From: Pat LaVarre <p.lavarre@ieee.org>
To: linux-scsi@vger.kernel.org
Subject: aligned /dev/scd$n reads less rare how
Date: 29 Sep 2003 11:55:21 -0600 [thread overview]
Message-ID: <1064858121.4262.0.camel@patehci2> (raw)
In-Reply-To: <1064850600.25057.7.camel@patehci2>
Anything easy I can do to make aligned reads more common?
I ask because often thru /dev/scd$n I see seemingly pointless
misalignment, for example, if I read a 1 GiB disk:
$ sudo blockdev --flushbufs /dev/scd0
$ time sudo dd if=/dev/scd0 bs=1M
...
usb-storage: x 43 00 00 00 00 00 00 00 0C 00
usb-storage: x 43 02 00 00 00 00 01 00 0C 00
usb-storage: x 1E 00 00 00 01 00
usb-storage: x 00 00 00 00 00 00
usb-storage: x 28 00 00 00 00 00 00 00 20 00
usb-storage: x 28 00 00 00 00 20 00 00 24 00
usb-storage: x 28 00 00 00 00 44 00 00 40 00
usb-storage: x 28 00 00 00 00 84 00 00 40 00
usb-storage: x 28 00 00 00 00 C4 00 00 40 00
...
usb-storage: x 28 00 00 07 FE C4 00 00 40 00
usb-storage: x 28 00 00 07 FF 04 00 00 06 00
usb-storage: x 28 00 00 07 FF 0A 00 00 3A 00
usb-storage: x 28 00 00 07 FF 44 00 00 40 00
usb-storage: x 28 00 00 07 FF 84 00 00 0A 00
usb-storage: x 28 00 00 07 FF 8E 00 00 36 00
usb-storage: x 28 00 00 07 FF C4 00 00 3C 00
...
1024+0 records in
1024+0 records out
real 0m54.809s
user 0m0.015s
sys 0m9.039s
$
Pat LaVarre
P.S.
I know I can read aligned thru /dev/sg0 as follows.
$
$ time sudo sg_dd if=/dev/sg0 bs=2k bpt=512 count=524288
of=/mnt/hda11/z.bin
...
Attached scsi generic sg0 at scsi1, channel 0, id 0, lun 0, type 5
usb-storage: x 28 00 00 00 00 00 00 02 00 00
usb-storage: x 28 00 00 00 02 00 00 02 00 00
usb-storage: x 28 00 00 00 04 00 00 02 00 00
usb-storage: x 28 00 00 00 06 00 00 02 00 00
...
usb-storage: x 28 00 00 07 FA 00 00 02 00 00
usb-storage: x 28 00 00 07 FC 00 00 02 00 00
usb-storage: x 28 00 00 07 FE 00 00 02 00 00
524288+0 records in
524288+0 records out
real 0m56.567s
user 0m0.027s
sys 0m7.236s
$
I see this approach to aligning reads slowed me down a second or two.
next prev parent reply other threads:[~2003-09-29 17:55 UTC|newest]
Thread overview: 50+ messages / expand[flat|nested] mbox.gz Atom feed top
2003-09-22 22:55 [linux-usb-devel] Re: USB storage problems on OHCI Pat LaVarre
2003-09-29 14:54 ` Pat LaVarre
2003-09-29 15:50 ` 2 KiB/block loopback found where Pat LaVarre
2003-09-29 16:46 ` Jens Axboe
2003-09-29 17:12 ` Pat LaVarre
2003-09-29 20:02 ` Pat LaVarre
2003-10-06 17:12 ` max GiB written per boot Pat LaVarre
2003-10-06 18:12 ` writable mmc profiles actually are writable Pat LaVarre
2003-10-06 18:22 ` Jens Axboe
2003-10-06 18:25 ` Jens Axboe
2003-10-06 19:50 ` Pat LaVarre
2003-10-06 20:38 ` Jens Axboe
2003-10-06 20:58 ` Pat LaVarre
2003-10-06 22:14 ` Pat LaVarre
2003-10-06 23:56 ` Pat LaVarre
2003-10-07 5:38 ` Jens Axboe
2003-10-07 6:45 ` Matthew Dharm
2003-10-07 6:48 ` Jens Axboe
2003-10-07 7:00 ` Matthew Dharm
2003-10-07 7:04 ` Jens Axboe
2003-10-10 20:36 ` Pat LaVarre
2003-10-10 21:04 ` Pat LaVarre
2003-10-10 21:25 ` Pat LaVarre
2003-10-10 22:43 ` Pat LaVarre
2003-10-10 23:16 ` Pat LaVarre
2003-10-11 0:43 ` Pat LaVarre
2003-10-07 20:46 ` Pat LaVarre
2003-10-07 21:00 ` Jens Axboe
2003-10-09 23:01 ` Pat LaVarre
2003-10-07 7:00 ` Jens Axboe
2003-10-06 20:10 ` Pat LaVarre
2003-10-06 20:28 ` Jens Axboe
2003-10-06 20:21 ` Pat LaVarre
2003-10-06 20:33 ` Jens Axboe
2003-10-06 21:00 ` max GiB written per boot Pat LaVarre
2003-10-06 23:47 ` Pat LaVarre
2003-10-07 5:57 ` Jens Axboe
2003-10-07 22:12 ` Randy.Dunlap
2003-10-07 22:57 ` Willem Riede
2003-10-08 1:27 ` Randy.Dunlap
2003-10-08 4:34 ` Randy.Dunlap
2003-10-08 6:44 ` Jens Axboe
2003-10-09 21:59 ` Pat LaVarre
2003-10-10 20:54 ` Pat LaVarre
2003-10-07 0:51 ` 2 KiB/block loopback found where Pat LaVarre
2003-09-29 17:55 ` Pat LaVarre [this message]
2003-09-29 19:39 ` zip of GiB cross-platform Pat LaVarre
2003-09-29 19:50 ` Matthew Wilcox
2003-09-29 19:56 ` Pat LaVarre
2003-10-24 14:41 ` aligned /dev/scd$n reads less rare how Pat LaVarre
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