[dm-crypt] dm-crypt perf related changes and cryptsetup LUKS format failing

Milan Broz gmazyland at gmail.com
Fri Feb 7 15:42:51 CET 2014


On 02/07/2014 02:53 PM, Redwood Hyd wrote:
> Hi All ,
> 
> I did an experimental kernel change in linux/drivers/md/dm-crypt.c for
> improving crypto HW performance.
> Here is brief of it
> static void crypt_io_hints(struct dm_target *ti,
>                             struct queue_limits *limits)
> {
>   limits->physical_block_size = 32768;
>   blk_limits_io_min(limits, 32768);
>   blk_limits_io_opt(limits, 32768);
> }
> 
> It works (passed iozone -a,  robocopy from samba client) and doubled
> performance of dm-crypt WRITES !

Well, increasing encryption block size was discussed several times.

Please search archive, e.g. here is some patch which increased block size:
http://thread.gmane.org/gmane.linux.kernel.device-mapper.dm-crypt/6441/focus=6587

(yes, your patch is just modification of io limits, which is simpler but has some
side effects - random io read/write will be worse I guess)


> Problem -
> After above change cryptsetup luks format started failing disk
> validations so additionally in
> Cryptsetup-1.1.3  I  did  following changes to pass disk validation:

Why are you using version released 4 years ago? :)

Try recent 1.6.3. It works without changes.

(Btw your changes to cryptsetup are not correct, it will just paperback over
real problem and cause LUKS format incompatibility.)

Actually, this is what I see after you patch (x is activated LUKS device):

# lsblk -t /dev/sdb

NAME ALIGNMENT MIN-IO OPT-IO PHY-SEC LOG-SEC ROTA SCHED RQ-SIZE  RA WSAME
sdb          0    512      0     512     512    1 cfq       128 128   32M
`-x          0  32768  32768   32768     512    1           128 128    0B

# lsblk -f /dev/sdb
NAME FSTYPE      LABEL UUID                                 MOUNTPOINT
sdb  crypto_LUKS       fc534366-6be5-46f3-9349-44dbe47f4b80 
`-x  ext4              6dfa13d0-2d0e-4955-a5c4-bd0848b07b47 /mnt/tst

so IO limits works...

Milan


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