Re: [linux-usb-devel] USB performance bug since kernel 2.6.13 (CRITICAL???)

On Fri, 13 Oct 2006, Open Source wrote:

Hi Wolfgang (and all),

Thanks for the input. However, I am not understanding
exactly why kernel mode is treated any differently than
user mode for this sort of thing. I am looking at the code
in ehci-q.c and ehci-hcd.c.

It seems like the unlinking of completed URBs
happens asynchronously on a timer. This is a
surprise to me since I thought this was happening
on an IRQ from the host controller. But if what I'm
surmising is correct it would explain everything
I am seeing. I'm not able to ascertain how
user mode drivers are treated differently than
kernel mode drivers in this regard. From what I
can tell, all drivers would be broken equally!
Can anyone who has more experience
with this code confirm this for me?

I don't think so. You must be mis-reading the code. The only timers used
in ehci-hcd are a couple of watchdogs; they shouldn't affect the normal
URB completions which occur within ehci_work(), called by ehci_irq().

What Wolfgang meant was that user processes are subject to unpredictable
delays from all kinds of sources.

Alan Stern

-
To unsubscribe from this list: send the line "unsubscribe linux-kernel" in
the body of a message to majordomo@xxxxxxxxxxxxxxx
More majordomo info at http://vger.kernel.org/majordomo-info.html
Please read the FAQ at http://www.tux.org/lkml/

Relevant Pages

  • Re: PCI_COMMON_CONFIG with HalGetBusData in CE-6.0
    ... In general most of the functions that directly access component buses will ... After I switched my driver to kernel mode, ... Halxxx functions work only in kernel mode. ... kernel mode drivers? ...
    (microsoft.public.windowsce.platbuilder)
  • Re: IOCTL call from timer
    ... Such timer functions are supposed to do ... Not that those sleeping functions sleep every ... will inevitably lead to a kernel panic. ... about doing this in kernel mode and do it in user mode instead. ...
    (comp.os.linux.development.system)
  • 2003 print server - should I use a use kernel mode driver?
    ... 2003 print server? ... Without going into details - the user mode drivers for the HP Color LaserJet ... attached to a 2000 server and need to move them to 2003 server. ... drivers from HP other than the kernel mode one we have been using on 2000 ...
    (microsoft.public.windowsxp.print_fax)
  • Re: process switch...
    ... interrupt occures, in kernel mode it will be delievered and schedular ... Now as kernel 2.4.xx is non preemptive in kernel mode, ... function of my module is running and meanwhile a timer inturrupt ... I came to know about nesting of interrupt handlers, ...
    (comp.os.linux.development.system)