Re: [PATCH 2.6.13-rc1 03/10] IOCHK interface for I/O error handling/detecting

From: Benjamin Herrenschmidt (benh_at_kernel.crashing.org)
Date: 07/13/05

  • Next message: Rob Mueller: "Re: 2.6.12.2 dies after 24 hours" 
    To: Linas Vepstas <linas@austin.ibm.com>
Date:	Wed, 13 Jul 2005 10:18:57 +1000

    > Are you assuming that a device driver will use an iochk_read() for
    > every DMA operation? for every MMIO to the card?
    >
    > For high performance devices, it seems to me that this will cause
    > a rather large performance burden, especially if its envisioned that
    > all architectures will do something similar.
    >
    > My concern is that (at least on ppc64) the call pci_read_config_word()
    > requires a call into "firmware" aka "BIOS", which takes thousands upon
    > thousands of cpu cycles. There are hundreds of cycles of gratuitous
    > crud just to get into the firmware, and then lord-knows-what the
    > firmware does while its in there; probably doing all sorts of crazy
    > math to compute bus addresses and other arcane things. I would imagine
    > that most architectures, includig ia64, are similar.
    >
    > Thus, one wouldn't want to perform an iochk_read() in this way unless
    > one was already pretty sure that an error had already occured ...
    >
    > Am I misunderstanding something?

    I would expect pSeries not to use the "default" error checking (that
    tests the status register) but rather use EEH.

    Ben.

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