Messages in this thread | | | Date | Thu, 06 Jan 2005 18:40:40 -0500 | From | Jeff Garzik <> | Subject | Re: page fault scalability patch V12 [0/7]: Overview and performance tests |
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Andy Warner wrote: > Jeff Garzik wrote: > >>[...] >>I am currently chasing a 2.6.8->2.6.9 SATA regression, which causes >>ata_piix (Intel ICH5/6/7) to not-find some SATA devices on x86-64 SMP, >>but works on UP. Potentially related to >=4GB of RAM. >> >> >> >>Details, in case anyone is interested: >>Unless my code is screwed up (certainly possible), PIO data-in [using >>the insw() call] seems to return all zeroes on a true-blue SMP machine, >>for the identify-device command. When this happens, libata (correctly) >>detects a bad id page and bails. (problem doesn't show up on single CPU >>w/ HT) > > > Ah, I might have been here recently, with the pass-thru stuff. > > What I saw was that in an SMP machine: > > 1. queue_work() can result in the work running (on another > CPU) instantly. > > 2. Having one CPU beat on PIO registers reading data from one port > would significantly alter the timing of the CMD->BSY->DRQ sequence > used in PIO. This behaviour was far worse for competing ports > within one chip, which I put down to arbitration problems. > > 3. CPU utilisation would go through the roof. Effectively the > entire pio_task state machine reduced to a busy spin loop. > > 4. The state machine needed some tweaks, especially in error > handling cases. > > I made some changes, which effectively solved the problem for promise > TX4-150 cards, and was going to test the results on other chipsets > next week before speaking up. Specifically, I have seen some > issues with SiI 3114 cards. > > I was trying to explore using interrupts instead of polling state > but for some reason, I was not getting them for PIO data operations, > or I misunderstand the spec, after removing ata_qc_set_polling() - again > I saw a difference in behaviour between the Promise & SiI cards > here. > > I'm about to go offline for 3 days, and hadn't prepared for this > yet. The best I can do is provide a patch (attached) that applies > against 2.6.9. It also seems to apply against libata-2.6, but > barfs a bit against libata-dev-2.6. > > The changes boil down to these: > > 1. Minor changes in how status/error regs are read. > Including attempts to use altstatus, while I was > exploring interrupts. > > 2. State machine logic changes. > > 3. Replace calls to queue_work() with queue_delayed_work() > to stop SMP machines going crazy. > > With these changes, on a platform consisting of 2.6.9 and > Promise TX4-150 cards, I can move terabytes of parallel > PIO data, without error. > > My gut says that the PIO mechanism should be overhauled, I > composed a "how much should we pay for this muffler" email > to linux-ide at least twice while working on this, but never > sent it - wanting to send a solution in rather than just > making more comments from the peanut gallery. > > I'll pick up the thread on this next week, when I'm back online. > I hope this helps.
Please let me know if you still have problems?
The PIO SMP problems seem to be fixed here.
Jeff
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