linux-kernel - Re: io.latency controller apparently not working

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Message-ID: <20190816132124.ggedqxrhi5povqlo@macbook-pro-91.dhcp.thefacebook.com>
Date:   Fri, 16 Aug 2019 09:21:25 -0400
From:   Josef Bacik <josef@...icpanda.com>
To:     Paolo Valente <paolo.valente@...aro.org>
Cc:     linux-block <linux-block@...r.kernel.org>,
        linux-kernel <linux-kernel@...r.kernel.org>,
        Josef Bacik <josef@...icpanda.com>,
        Jens Axboe <axboe@...nel.dk>,
        Vincent Guittot <vincent.guittot@...aro.org>,
        noreply-spamdigest via bfq-iosched 
        <bfq-iosched@...glegroups.com>, Tejun Heo <tj@...nel.org>
Subject: Re: io.latency controller apparently not working

On Fri, Aug 16, 2019 at 12:57:41PM +0200, Paolo Valente wrote:
> Hi,
> I happened to test the io.latency controller, to make a comparison
> between this controller and BFQ.  But io.latency seems not to work,
> i.e., not to reduce latency compared with what happens with no I/O
> control at all.  Here is a summary of the results for one of the
> workloads I tested, on three different devices (latencies in ms):
> 
>              no I/O control        io.latency         BFQ
> NVMe SSD     1.9                   1.9                0.07
> SATA SSD     39                    56                 0.7
> HDD          4500                  4500               11
> 
> I have put all details on hardware, OS, scenarios and results in the
> attached pdf.  For your convenience, I'm pasting the source file too.
> 

Do you have the fio jobs you use for this?  I just tested on Jens's most recent
tree and io.latency appears to be doing what its supposed to be doing.  We've
also started testing 5.2 in production and it's still working in production as
well.  The only thing I've touched recently was around wakeups and shouldn't
have broken everything.  I'm not sure why it's not working for you, but a fio
script will help me narrow down what's going on.  Thanks,

Josef