Messages in this thread | | | Date | Wed, 15 Mar 2006 22:58:48 +0100 | From | Ingo Molnar <> | Subject | Re: libata/sata_nv latency on NVIDIA CK804 [was Re: AMD64 X2 lost ticks on PM timer] |
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* Lee Revell <rlrevell@joe-job.com> wrote:
> On Wed, 2006-03-15 at 16:36 -0500, Bill Rugolsky Jr. wrote: > > <...>-2913 0d.h. 9us : ata_host_intr (nv_interrupt) > > <...>-2913 0d.h. 9us!: ata_bmdma_status (ata_host_intr) > > <...>-2913 0d.h. 16641us : nv_check_hotplug_ck804 (nv_interrupt) > > <...>-2913 0d.h. 16642us : _spin_unlock_irqrestore (nv_interrupt) > > There's your problem - it looks like ata_bmdma_status() stalled the > machine for almost 17ms.
i agree. Here's a bit more detailed analysis: the tracer timestamps function entry points. So what we know is that from the call to ata_bdma_status(), up to the call to nv_check_hotplug_ck804(), 16.6 msecs passed. The codepath includes:
- the whole of the ata_bdma_status() function
- a small portion of ata_host_intr() [from the point where it returns from the ops->bdma_status() call up to the return]
- and a small portion of nv_interrupt(), from the ata_host_intr() return to the ->check_hotplug() call.
in this particular case there's only very simple (and non-IO) instructions in that codepath (no loops either), except for ata_bmdma_status() which does IO ops: so i agree with you that the most likely candidate for the delay is the readb() or the inb() in ata_bdma_status().
I'm wondering which one of the two. inb()s are known to be horrible on some systems - but i've never seen them take 16 milliseconds. If it's the inb(), then that could also involve SMM mode and IO emulation/bug-workaround BIOS hackery - which could indeed cause such delays. [but i havent seen such a thing either.]
the other option is that this is a random delay [e.g. DMA starvation] hitting ata_bmdma_status() only by accident. (That looks a bit unlikely though, given how related this codepath seems to the whole problem area.)
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