On 2025-06-30 19:34, Pathak, Pravin wrote:
-----Original Message-----
From: Mattias Rönnblom <hof...@lysator.liu.se>
Sent: Monday, June 30, 2025 12:51 PM
To: Pathak, Pravin <pravin.pat...@intel.com>; Jerin Jacob
<jerinjac...@gmail.com>
Cc: dev@dpdk.org; jer...@marvell.com; Chen, Mike Ximing
<mike.ximing.c...@intel.com>; Richardson, Bruce
<bruce.richard...@intel.com>; tho...@monjalon.net; Marchand, David
<david.march...@redhat.com>; nipun.gu...@amd.com;
chen...@nvidia.com; Sarkar, Tirthendu <tirthendu.sar...@intel.com>; Pavan
Nikhilesh <pbhagavat...@marvell.com>; Shijith Thotton
<sthot...@marvell.com>; Hemant Agrawal <hemant.agra...@nxp.com>;
Sachin Saxena <sachin.sax...@oss.nxp.com>; harry.ch...@intel.com;
Mattias Rönnblom <mattias.ronnb...@ericsson.com>
Subject: Re: [PATCH v1] event/dlb2: add dequeue interrupt mode support
On 2025-06-30 18:18, Pathak, Pravin wrote:
-----Original Message-----
From: Jerin Jacob <jerinjac...@gmail.com>
Sent: Monday, June 30, 2025 7:44 AM
To: Mattias Rönnblom <hof...@lysator.liu.se>
Cc: Pathak, Pravin <pravin.pat...@intel.com>; dev@dpdk.org;
jer...@marvell.com; Chen, Mike Ximing <mike.ximing.c...@intel.com>;
Richardson, Bruce <bruce.richard...@intel.com>; tho...@monjalon.net;
Marchand, David <david.march...@redhat.com>;
nipun.gu...@amd.com;
chen...@nvidia.com; Sarkar, Tirthendu <tirthendu.sar...@intel.com>;
Pavan Nikhilesh <pbhagavat...@marvell.com>; Shijith Thotton
<sthot...@marvell.com>; Hemant Agrawal <hemant.agra...@nxp.com>;
Sachin Saxena <sachin.sax...@oss.nxp.com>; harry.ch...@intel.com;
Mattias Rönnblom <mattias.ronnb...@ericsson.com>
Subject: Re: [PATCH v1] event/dlb2: add dequeue interrupt mode
support
On Mon, Jun 30, 2025 at 4:47 PM Mattias Rönnblom
<hof...@lysator.liu.se>
wrote:
On 2025-06-30 11:19, Jerin Jacob wrote:
On Sat, Jun 28, 2025 at 11:17 AM Pravin Pathak
<pravin.pat...@intel.com> wrote:
DLB2 port interrupt is implemented using DPDK interrupt framework.
This allows eventdev dequeue API to sleep when the port queue is
empty and gets wakeup when event arrives at the port. Port dequeue
mode is configured using devargs argument port_dequeue_wait.
Supported modes are polling and interrupt. Default mode is polling.
This commit also adds code to handle device error interrupts and
print alarm details.
Signed-off-by: Pravin Pathak <pravin.pat...@intel.com>
Signed-off-by: Tirthendu Sarkar <tirthendu.sar...@intel.com>
---
doc/guides/eventdevs/dlb2.rst | 20 +
drivers/event/dlb2/dlb2.c | 236 +++++-
drivers/event/dlb2/dlb2_iface.c | 7 +
drivers/event/dlb2/dlb2_iface.h | 8 +
drivers/event/dlb2/dlb2_priv.h | 18 +
drivers/event/dlb2/dlb2_user.h | 112 +++
drivers/event/dlb2/pf/base/dlb2_hw_types.h | 70 ++
drivers/event/dlb2/pf/base/dlb2_osdep.h | 46 ++
drivers/event/dlb2/pf/base/dlb2_regs.h | 149 +++-
drivers/event/dlb2/pf/base/dlb2_resource.c | 825
+++++++++++++++++++++
drivers/event/dlb2/pf/base/dlb2_resource.h | 6 +
drivers/event/dlb2/pf/dlb2_pf.c | 223 ++++++
12 files changed, 1711 insertions(+), 9 deletions(-)
diff --git a/doc/guides/eventdevs/dlb2.rst
b/doc/guides/eventdevs/dlb2.rst index 8ec7168f20..a4ba857351
100644
--- a/doc/guides/eventdevs/dlb2.rst
+++ b/doc/guides/eventdevs/dlb2.rst
@@ -477,6 +477,26 @@ Example command to use as meson option
for
credit handling:
meson configure -Dc_args='-DDLB_SW_CREDITS_CHECKS=0 -
DDLB_HW_CREDITS_CHECKS=1'
+Interrupt Mode Support
+~~~~~~~~~~~~~~~~~~~~~~
+DLB dequeue supports interrupt mode for the API
rte_event_dequeue_burst().
+The default port dequeue mode is polling. Dequeue wait mode can
+be configured on per eventdev port basis using devargs argument
+'port_dequeue_wait'. In interrupt mode, if the port queue is
+empty, the application thread will block on the interrupt until a
+new event arrives. It enters blocking mode only after any
+specified timeout. During the timeout, it will poll the port
+queue for
events as usual. Interrupt mode uses the DPDK interrupt support
framework.
+
+ .. code-block:: console
+
+ --allow ea:00.0,port_dequeue_wait=all:interrupt
Adding other eventdev PMD mainatainers.
Looks like it can be a generic feature. i.e set this option is
dev_configure() If there is no objection, Please send a new patch
around
that.
I've considered implementing this in DSW, although in a different
manner (with eventfds and poll()).
The dequeue timeout will still be honored in "interrupt mode", correct?
It wasn't obvious from the description.
How is it in Intel PMD?
It would be best if we configure it per port using RTE_EVENT_PORT_CFG_*
flags. Will it be, OK?
The dequeue timeout will be honored, and the decision to block or return
will be made after the timeout.
That doesn't sound like the timeout is honored.
The reason an application wants the dequeue call to complete within a certain
time, even though there wasn't any events, is likely because it want to go do
something else with that thread, after the timeout.
Thus, you can't decide to block the thread *after* the timeout. If you block,
you have to do some time *before* the timeout, and wake up in time to meet
the deadline.
For example, if the event device is given a 1 ms dequeue timeout by the
application, it could go busy-poll for 10 us, then busy-poll with a short tpause
for 100 us, and then put the thread to sleep blocking on some fd for the
remaining 890 us.
The hardware-specific nature of the timing and exact mechanism to use
speaks against having this kind of configuration in the Eventdev API.
The mode is not for what to do during a timeout, but after a timeout.
My comments were not so much concerning any DLB-specific extension, but
rather how this kind of function should work, if it was a part of the
standard API.
We can enter sleep mode immediately by setting the timeout to 0 if we need to.
This mode is not changing the current timeout behavior. After the timeout,
it allows HW devices supporting interrupts to block on an interrupt.
The current API specifies that control is returned to the application,
after the timeout has expired. If you change that with a PMD parameter,
the DLB behavior will be in violation of the API contract. Applications
using rte_keepalive_alive() between dequeues is one example of those
that will break. In fact, all applications that use more than one RTE
service will break.
It will wake up only after a new event arrives at the port. If the application
needs control
back then it can use the current default non-blocking mode. A better mode to
save power during timeout
will be to use umwait-based sleep. Consider this as extension to current
timeout behavior if device
supports interrupts.
What about applications that both want power efficiency *and* require a
timeout?
It makes no sense to me the change the semantics of the dequeue timeout
parameter from "the time until I want control back" to "the time I want
the event device to use polling, after which it should put the thread to
sleep". Those two are pretty much orthogonal.
The current API doesn't specify what happens during the timeout. If you
by "non-blocking" mean "busy-polling", that is not an API requirement. I
don't see why the event device couldn't put the lcore thread to sleep
during a long timeout (and I also see why you may not want that to be
the default behavior).
If not interrupt, it can be called blocking vs polling mode. If the port
config is
fine, I will create a new patch with it.
Also, we should have this as a capability for eventdevs.
What's being configured should just be a threshold time at which the
event device would go from busy-polling to blocking the thread.
Maybe it should be called something with "blocking" or "sleeping",
instead of "interrupt", since interrupts are never directly involved.
Agree. or make it a power save mode or so.
Anyway, seems like a good candidate for a generic feature to me.
