On 2015-08-01 01:47, Brian Norris wrote:
> On Sat, Aug 01, 2015 at 01:35:52AM +0200, Stefan Agner wrote:
>> On 2015-08-01 01:09, Brian Norris wrote:
>
>> >> +static int vf610_nfc_read_page(struct mtd_info *mtd, struct nand_chip *chip,
>> >> + uint8_t *buf, int oob_required, int page)
>> >> +{
>> >> + int eccsize = chip->ecc.size;
>> >> + int stat;
>> >> +
>> >> + vf610_nfc_read_buf(mtd, buf, eccsize);
>> >> +
>> >> + if (oob_required)
>> >> + vf610_nfc_read_buf(mtd, chip->oob_poi, mtd->oobsize);
>> >
>> > To fix the bitflips issue above, you'll just want to unconditionally
>> > read the OOB (it's fine to ignore 'oob_required') and...
>> >
>> >> +
>> >> + stat = vf610_nfc_correct_data(mtd, buf);
>> >
>> > ...pass in chip->oob_poi as a third argument.
>> >
>>
>> Hm, this probably will have an effect on performance, since we usually
>> omit the OOB if not requested.
>
> You could test :) I don't really like performance claims without tests.
> (I say this because I added the oob_required flag myself, but just for
> functional purposes, not performance. Many drivers got by just fine by
> always copying the OOB data.)
Did the measurement:
As is:
...
[ 30.955675] mtd_speedtest: testing eraseblock write speed
[ 143.349572] mtd_speedtest: eraseblock write speed is 4641 KiB/s
[ 143.355606] mtd_speedtest: testing eraseblock read speed
[ 183.816690] mtd_speedtest: eraseblock read speed is 12893 KiB/s
[ 185.874702] mtd_speedtest: testing page write speed
[ 302.608719] mtd_speedtest: page write speed is 4468 KiB/s
[ 302.614229] mtd_speedtest: testing page read speed
[ 343.831663] mtd_speedtest: page read speed is 12656 KiB/s
...
Unconditionally read OOB:
...
[ 29.076983] mtd_speedtest: testing eraseblock write speed
[ 140.829920] mtd_speedtest: eraseblock write speed is 4667 KiB/s
[ 140.835960] mtd_speedtest: testing eraseblock read speed
[ 181.594498] mtd_speedtest: eraseblock read speed is 12798 KiB/s
[ 183.652793] mtd_speedtest: testing page write speed
[ 299.772069] mtd_speedtest: page write speed is 4492 KiB/s
[ 299.777583] mtd_speedtest: testing page read speed
[ 341.283668] mtd_speedtest: page read speed is 12568 KiB/s
...
And with conditional OOB again, reading OOB if required in
vf610_nfc_correct_data.
...
[ 29.907147] mtd_speedtest: testing eraseblock write speed
[ 141.146171] mtd_speedtest: eraseblock write speed is 4689 KiB/s
[ 141.152185] mtd_speedtest: testing eraseblock read speed
[ 181.644380] mtd_speedtest: eraseblock read speed is 12883 KiB/s
[ 183.703198] mtd_speedtest: testing page write speed
[ 299.423179] mtd_speedtest: page write speed is 4507 KiB/s
[ 299.428671] mtd_speedtest: testing page read speed
[ 340.695925] mtd_speedtest: page read speed is 12640 KiB/s
[ 342.747510] mtd_speedtest: testing 2 page write speed
...
The last test is probably pointless since we never read a empty page in
the speedtest. So performance hit is measurable but small (somewhat
below 100KiB/s).
This is with 64 bytes OOB. Since OOB sizes are only getting bigger, I
would rather still consider it... What do you think?
--
Stefan
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