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Groups > linux.kernel > #1279515
| From | Finn Thain <fthain@telegraphics.com.au> |
|---|---|
| Newsgroups | linux.kernel |
| Subject | Re: [PATCH 22/71] ncr5380: Eliminate selecting state |
| Date | 2015-11-30 03:20 +0100 |
| Message-ID | <qAmen-5NT-39@gated-at.bofh.it> (permalink) |
| References | (3 earlier) <qzayB-ZY-3@gated-at.bofh.it> <qzdmO-2Nc-15@gated-at.bofh.it> <qA6sW-4nz-7@gated-at.bofh.it> <qA7p0-4Xu-15@gated-at.bofh.it> <qAaGe-6R8-1@gated-at.bofh.it> |
| Organization | linux.* mail to news gateway |
On Sun, 29 Nov 2015, Geert Uytterhoeven wrote:
> If an ISA access takes 8 us, while the CPU runs at 1 GHz, i.e. 500M
> loops/s, the difference will be huge.
Ondrej showed that an ISA access can take about 1.6 us. I don't know what
to make of the "8 uS" comment in the mainline driver. Maybe it was an even
slower ISA card.
Anyway, I made a measurement on my hardware and confirmed that lpj is a
very bad proxy for device register access throughput. The "loops per
access" gap is several orders of magnitude:
lpj HZ access time (us) lpa
------------------------------------------------------------------------
Ondrej's 5380 ISA card (PC): 4797252 250 1.6 1.9k
My DMX3191D PCI card (PowerMac): 167079 100 0.42 7.0
>
> Perhaps you can calibrate an NCR5380_read() loop at driver init time,
> and use the calibration value later?
I had the same idea but I didn't think that the complexity was justified
by the low precision requirement. But now that I have some timings I have
to agree.
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[PATCH 22/71] ncr5380: Eliminate selecting state Finn Thain <fthain@telegraphics.com.au> - 2015-11-18 10:10 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Ondrej Zary <linux@rainbow-software.org> - 2015-11-24 20:10 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Finn Thain <fthain@telegraphics.com.au> - 2015-11-25 04:20 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Ondrej Zary <linux@rainbow-software.org> - 2015-11-25 23:00 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Finn Thain <fthain@telegraphics.com.au> - 2015-11-26 11:30 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Ondrej Zary <linux@rainbow-software.org> - 2015-11-26 20:40 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Finn Thain <fthain@telegraphics.com.au> - 2015-11-26 23:40 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Ondrej Zary <linux@rainbow-software.org> - 2015-11-29 00:20 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Finn Thain <fthain@telegraphics.com.au> - 2015-11-29 01:50 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Ondrej Zary <linux@rainbow-software.org> - 2015-11-29 10:20 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-29 10:30 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Finn Thain <fthain@telegraphics.com.au> - 2015-11-29 11:30 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Geert Uytterhoeven <geert@linux-m68k.org> - 2015-11-29 15:00 +0100
Re: [PATCH 22/71] ncr5380: Eliminate selecting state Finn Thain <fthain@telegraphics.com.au> - 2015-11-30 03:20 +0100
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