> -----Original Message----- > From: Mattias Rönnblom <hof...@lysator.liu.se> > Sent: Thursday, July 3, 2025 5:25 AM > 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 2025-07-01 23:08, Pathak, Pravin wrote: > > > > > >> -----Original Message----- > >> From: Mattias Rönnblom <hof...@lysator.liu.se> > >> Sent: Tuesday, July 1, 2025 4:16 AM > >> 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 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). > > > > I got your point. Application will prefer to return and not block > > after the timeout as per current API description. Current API > > signature is = 0 no-wait, returns immediately if there is no event. > >> 0 wait for the event or timeout > > Will it be OK to extend it to treat max timeout 0xffffffff as block > > for event with PMD specific Mechanism to wait for the event ? Port specific > configuration will not be required in this case. > > Devices supporting interrupts then can use interrupt blocking mode > internally. > > > > Correct me if I'm wrong here, but I think an event device is free to block > using > a PMD-specific mechanism with any non-zero timeout. The longer the > timeout, the more sense it make to put the thread to sleep (blocking on an > fd). > > I also think that the details of how to spend the timeout time probably needs > to be configured by the app (at startup). Different modes, thresholds, etc. > Maybe such are best off as PMD parameters at this point. > > Is there some limitation in the interrupt APIs, or what is preventing the DLB > driver to both honor a finite timeout and block/put the lcore thread to sleep?
Current API definition does not specify or put restriction on timeout mechanism PMD decides to implement. But it will be nice to have application some control on it. DLB PMD supports polling, umwait and interrupt blocking as three modes. Current configuration is devargs based and specific to DLB PMD. If application has choice at each dequeue call, it can decide what mechanism to use. Polling for lower latencies, umwait for power saving and interrupt blocking to make a de-scheduling call and release CPU for other thread. We had implementation supporting these using most significant bits of timeout value on per dequeue call basis. But as it breaks API, now it is done with devargs. If control over dequeue wait is useful to applications, then it can be standardized instead of being PMD specific. Else, we will keep it the way it is now in the patch. I took look at ethdev PMD and there additional APIs are used for blocking. rte_eth_dev_rx_intr_enable epoll_wait() rte_eth_dev_rx_intr_disable And other APIs to configure interrupts. But Eventdev mechanism of doing all inside dequeue API looks Simple. > > >> > >>>> > >>>>> 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. > >>>>>>> > >>> > >
