ARM: big performance waste in memcpy_{from,to}io
Alexander Clouter
alex at digriz.org.uk
Thu Nov 12 13:44:40 EST 2009
Hubert Feurstein <h.feurstein at gmail.com> wrote:
>
> I'm working with an Contec Micro9 board (ep93xx-based with two Spansion-NOR-
> Flash chips in parallel => 32bit memory-buswidth) and was wondering why the
> read-performance of the flash (through /dev/mtd*) is so quite poor. So I
> connected a logic analyser to the data- and address-bus and recognized that
> the accesses to the same flash-word-address happens four times. This means
> that the flash is read byte-by-byte, which is IMO a big waste of performance
> since it would be possible to read the full word (four bytes) at once. So I
> digged around in the mtd-driver and found the function "memcpy_fromio" which
> is called to read the flash data. I was really surprised when looked to the
> implementation, which is:
>
> [snipped]
>
> Are there any drawbacks when using the good-and-fast "memcpy" ? On my Micro9-
> board everything is running fine so far.
>
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