linux-kernel - Re: bfq-mq performance comparison to cfq

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Date:   Tue, 11 Apr 2017 09:29:46 +0200
From:   Paolo Valente <paolo.valente@...aro.org>
To:     Bart Van Assche <bart.vanassche@...disk.com>
Cc:     "aherrmann@...e.com" <aherrmann@...e.com>,
        "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        "linux-block@...r.kernel.org" <linux-block@...r.kernel.org>,
        "axboe@...nel.dk" <axboe@...nel.dk>
Subject: Re: bfq-mq performance comparison to cfq


> Il giorno 10 apr 2017, alle ore 17:15, Bart Van Assche <bart.vanassche@...disk.com> ha scritto:
> 
> On Mon, 2017-04-10 at 11:55 +0200, Paolo Valente wrote:
>> That said, if you do always want maximum throughput, even at the
>> expense of latency, then just switch off low-latency heuristics, i.e.,
>> set low_latency to 0.  Depending on the device, setting slice_ilde to
>> 0 may help a lot too (as well as with CFQ).  If the throughput is
>> still low also after forcing BFQ to an only-throughput mode, then you
>> hit some bug, and I'll have a little more work to do ...
> 
> Hello Paolo,
> 
> Has it been considered to make applications tell the I/O scheduler
> whether to optimize for latency or for throughput? It shouldn't be that
> hard for window managers and shells to figure out whether or not a new
> application that is being started is interactive or not. This would
> require a mechanism that allows applications to provide such information
> to the I/O scheduler. Wouldn't that be a better approach than the I/O
> scheduler trying to guess whether or not an application is an interactive
> application?
> 

IMO that would be an (or maybe the) optimal solution, in terms of both
throughput and latency.  We have even developed a prototype doing what
you propose, for Android.  Unfortunately, I have not yet succeeded in
getting support, to turn it into candidate production code, or to make
a similar solution for lsb-compliant systems.

Thanks,
Paolo


> Bart.