>

---

Hi Anatoly,

Quoted 16 lines · Anatoly Burakov

Add a flag to indicate that a specific device supports inter-domain operations, and add an API for inter-domain copy and fill.

Inter-domain operation is an operation that is very similar to regular DMA operation, except either source or destination addresses can be in a different process's address space, indicated by source and destination handle values. These values are currently meant to be provided by private drivers' API's.

This commit also adds a controller ID field into the DMA device API. This is an arbitrary value that may not be implemented by hardware, but it is meant to represent some kind of device hierarchy.

Signed-off-by Vladimir Medvedkin <[email protected]>

Signed-off-by Anatoly Burakov <[email protected]>

---

...

lib/dmadev/rte_dmadev.h rte_dma_burst_capacity(int16_t dev_id, uint16_t vchan) · line 1205

Quoted 5 lines

lib/dmadev/rte_dmadev.h +5 -0

+__rte_experimental
+static inline int
+rte_dma_copy_inter_dom(int16_t dev_id, uint16_t vchan, rte_iova_t src,
+             rte_iova_t dst, uint32_t length, uint16_t src_handle,
+             uint16_t dst_handle, uint64_t flags)

I would suggest add more general extension:
rte_dma_copy*(int16_t dev_id, uint16_t vchan, rte_iova_t src, rte_iova_t dst,
uint32_t length, uint64_t flags, void *param)
The param only valid under some flags bits.
As for this inter-domain extension: we could define inter-domain param struct.

Whether add in current rte_dma_copy() API or add one new API, I think it mainly depend on performance impact of parameter transfer. Suggest more discuss for differnt platform and call specification.

And last, Could you introduce the application scenarios of this feature?

Thanks.

Hi Satananda, Anoob, Chengwen, Jerin, all,

After a number of internal discussions we have decided that we're going to postpone this feature/patchset till next release.

Quoted 1 line

[Satananda] Have you considered extending rte_dma_port_param and

rte_dma_vchan_conf to represent interdomain memory transfer setup as a separate port type like RTE_DMA_PORT_INTER_DOMAIN ?

Quoted 1 line

[Anoob] Can we move this 'src_handle' and 'dst_handle' registration to

rte_dma_vchan_setup so that the 'src_handle' and 'dst_handle' can be configured in control path and the existing datapath APIs can work as is.

Quoted 1 line

[Jerin] Or move src_handle/dst_hanel to vchan config

We've listened to feedback on implementation, and have prototyped a vchan-based interface. This has a number of advantages and disadvantages, both in terms of API usage and in terms of our specific driver.

Setting up inter-domain operations as separate vchans allow us to store data inside the PMD and not duplicate any API paths, so having multiple vchans addresses that problem. However, this also means that any new vchans added while the PMD is active (such as attaching to a new

process) will have to be gated by start/stop. This is probably fine from API point of view, but a hassle for user (previously, we could've just started using the new inter-domain handle right away).

Another usability issue with multiple vchan approach is that now, each vchan will have its own enqueue/submit/completion cycle, so any use case relying on one thread communicating with many processes will have to process each vchan separately, instead of everything going into one vchan - again, looks fine API-wise, but a hassle for the user, since this requires calling submit and completion for each vchan, and in some cases it requires maintaining some kind of reordering queue. (On the other hand, it would be much easier to separate operations intended for different processes with this approach, so perhaps this is not such a big issue)