Messages in this thread | | | Date | Sun, 4 Apr 2010 18:39:24 +0200 | From | Dominik Brodowski <> | Subject | Re: A few questions and issues with dynticks, NOHZ and powertop |
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On Sun, Apr 04, 2010 at 11:17:37AM -0400, Alan Stern wrote: > On Sun, 4 Apr 2010, Dominik Brodowski wrote: > > > Booting a SMP-capable kernel with "nosmp", or manually offlining one CPU > > (or -- though I haven't tested it -- booting a SMP-capable kernel on a > > system with merely one CPU) means that in up to about half of the calls to > > tick_nohz_stop_sched_tick() are aborted due to rcu_needs_cpu(). This is > > quite strange to me: AFAIK, RCU is an excellent tool for SMP, but not really > > needed for UP? > > I can't answer the real question here, not knowing enough about the RCU > implementation. However, your impression is wrong: RCU very definitely > _is_ useful and needed on UP systems. It coordinates among processes > (and interrupt handlers) as well as among processors.
Okay, but still: can't this be sped up by much on UP (especially if CONFIG_RCU_FAST_NO_HZ is set), so that we can go to sleep right away?
> > 3) USB: built-in UHCI and a built-in 0a5c:2101 Broadcom Corp. A-Link > > BlueUsbA2 Bluetooth module; built-in EHCI and a built-in 0ac8:c302 Z-Star > > Microelectronics Corp. Vega USB 2.0 Camera. > > > > usbcore.autosuspend is enabled (= 2), of course. > > > > Recent USB suspend statistics > > Active Device name > > 100.0% USB device 7-1 : BCM92045NMD (Broadcom Corp) > > 100.0% USB device 1-2 : Vega USB 2.0 Camera. (Vimicro Corp.) > > 100.0% USB device usb7 : UHCI Host Controller (Linux 2.6.34-rc3 uhci_hcd) > > 100.0% USB device usb1 : EHCI Host Controller (Linux 2.6.34-rc3 ehci_hcd) > > > > Booting into /bin/bash on a SMP kernel booted with "nosmp" leads to ~ 10 > > wakeups per second; disabling the cursor helps halfway (~ 5 wakeups); and > > manually unbinding the USB host drivers from the USB host devices finally > > lead to ~ 1.1 wakeups per second. What's keeping USB from suspending these > > unused devices here? > > Either the drivers don't support autosuspend or the devices aren't > enabled for autosuspend. By default, autosuspend is disabled for > (almost) all non-hub devices. You or your distribution must enable > it manually by doing: > > echo auto >/sys/bus/usb/devices/.../power/level > > If the driver doesn't support autosuspend then enabling it won't be > enough; you'll also have to unbind the driver from the device. The > easiest way to do this is to unconfigure the device: > > echo 0 >/sys/bus/usb/devices/.../bConfigurationValue
Thanks! This way, it works, even without manually unbinding the host drivers.
Best, Dominik
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