The patch *WITHOUT* debugging enabled fell over real fast. Now *WITH* debugging the skyrocketin load symptom is gone, and it's chugging along nicely at line speed with FTP and also with CPU maxed out with scp about 20% udner line speed (i.e. saturated CPU). SO far I've moved 4Gb of data with no ill effect, which is a new record. I'll let it
Interesting ... it did have an effect. Not entirely unexpected, though I'm still curious which debug-related delays matter.
play all night with bouncing files around and see if it keels over at some point. The interrupt rate is roughly 9k/sec for the USB controller.
That interrupt rate is absurdly high, considering
- The controller's irq latency is set at 1 microframe, and there are are only 8000 microframes per second. Where would the extra IRQs come from?
- On 2.5 the scatterlist logic cuts the interrupt rate down to one per i/o scatterlist, instead of one per entry. (The scatterlist below is "big", 127 entries.)
At peak rates, EHCI can do about 25 entries per millisecond, many controllers do closer to half that. Call the "average" sglist about 20 entries (close to what I've noticed), and that suggests a peak IRQ rate closer to 1000/sec.
Something would seem to be getting measured wrong, or else there's something else causing a lot of your load problems.
I had no more than typed up my last reply before it fell over...
Jun 10 03:23:57 lapper kernel: usb-storage: Command WRITE_10 (10 bytes) Jun 10 03:23:57 lapper kernel: usb-storage: 2a 00 05 7d 76 37 00 04 00 00 Jun 10 03:23:57 lapper kernel: usb-storage: Bulk command S 0x43425355 T 0x262e Trg 0 LUN 0 L 524288 F 0 CL 10 Jun 10 03:23:57 lapper kernel: usb-storage: usb_stor_bulk_transfer_buf: xfer 31 bytes Jun 10 03:23:57 lapper kernel: usb-storage: Status code 0; transferred 31/31 Jun 10 03:23:57 lapper kernel: usb-storage: -- transfer complete Jun 10 03:23:57 lapper kernel: usb-storage: Bulk command transfer result=0 Jun 10 03:23:57 lapper kernel: usb-storage: usb_stor_bulk_transfer_sglist: xfer 524288 bytes, 127 entries Jun 10 03:24:27 lapper kernel: usb-storage: usb_storage_command_abort called
Interesting -- aborted in the middle of a scatterlist op, instead of the end; and it's a WRITE, not a READ.
I'm setting up for some more tests, with a usb disk and different controllers; maybe something will appear.
- Dave
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