From: Joe Thornber <thornber redhat com>
To: Jagan Reddy <gjmsreddy yahoo com>; device-mapper development <dm-devel redhat com>
Sent: Friday, January 20, 2012 10:07 AM
Subject: Re: [dm-devel] dm-thin vs lvm performance
On Fri, Jan 20, 2012 at 05:33:34PM +0000, Joe Thornber wrote:
> Back to testing ...
Here are my aio-stress results for various devices running on top of a
| Device stack | M/s |
| raw ramdisk | 5440 |
| linear | 5431 |
| 2 stacked linear | 5304 |
| pool device | 5351 |
| linear stacked on pool | 5243 |
| thin | 5375 |
I also tried the thin test after disabling the block locking in
dm-block-manager.c, and using a 128 entry cache local to the thin
device. Neither made any difference to the 'thin' result.
Things for you to check:
i) Are you benchmarking
with a ramdisk, or your flash device? In both
cases I think you need to make sure the device has allocated backing
store before you run any tests. Remember that Discards may well
removing this backing.
ii) You claim that io is getting deferred. This will happen when you do
the initial wipe of the thin device to force provisioning. But for
the aio-stress tests you should get nothing deferred (I instrumented
to confirm this).