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Re: [PATCH v2 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers

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On Fri, Sep 9, 2016 at 1:28 PM, Martin K. Petersen
<martin.petersen@oracle.com> wrote:
>>>>>> "Finn" == Finn Thain <fthain@telegraphics.com.au> writes:
>
> Finn> Large PIO transfers are broken up into chunks to try to avoid
> Finn> disabling local IRQs for long periods. But IRQs are still disabled
> Finn> for too long and this causes SCC FIFO overruns during serial port
> Finn> transfers.
>
> Finn> This patch reduces the PIO chunk size to reduce interrupt latency
> Finn> to something on the order of milliseconds, at the expense of
> Finn> additional CPU overhead from extra iterations of the
> Finn> NCR5380_main() loop.
>
> Finn> That CPU overhead is a problem for slow machines (e.g. mac_scsi on
> Finn> 25 MHz
> Finn> 68030) but these machines generally use PDMA not PIO. This patch
> Finn>        doesn't
> Finn> make the overhead any worse on my Mac LC III (because it only gets
> Finn> about 510 accesses per ms).
>
> Finn> This patch decreases disk performance by a fraction of one percent
> Finn> for dmx3191d on my 333 MHz PowerPC 750. Other affected hardware
> Finn> (such as g_NCR5380 on x86) was not tested but 5380 ISA cards
> Finn> generally use PDMA and not PIO.
>
> Geert?

No comments from my side.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@linux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds

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[PATCH 0/3] Small fixes and cleanup Finn Thain <fthain@telegraphics.com.au> - 2016-08-27 04:50 +0200
  [PATCH 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers Finn Thain <fthain@telegraphics.com.au> - 2016-08-27 04:50 +0200
    Re: [PATCH 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers Geert Uytterhoeven <geert@linux-m68k.org> - 2016-08-28 10:10 +0200
      Re: [PATCH 3/3] scsi/ncr5380: Improve interrupt latency during PIO  tranfers Finn Thain <fthain@telegraphics.com.au> - 2016-08-29 06:20 +0200
    [PATCH v2 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers Finn Thain <fthain@telegraphics.com.au> - 2016-08-31 07:10 +0200
      Re: [PATCH v2 3/3] scsi/ncr5380: Improve interrupt latency during  PIO tranfers Laurence Oberman <loberman@redhat.com> - 2016-08-31 16:10 +0200
      Re: [PATCH v2 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers "Martin K. Petersen" <martin.petersen@oracle.com> - 2016-09-09 13:30 +0200
        Re: [PATCH v2 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers Geert Uytterhoeven <geert@linux-m68k.org> - 2016-09-09 14:10 +0200
      Re: [PATCH v2 3/3] scsi/ncr5380: Improve interrupt latency during PIO tranfers "Martin K. Petersen" <martin.petersen@oracle.com> - 2016-09-14 20:20 +0200
  Re: [PATCH 0/3] Small fixes and cleanup "Martin K. Petersen" <martin.petersen@oracle.com> - 2016-08-31 06:30 +0200

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