On Fri, Jun 11, 2021 at 04:00:38PM +0300, Felipe Balbi wrote: > > Hi, > > Wesley Cheng <wcheng@xxxxxxxxxxxxxx> writes: > >>>>>>> to be honest, I don't think these should go in (apart from the build > >>>>>>> failure) because it's likely to break instantiations of the core with > >>>>>>> differing FIFO sizes. Some instantiations even have some endpoints with > >>>>>>> dedicated functionality that requires the default FIFO size configured > >>>>>>> during coreConsultant instantiation. I know of at OMAP5 and some Intel > >>>>>>> implementations which have dedicated endpoints for processor tracing. > >>>>>>> > >>>>>>> With OMAP5, these endpoints are configured at the top of the available > >>>>>>> endpoints, which means that if a gadget driver gets loaded and takes > >>>>>>> over most of the FIFO space because of this resizing, processor tracing > >>>>>>> will have a hard time running. That being said, processor tracing isn't > >>>>>>> supported in upstream at this moment. > >>>>>>> > >>>>> > >>>>> I agree that the application of this logic may differ between vendors, > >>>>> hence why I wanted to keep this controllable by the DT property, so that > >>>>> for those which do not support this use case can leave it disabled. The > >>>>> logic is there to ensure that for a given USB configuration, for each EP > >>>>> it would have at least 1 TX FIFO. For USB configurations which don't > >>>>> utilize all available IN EPs, it would allow re-allocation of internal > >>>>> memory to EPs which will actually be in use. > >>>> > >>>> The feature ends up being all-or-nothing, then :-) It sounds like we can > >>>> be a little nicer in this regard. > >>>> > >>> > >>> Don't get me wrong, I think once those features become available > >>> upstream, we can improve the logic. From what I remember when looking > >> > >> sure, I support that. But I want to make sure the first cut isn't likely > >> to break things left and right :) > >> > >> Hence, let's at least get more testing. > >> > > > > Sure, I'd hope that the other users of DWC3 will also see some pretty > > big improvements on the TX path with this. > > fingers crossed > > >>> at Andy Shevchenko's Github, the Intel tracer downstream changes were > >>> just to remove physical EP1 and 2 from the DWC3 endpoint list. If that > >> > >> right, that's the reason why we introduced the endpoint feature > >> flags. The end goal was that the UDC would be able to have custom > >> feature flags paired with ->validate_endpoint() or whatever before > >> allowing it to be enabled. Then the UDC driver could tell UDC core to > >> skip that endpoint on that particular platform without interefering with > >> everything else. > >> > >> Of course, we still need to figure out a way to abstract the different > >> dwc3 instantiations. > >> > >>> was the change which ended up upstream for the Intel tracer then we > >>> could improve the logic to avoid re-sizing those particular EPs. > >> > >> The problem then, just as I mentioned in the previous paragraph, will be > >> coming up with a solution that's elegant and works for all different > >> instantiations of dwc3 (or musb, cdns3, etc). > >> > > > > Well, at least for the TX FIFO resizing logic, we'd only be needing to > > focus on the DWC3 implementation. > > > > You bring up another good topic that I'll eventually needing to be > > taking a look at, which is a nice way we can handle vendor specific > > endpoints and how they can co-exist with other "normal" endpoints. We > > have a few special HW eps as well, which we try to maintain separately > > in our DWC3 vendor driver, but it isn't the most convenient, or most > > pretty method :). > > Awesome, as mentioned, the endpoint feature flags were added exactly to > allow for these vendor-specific features :-) > > I'm more than happy to help testing now that I finally got our SM8150 > Surface Duo device tree accepted by Bjorn ;-) > > >>> However, I'm not sure how the changes would look like in the end, so I > >>> would like to wait later down the line to include that :). > >> > >> Fair enough, I agree. Can we get some more testing of $subject, though? > >> Did you test $subject with upstream too? Which gadget drivers did you > >> use? How did you test > >> > > > > The results that I included in the cover page was tested with the pure > > upstream kernel on our device. Below was using the ConfigFS gadget w/ a > > mass storage only composition. > > > > Test Parameters: > > - Platform: Qualcomm SM8150 > > - bMaxBurst = 6 > > - USB req size = 256kB > > - Num of USB reqs = 16 > > do you mind testing with the regular request size (16KiB) and 250 > requests? I think we can even do 15 bursts in that case. > > > - USB Speed = Super-Speed > > - Function Driver: Mass Storage (w/ ramdisk) > > - Test Application: CrystalDiskMark > > > > Results: > > > > TXFIFO Depth = 3 max packets > > > > Test Case | Data Size | AVG tput (in MB/s) > > ------------------------------------------- > > Sequential|1 GB x | > > Read |9 loops | 193.60 > > | | 195.86 > > | | 184.77 > > | | 193.60 > > ------------------------------------------- > > > > TXFIFO Depth = 6 max packets > > > > Test Case | Data Size | AVG tput (in MB/s) > > ------------------------------------------- > > Sequential|1 GB x | > > Read |9 loops | 287.35 > > | | 304.94 > > | | 289.64 > > | | 293.61 > > I remember getting close to 400MiB/sec with Intel platforms without > resizing FIFOs and I'm sure the FIFO size was set to 2x1024, though my > memory could be failing. > > Then again, I never ran with CrystalDiskMark, I was using my own tool > (it's somewhere in github. If you care, I can look up the URL). > > > We also have internal numbers which have shown similar improvements as > > well. Those are over networking/tethering interfaces, so testing IPERF > > loopback over TCP/UDP. > > loopback iperf? That would skip the wire, no? > > >>> size of 2 and TX threshold of 1, this would really be not beneficial to > >>> us, because we can only change the TX threshold to 2 at max, and at > >>> least in my observations, once we have to go out to system memory to > >>> fetch the next data packet, that latency takes enough time for the > >>> controller to end the current burst. > >> > >> What I noticed with g_mass_storage is that we can amortize the cost of > >> fetching data from memory, with a deeper request queue. Whenever I > >> test(ed) g_mass_storage, I was doing so with 250 requests. And that was > >> enough to give me very good performance. Never had to poke at TX FIFO > >> resizing. Did you try something like this too? > >> > >> I feel that allocating more requests is a far simpler and more generic > >> method that changing FIFO sizes :) > >> > > > > I wish I had a USB bus trace handy to show you, which would make it very > > clear how the USB bus is currently utilized with TXFIFO size 2 vs 6. So > > by increasing the number of USB requests, that will help if there was a > > bottleneck at the SW level where the application/function driver > > utilizing the DWC3 was submitting data much faster than the HW was > > processing them. > > > > So yes, this method of increasing the # of USB reqs will definitely help > > with situations such as HSUSB or in SSUSB when EP bursting isn't used. > > The TXFIFO resize comes into play for SSUSB, which utilizes endpoint > > bursting. > > Hmm, that's not what I remember. Perhaps the TRB cache size plays a role > here too. I have clear memories of testing this very scenario of > bursting (using g_mass_storage at the time) because I was curious about > it. Back then, my tests showed no difference in behavior. > > It could be nice if Heikki could test Intel parts with and without your > changes on g_mass_storage with 250 requests. Andy, you have a system at hand that has the DWC3 block enabled, right? Can you help out here? thanks, > > Now with endpoint bursting, if the function notifies the host that > > bursting is supported, when the host sends the ACK for the Data Packet, > > it should have a NumP value equal to the bMaxBurst reported in the EP > > Yes and no. Looking back at the history, we used to configure NUMP based > on bMaxBurst, but it was changed later in commit > 4e99472bc10bda9906526d725ff6d5f27b4ddca1 by yours truly because of a > problem reported by John Youn. > > And now we've come full circle. Because even if I believe more requests > are enough for bursting, NUMP is limited by the RxFIFO size. This ends > up supporting your claim that we need RxFIFO resizing if we want to > squeeze more throughput out of the controller. > > However, note that this is about RxFIFO size, not TxFIFO size. In fact, > looking at Table 8-13 of USB 3.1 r1.0, we read the following about NumP > (emphasis is mine): > > "Number of Packets (NumP). This field is used to indicate the > number of Data Packet buffers that the **receiver** can > accept. The value in this field shall be less than or equal to > the maximum burst size supported by the endpoint as determined > by the value in the bMaxBurst field in the Endpoint Companion > Descriptor (refer to Section 9.6.7)." > > So, NumP is for the receiver, not the transmitter. Could you clarify > what you mean here? > > /me keeps reading > > Hmm, table 8-15 tries to clarify: > > "Number of Packets (NumP). > > For an OUT endpoint, refer to Table 8-13 for the description of > this field. > > For an IN endpoint this field is set by the endpoint to the > number of packets it can transmit when the host resumes > transactions to it. This field shall not have a value greater > than the maximum burst size supported by the endpoint as > indicated by the value in the bMaxBurst field in the Endpoint > Companion Descriptor. Note that the value reported in this field > may be treated by the host as informative only." > > However, if I remember correctly (please verify dwc3 databook), NUMP in > DCFG was only for receive buffers. Thin, John, how does dwc3 compute > NumP for TX/IN endpoints? Is that computed as a function of DCFG.NUMP or > TxFIFO size? > > > desc. If we have a TXFIFO size of 2, then normally what I have seen is > > that after 2 data packets, the device issues a NRDY. So then we'd need > > to send an ERDY once data is available within the FIFO, and the same > > sequence happens until the USB request is complete. With this constant > > NRDY/ERDY handshake going on, you actually see that the bus is under > > utilized. When we increase an EP's FIFO size, then you'll see constant > > bursts for a request, until the request is done, or if the host runs out > > of RXFIFO. (ie no interruption [on the USB protocol level] during USB > > request data transfer) > > Unfortunately I don't have access to a USB sniffer anymore :-( > > >>>>>> Good points. > >>>>>> > >>>>>> Wesley, what kind of testing have you done on this on different devices? > >>>>>> > >>>>> > >>>>> As mentioned above, these changes are currently present on end user > >>>>> devices for the past few years, so its been through a lot of testing :). > >>>> > >>>> all with the same gadget driver. Also, who uses USB on android devices > >>>> these days? Most of the data transfer goes via WiFi or Bluetooth, anyway > >>>> :-) > >>>> > >>>> I guess only developers are using USB during development to flash dev > >>>> images heh. > >>>> > >>> > >>> I used to be a customer facing engineer, so honestly I did see some > >>> really interesting and crazy designs. Again, we do have non-Android > >>> products that use the same code, and it has been working in there for a > >>> few years as well. The TXFIFO sizing really has helped with multimedia > >>> use cases, which use isoc endpoints, since esp. in those lower end CPU > >>> chips where latencies across the system are much larger, and a missed > >>> ISOC interval leads to a pop in your ear. > >> > >> This is good background information. Thanks for bringing this > >> up. Admitedly, we still have ISOC issues with dwc3. I'm interested in > >> knowing if a deeper request queue would also help here. > >> > >> Remember dwc3 can accomodate 255 requests + link for each endpoint. If > >> our gadget driver uses a low number of requests, we're never really > >> using the TRB ring in our benefit. > >> > > > > We're actually using both a deeper USB request queue + TX fifo resizing. :). > > okay, great. Let's see what John and/or Thinh respond WRT dwc3 TX Burst > behavior. -- heikki
