On Tue, Jan 26, 2010 at 10:45:20PM +0100, Andi Kleen wrote: > jeff@xxxxxxxxxxxx (Jeff Garrett) writes: > > > Hi, > > > > I was trying to chase down a theory that my desktop machine (a core i7) > > is running warm (the fan sounds like it's at full speed all the time, > > and I think it's not always acted this way -- hence the theory). > > > > powertop is never showing it spending any time in C3... > > > > I compiled a kernel without USB/sound/radeon, and ran without X. I was > > able to get the wakeups/sec down below 20, but no time is spent in C3. > > [...] > > This may be a complete red herring, but I added some printk logic to > > acpi_idle_bm_check(), and it is getting called often, but bm_status is > > always 1. [I infer from this that the idle logic is trying to go into > > C3, but this check is stopping it... Unless I misread something.] > > Normally a Core i7 (or any modern Intel systems) should not use > bm_check at all. That's only for older systems that didn't support > MWAIT with c-state hint, but relied on the old port based interface. bm_check = 1, bm_control = 0 I don't know what any of this means. :) I tried changing processor_idle.c. It reads (for C3): 1106 state->enter = pr->flags.bm_check ? 1107 acpi_idle_enter_bm : 1108 acpi_idle_enter_simple; So it always calls acpi_idle_enter_bm in my case. I tried modifying it to call acpi_idle_enter_simple for entering C3 instead. When I did this, it did make it into C3 according to powertop, but the wakeups per second grew by at least 10x. I couldn't get that below ~400-800/s, and the residency in C3 was limited to about ~50%, as reported by powertop. > So something is already confused there. Might just be me. :) > I think it should still work though. > Of course if you really have a lot of bus mastering in the background > then yes there will be no C3. > > -Andi I have no idea what counts as bus mastering (is it just DMA transfers to PCI devices?)... But with a fairly idle system, with things like USB configured out, what could be doing it if it exists? Would there be some nice function I could instrument with a few printk's to, to see? I compiled with PCI_DEBUG=y, and "bus master" doesn't show up in the dmesg. -Jeff -- To unsubscribe from this list: send the line "unsubscribe linux-acpi" in the body of a message to majordomo@xxxxxxxxxxxxxxx More majordomo info at http://vger.kernel.org/majordomo-info.html
