On Fri, Jan 31, 2014 at 08:17:58AM +0800, Ming Lei wrote: > On Fri, Jan 31, 2014 at 6:15 AM, Sarah Sharp > <sarah.a.sharp@xxxxxxxxxxxxxxx> wrote: > > On Thu, Jan 30, 2014 at 10:50:21PM +0100, Bjørn Mork wrote: > >> FWIW, the plan looks fine to me. Just adding a couple of hints to > >> simplify the implementation. > >> > >> Sarah Sharp <sarah.a.sharp@xxxxxxxxxxxxxxx> writes: > >> > >> > Let's do this fix the right way, instead of wall papering over the > >> > issue. Here's what we should do: > >> > > >> > 1. Disable scatter-gather for the ax88179_178a driver when it's under an > >> > xHCI host. > >> > >> No need to make this conditional. SG is only enabled in the > >> ax88179_178a driver if udev->bus->no_sg_constraint is true, so it > >> applies only to xHCI hosts in the first place. > > > > Ah, so you're suggesting just reverting commit > > 3804fad45411b48233b48003e33a78f290d227c8 "USBNET: ax88179_178a: enable > > tso if usb host supports sg dma"? > > If I understand the problem correctly, the current issue is that xhci driver > doesn't support the arbitrary dma length not well, but per XHCI spec, it > should be supported, right? > > If the above is correct, reverting the commit isn't correct since there isn't > any issue about the commit, so I suggest to disable the flag in xhci > for the buggy devices, and it may be enabled again if the problem is fixed. Ok, I like that plan, since it means I don't have to touch any networking code to fix this. :) I believe that means we'll have to disable the flag for all 1.0 xHCI hosts, since those are the ones that need TD fragments. > >> > 2. Revert the following commits: > >> > f2d9b991c549 xhci: Set scatter-gather limit to avoid failed block writes. > >> > d6c9ea9069af xhci: Avoid infinite loop when sg urb requires too many trbs > >> > 35773dac5f86 usb: xhci: Link TRB must not occur within a USB payload burst > >> > > >> > 3. Dan and Mathias can work together to come up with an overall plan to > >> > change the xHCI driver architecture to be fully compliant with the TD > >> > fragment rules. That can be done over the next few kernel releases. > >> > > >> > The end result is that we don't destabilize storage or break userspace > >> > USB drivers, we don't break people's xHCI host controllers, > >> > the ax88179_178a USB ethernet devices still work under xHCI (a bit with > >> > worse performance), and other USB ethernet devices still get the > >> > performance improvement introduced in 3.12. > >> > >> No other usbnet drivers has enabled SG... Which is why you have only > >> seen this problem with the ax88179_178a devices. So there is no > >> performance improvement to keep. > > In my test environment, the patch does improve both throughput and > cpu utilization, if you search the previous email for the patch, you can > see the data. Right, I did see the performance improvement note in that commit. Do you know if the ARM A15 dual core board was using a 0.96 xHCI host, or a 1.0 host? You can find out by reloading the xHCI driver with dynamic debugging turned on: # sudo modprobe xhci_hcd dyndbg and then look for lines like: [25296.765767] xhci_hcd 0000:00:14.0: HCIVERSION: 0x100 Sarah Sharp -- To unsubscribe from this list: send the line "unsubscribe linux-usb" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
