On 8/17/18 11:39 AM, Ricardo Ribalda Delgado wrote:

Hello Paolo
On Fri, Aug 17, 2018 at 7:35 PM Paolo Valente [off-list ref] wrote:

quoted

quoted

Il giorno 17 ago 2018, alle ore 19:31, Ricardo Ribalda Delgado [off-list ref] ha scritto:

Hello

Coming from: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=906328

bmaptools is kind of a "smart dd" tool, that lets you write images
very fast and securely. Since the last Debian Kernel update it has
become 5-8 times slower.

After some debugging, we have figured out that the reason for that
slowness is the Multi-Queue Block IO Queueing Mechanism.

Debian maintainer has pointed out that in the near future the single
queue will be deprecated.

My question is if we can get a similar perfomance for bmaptools with
blk-mq and how?

Have you also checked what happens after switching to a different I/O
scheduler for the involved drive (among none, mq-deadline, bfq and
kyber)?

I have only tried mq-deadline and none (because they are enabled by
default on Debian). Both produce results in the same range: 5-8 times
slower.

I could easily enable kyber:
cat /boot/config-4.17.0-1-amd64  | grep CONFIG_MQ_IOSCHED
CONFIG_MQ_IOSCHED_DEADLINE=y
CONFIG_MQ_IOSCHED_KYBER=m

But I left the card reader on the office, so any test would have to
wait until monday sorry :(

Can someone describe what bmaptools does? IOW, how is it different than
dd? Does it use multiple threads for both reads and writes?

-- 
Jens Axboe