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SubjectRe: new Areca driver in 2.6.16-rc6-mm2 appears to be broken
Date
Dear Jens Axboe,

I had found a big difference of generic_make_request(struct bio *bio)
got message : sdb1: rw=0, want=...., limit=.....

*****************
** TEST 1
*****************
I used "MAX_XFER_SECTORS 4096" driver to do mkfs.ext2 with ARECA RAID
volume sdb1.
and copy a big file (900MB) into sdb1.
If I copy this file from sdb1, the message rw=.... ,want=......,
limit=...... will appear immediately.
When I reboot the system and used "MAX_XFER_SECTORS 512" driver.
I copy this big file from sdb1, the message rw=.... ,want=......,
limit=...... still appear immediately.
When I redo mkfs.ext2 with ARECA RAID volume sdb1 (used "MAX_XFER_SECTORS
512")
and copy the same file (900MB) into sdb1.
I copy this file from sdb1 again,the message rw=.... ,want=......,
limit=...... disappear.
****************
** TEST 2
****************
When I do another test with "MAX_XFER_SECTORS 4096" driver

#echo 0 > /sys/block/sdb/queue/read_ahead_kb
#mkfs.ext2 /dev/sdb1
then copy the same file (900MB) into sdb1.
I copy this file from sdb1 again,the message rw=.... ,want=......,
limit=...... disappear.
Even I redo "echo 4096 > /sys/block/sdb/queue/read_ahead_kb" with ARECA RAID
volume.
The message rw=.... ,want=......, limit=...... never appear at my "copy
compare" test script.
Now I can say the bug come from "block read ahead".

And this bug will certainly appear when do "mkfs.ext2" if read_ahead_kb
value large enough.


Best Regards
Erich Chen
----- Original Message -----
From: "Jens Axboe" <axboe@suse.de>
To: "Andrew Morton" <akpm@osdl.org>
Cc: "James Bottomley" <James.Bottomley@steeleye.com>; <erich@areca.com.tw>
Sent: Friday, March 31, 2006 3:42 PM
Subject: Re: new Areca driver in 2.6.16-rc6-mm2 appears to be broken

>
> (irk, Erich wasn't in the cc, sorry to Andrew and James for getting this
> mail twice)
>
> On Thu, Mar 30 2006, Andrew Morton wrote:
>> "erich" <erich@areca.com.tw> wrote:
>> >
>> > Dear Chris Caputo,
>> >
>> > Thanks you to conform this issue again, my colleague assisted me and
>> > to
>> > double check my older version driver yesterday.
>> > and the old driver is working fine as your mention before.
>> >
>> > The ARCMSR_MAX_XFER_SECTORS is the reason why cause "attempt to access
>> > beyond end of device".
>> >
>> > #define ARCMSR_MAX_XFER_SECTORS
>> > 256 -----old
>> > #define ARCMSR_MAX_XFER_SECTORS
>> > 4096 -----new
>>
>> That seems odd. ARCMSR_MAX_XFER_SECTORS just gets put into
>> scsi_host_template.max_sectors. Could it be a scsi core buglet?
>
> Perhaps the larger max sectors setting is causing read-ahead to be
> overly optimistic and going beyond the end? Should not happen.
>
> Erich, can you try and shrink read-ahead on that device and retest?
> Basically just do
>
> # echo 0 > /sys/block/sdX/queue/read_ahead_kb
>
> and see if it still complains.
>
> --
> Jens Axboe
>

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