On Thu, 24 Sep 2009, Mikael Pettersson wrote: > I'm trying to tune a tickless 2.6.31 kernel for an ARM box > (arch/arm/mach-iop32x/n2100.c). Looking at /proc/timer_stats > I see that > > usb_hcd_poll_rh_status (rh_timer_func) > > is now the #1 cause of timeouts, which prevents the tickless > kernel from extending the periods between timer interrupts. > > The machine has VIA EHCI and UHCI controllers. The polling timer > appears if UHCI_HCD is enabled; enabling only EHCI_HCD does not > case the timer to appear. What USB devices are on the UHCI buses? > Is a polling timer really necessary? If it is, why? UHCI bug or > kernel limitation/shortcut? It is necessary if the the bus is not suspended. This is a UHCI design limitation, not a bug and not a kernel limitation. Even if the bus is suspended, the timer sometimes is necessary. This is because of bugs in some UHCI implementations and bugs in some motherboard designs. However these bugs are specific to Intel and Genesys Logic controllers and Asus motherboards, so they shouldn't affect you. Alan Stern -- 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
