linux-kernel - severe regression with random I/O from (at least) 4.14?

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Date:   Thu, 21 Dec 2017 11:57:48 +0100
From:   Paolo Valente <paolo.valente@...aro.org>
To:     linux-block <linux-block@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Cc:     Linus Walleij <linus.walleij@...aro.org>,
        Ulf Hansson <ulf.hansson@...aro.org>,
        Mark Brown <broonie@...nel.org>,
        DAVIDE FERRARI <162996@...denti.unimore.it>
Subject: severe regression with random I/O from (at least) 4.14?

Hi,
a few minutes ago I bumped into this apparent severe regression, with 4.15-rc4 and an SSD PLEXTOR PX-256M5S. If, with none as I/O scheduler, I do
fio --name=global --rw=randread --size=512m --name=job1

I get
read : io=524288KB, bw=34402KB/s, iops=8600, runt= 15240msec

This device had to reach at least 40 KIOPS. I retried with mq-deadline too, and then with a 4.14, same outcome in all cases. I asked some colleague to repeat the test with his/her device. Same outcome, so far, also with an SSD 850 EVO 250GB.

I'm sorry if I'm making some colossal mistake.

Thanks,
Paolo