Messages in this thread | | | Subject | Re: libata/sata_nv latency on NVIDIA CK804 [was Re: AMD64 X2 lost ticks on PM timer] | From | Alan Cox <> | Date | Thu, 16 Mar 2006 15:13:39 +0000 |
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On Mer, 2006-03-15 at 23:00 +0100, Ingo Molnar wrote: > so my guess would be that this device doesnt do MMIO, and the PIO inb() > causes some bad BIOS-based SMM handler/emulator to trigger, which takes > 16.6 msecs. If indeed the device is not in MMIO mode, is there a way to > force it into MMIO mode, to test this theory?
There is a much more reliable way to check this. Use the profiling registers to check the instruction issue count before/after the I/O and you'll know if its something like SMM or just a bus stall.
I can believe the bus stall because some devices will queue a large FIFO of data for the disk and the status read may require flushing it all out.
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