| Message ID | 1590630363-3934-1-git-send-email-wcheng@codeaurora.org (mailing list archive) |
|---|---|
| Headers | show |
| Series | Re-introduce TX FIFO resize for larger EP bursting | expand |
On Wed, May 27, 2020 at 06:46:00PM -0700, Wesley Cheng wrote: > Changes in V3: > - Removed "Reviewed-by" tags > - Renamed series back to RFC > - Modified logic to ensure that fifo_size is reset if we pass the minimum > threshold. Tested with binding multiple FDs requesting 6 FIFOs. > > Changes in V2: > - Modified TXFIFO resizing logic to ensure that each EP is reserved a > FIFO. > - Removed dev_dbg() prints and fixed typos from patches > - Added some more description on the dt-bindings commit message > > Currently, there is no functionality to allow for resizing the TXFIFOs, and > relying on the HW default setting for the TXFIFO depth. In most cases, the > HW default is probably sufficient, but for USB compositions that contain > multiple functions that require EP bursting, the default settings > might not be enough. Also to note, the current SW will assign an EP to a > function driver w/o checking to see if the TXFIFO size for that particular > EP is large enough. (this is a problem if there are multiple HW defined > values for the TXFIFO size) > > It is mentioned in the SNPS databook that a minimum of TX FIFO depth = 3 > is required for an EP that supports bursting. Otherwise, there may be > frequent occurences of bursts ending. For high bandwidth functions, > such as data tethering (protocols that support data aggregation), mass > storage, and media transfer protocol (over FFS), the bMaxBurst value can be > large, and a bigger TXFIFO depth may prove to be beneficial in terms of USB > throughput. (which can be associated to system access latency, etc...) It > allows for a more consistent burst of traffic, w/o any interruptions, as > data is readily available in the FIFO. > > With testing done using the mass storage function driver, the results show > that with a larger TXFIFO depth, the bandwidth increased significantly. Why is this still a "RFC" series? That implies you don't want this applied...
On 5/29/2020 3:12 AM, Greg KH wrote: > On Wed, May 27, 2020 at 06:46:00PM -0700, Wesley Cheng wrote: >> Changes in V3: >> - Removed "Reviewed-by" tags >> - Renamed series back to RFC >> - Modified logic to ensure that fifo_size is reset if we pass the minimum >> threshold. Tested with binding multiple FDs requesting 6 FIFOs. >> >> Changes in V2: >> - Modified TXFIFO resizing logic to ensure that each EP is reserved a >> FIFO. >> - Removed dev_dbg() prints and fixed typos from patches >> - Added some more description on the dt-bindings commit message >> >> Currently, there is no functionality to allow for resizing the TXFIFOs, and >> relying on the HW default setting for the TXFIFO depth. In most cases, the >> HW default is probably sufficient, but for USB compositions that contain >> multiple functions that require EP bursting, the default settings >> might not be enough. Also to note, the current SW will assign an EP to a >> function driver w/o checking to see if the TXFIFO size for that particular >> EP is large enough. (this is a problem if there are multiple HW defined >> values for the TXFIFO size) >> >> It is mentioned in the SNPS databook that a minimum of TX FIFO depth = 3 >> is required for an EP that supports bursting. Otherwise, there may be >> frequent occurences of bursts ending. For high bandwidth functions, >> such as data tethering (protocols that support data aggregation), mass >> storage, and media transfer protocol (over FFS), the bMaxBurst value can be >> large, and a bigger TXFIFO depth may prove to be beneficial in terms of USB >> throughput. (which can be associated to system access latency, etc...) It >> allows for a more consistent burst of traffic, w/o any interruptions, as >> data is readily available in the FIFO. >> >> With testing done using the mass storage function driver, the results show >> that with a larger TXFIFO depth, the bandwidth increased significantly. > > Why is this still a "RFC" series? That implies you don't want this > applied... > Hi Greg, As Felipe mentioned, we need to make sure that this TX FIFO resize logic is carefully thought out, since the behavior could be different based off the HW configuration as shown in the past. Eventually, I hope that this does get applied, but I think the changes needs more detailed reviews, as there may be potential shortfalls I did not consider due to my limited knowledge of what happened w/ the previous logic. That's pretty much the reason for tagging it as a RFC, since we still need to hash out if this is the right approach. Thanks!
Changes in V3: - Removed "Reviewed-by" tags - Renamed series back to RFC - Modified logic to ensure that fifo_size is reset if we pass the minimum threshold. Tested with binding multiple FDs requesting 6 FIFOs. Changes in V2: - Modified TXFIFO resizing logic to ensure that each EP is reserved a FIFO. - Removed dev_dbg() prints and fixed typos from patches - Added some more description on the dt-bindings commit message Currently, there is no functionality to allow for resizing the TXFIFOs, and relying on the HW default setting for the TXFIFO depth. In most cases, the HW default is probably sufficient, but for USB compositions that contain multiple functions that require EP bursting, the default settings might not be enough. Also to note, the current SW will assign an EP to a function driver w/o checking to see if the TXFIFO size for that particular EP is large enough. (this is a problem if there are multiple HW defined values for the TXFIFO size) It is mentioned in the SNPS databook that a minimum of TX FIFO depth = 3 is required for an EP that supports bursting. Otherwise, there may be frequent occurences of bursts ending. For high bandwidth functions, such as data tethering (protocols that support data aggregation), mass storage, and media transfer protocol (over FFS), the bMaxBurst value can be large, and a bigger TXFIFO depth may prove to be beneficial in terms of USB throughput. (which can be associated to system access latency, etc...) It allows for a more consistent burst of traffic, w/o any interruptions, as data is readily available in the FIFO. With testing done using the mass storage function driver, the results show that with a larger TXFIFO depth, the bandwidth increased significantly. Test Parameters: - Platform: Qualcomm SM8150 - bMaxBurst = 6 - USB req size = 256kB - Num of USB reqs = 16 - 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 ------------------------------------------- Wesley Cheng (3): usb: dwc3: Resize TX FIFOs to meet EP bursting requirements arm64: boot: dts: qcom: sm8150: Enable dynamic TX FIFO resize logic dt-bindings: usb: dwc3: Add entry for tx-fifo-resize Documentation/devicetree/bindings/usb/dwc3.txt | 2 +- arch/arm64/boot/dts/qcom/sm8150.dtsi | 1 + drivers/usb/dwc3/core.c | 2 + drivers/usb/dwc3/core.h | 8 ++ drivers/usb/dwc3/ep0.c | 37 +++++++- drivers/usb/dwc3/gadget.c | 115 +++++++++++++++++++++++++ 6 files changed, 163 insertions(+), 2 deletions(-)