From cc62a7eb6396e8be95b9a30053ed09191818b99b Mon Sep 17 00:00:00 2001 From: Kirill Smelkov Date: Sun, 3 Jul 2011 20:36:57 +0400 Subject: USB: EHCI: Allow users to override 80% max periodic bandwidth There are cases, when 80% max isochronous bandwidth is too limiting. For example I have two USB video capture cards which stream uncompressed video, and to stream full NTSC + PAL videos we'd need NTSC 640x480 YUV422 @30fps ~17.6 MB/s PAL 720x576 YUV422 @25fps ~19.7 MB/s isoc bandwidth. Now, due to limited alt settings in capture devices NTSC one ends up streaming with max_pkt_size=2688 and PAL with max_pkt_size=2892, both with interval=1. In terms of microframe time allocation this gives NTSC ~53us PAL ~57us and together ~110us > 100us == 80% of 125us uframe time. So those two devices can't work together simultaneously because the'd over allocate isochronous bandwidth. 80% seemed a bit arbitrary to me, and I've tried to raise it to 90% and both devices started to work together, so I though sometimes it would be a good idea for users to override hardcoded default of max 80% isoc bandwidth. After all, isn't it a user who should decide how to load the bus? If I can live with 10% or even 5% bulk bandwidth that should be ok. I'm a USB newcomer, but that 80% set in stone by USB 2.0 specification seems to be chosen pretty arbitrary to me, just to serve as a reasonable default. NOTE 1 ~~~~~~ for two streams with max_pkt_size=3072 (worst case) both time allocation would be 60us+60us=120us which is 96% periodic bandwidth leaving 4% for bulk and control. Alan Stern suggested that bulk then would be problematic (less than 300*8 bittimes left per microframe), but I think that is still enough for control traffic. NOTE 2 ~~~~~~ Sarah Sharp expressed concern that maxing out periodic bandwidth could lead to vendor-specific hardware bugs on host controllers, because > It's entirely possible that you'll run into > vendor-specific bugs if you try to pack the schedule with isochronous > transfers. I don't think any hardware designer would seriously test or > validate their hardware with a schedule that is basically a violation of > the USB bus spec (more than 80% for periodic transfers). So far I've only tested this patch on my HP Mini 5103 with N10 chipset kirr@mini:~$ lspci 00:00.0 Host bridge: Intel Corporation N10 Family DMI Bridge 00:02.0 VGA compatible controller: Intel Corporation N10 Family Integrated Graphics Controller 00:02.1 Display controller: Intel Corporation N10 Family Integrated Graphics Controller 00:1b.0 Audio device: Intel Corporation N10/ICH 7 Family High Definition Audio Controller (rev 02) 00:1c.0 PCI bridge: Intel Corporation N10/ICH 7 Family PCI Express Port 1 (rev 02) 00:1c.3 PCI bridge: Intel Corporation N10/ICH 7 Family PCI Express Port 4 (rev 02) 00:1d.0 USB Controller: Intel Corporation N10/ICH 7 Family USB UHCI Controller #1 (rev 02) 00:1d.1 USB Controller: Intel Corporation N10/ICH 7 Family USB UHCI Controller #2 (rev 02) 00:1d.2 USB Controller: Intel Corporation N10/ICH 7 Family USB UHCI Controller #3 (rev 02) 00:1d.3 USB Controller: Intel Corporation N10/ICH 7 Family USB UHCI Controller #4 (rev 02) 00:1d.7 USB Controller: Intel Corporation N10/ICH 7 Family USB2 EHCI Controller (rev 02) 00:1e.0 PCI bridge: Intel Corporation 82801 Mobile PCI Bridge (rev e2) 00:1f.0 ISA bridge: Intel Corporation NM10 Family LPC Controller (rev 02) 00:1f.2 SATA controller: Intel Corporation N10/ICH7 Family SATA AHCI Controller (rev 02) 01:00.0 Network controller: Broadcom Corporation BCM4313 802.11b/g/n Wireless LAN Controller (rev 01) 02:00.0 Ethernet controller: Marvell Technology Group Ltd. 88E8059 PCI-E Gigabit Ethernet Controller (rev 11) and the system works stable with 110us/uframe (~88%) isoc bandwith allocated for above-mentioned isochronous transfers. NOTE 3 ~~~~~~ This feature is off by default. I mean max periodic bandwidth is set to 100us/uframe by default exactly as it was before the patch. So only those of us who need the extreme settings are taking the risk - normal users who do not alter uframe_periodic_max sysfs attribute should not see any change at all. NOTE 4 ~~~~~~ I've tried to update documentation in Documentation/ABI/ thoroughly, but only "TBD" was put into Documentation/usb/ehci.txt -- the text there seems to be outdated and much needing refreshing, before it could be amended. Cc: Sarah Sharp Signed-off-by: Kirill Smelkov Acked-by: Alan Stern Signed-off-by: Greg Kroah-Hartman --- Documentation/ABI/testing/sysfs-module | 23 +++++++++++++++++++++++ Documentation/usb/ehci.txt | 2 ++ 2 files changed, 25 insertions(+) (limited to 'Documentation') diff --git a/Documentation/ABI/testing/sysfs-module b/Documentation/ABI/testing/sysfs-module index cfcec3bffc0a..9489ea8e294c 100644 --- a/Documentation/ABI/testing/sysfs-module +++ b/Documentation/ABI/testing/sysfs-module @@ -10,3 +10,26 @@ KernelVersion: 2.6.35 Contact: masa-korg@dsn.okisemi.com Description: Write/read Option ROM data. + +What: /sys/module/ehci_hcd/drivers/.../uframe_periodic_max +Date: July 2011 +KernelVersion: 3.1 +Contact: Kirill Smelkov +Description: Maximum time allowed for periodic transfers per microframe (μs) + + [ USB 2.0 sets maximum allowed time for periodic transfers per + microframe to be 80%, that is 100 microseconds out of 125 + microseconds (full microframe). + + However there are cases, when 80% max isochronous bandwidth is + too limiting. For example two video streams could require 110 + microseconds of isochronous bandwidth per microframe to work + together. ] + + Through this setting it is possible to raise the limit so that + the host controller would allow allocating more than 100 + microseconds of periodic bandwidth per microframe. + + Beware, non-standard modes are usually not thoroughly tested by + hardware designers, and the hardware can malfunction when this + setting differ from default 100. diff --git a/Documentation/usb/ehci.txt b/Documentation/usb/ehci.txt index 9dcafa7d930d..160bd6c3ab7b 100644 --- a/Documentation/usb/ehci.txt +++ b/Documentation/usb/ehci.txt @@ -210,3 +210,5 @@ TBD: Interrupt and ISO transfer performance issues. Those periodic transfers are fully scheduled, so the main issue is likely to be how to trigger "high bandwidth" modes. +TBD: More than standard 80% periodic bandwidth allocation is possible +through sysfs uframe_periodic_max parameter. Describe that. -- cgit v1.2.3