linux-kernel - Re: [PATCH blk-next 1/2] blk-mq-rdma: Delete not-used multi-queue RDMA map queue code

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Message-ID: <20201006045800.GE1874917@unreal>
Date:   Tue, 6 Oct 2020 07:58:00 +0300
From:   Leon Romanovsky <leon@...nel.org>
To:     Christoph Hellwig <hch@....de>
Cc:     Sagi Grimberg <sagi@...mberg.me>,
        Doug Ledford <dledford@...hat.com>,
        Jason Gunthorpe <jgg@...dia.com>, Jens Axboe <axboe@...nel.dk>,
        Keith Busch <kbusch@...nel.org>, linux-block@...r.kernel.org,
        linux-kernel@...r.kernel.org, linux-nvme@...ts.infradead.org,
        linux-rdma@...r.kernel.org
Subject: Re: [PATCH blk-next 1/2] blk-mq-rdma: Delete not-used multi-queue
 RDMA map queue code

On Mon, Oct 05, 2020 at 10:38:17AM +0200, Christoph Hellwig wrote:
> On Fri, Oct 02, 2020 at 01:20:35PM -0700, Sagi Grimberg wrote:
> >> Well, why would they change it?  The whole point of the infrastructure
> >> is that there is a single sane affinity setting for a given setup. Now
> >> that setting needed some refinement from the original series (e.g. the
> >> current series about only using housekeeping cpus if cpu isolation is
> >> in use).  But allowing random users to modify affinity is just a receipe
> >> for a trainwreck.
> >
> > Well allowing people to mangle irq affinity settings seem to be a hard
> > requirement from the discussions in the past.
> >
> >> So I think we need to bring this back ASAP, as doing affinity right
> >> out of the box is an absolute requirement for sane performance without
> >> all the benchmarketing deep magic.
> >
> > Well, it's hard to say that setting custom irq affinity settings is
> > deemed non-useful to anyone and hence should be prevented. I'd expect
> > that irq settings have a sane default that works and if someone wants to
> > change it, it can but there should be no guarantees on optimal
> > performance. But IIRC this had some dependencies on drivers and some
> > more infrastructure to handle dynamic changes...
>
> The problem is that people change random settings.  We need to generalize
> it into a sane API (e.g. the housekeeping CPUs thing which totally makes
> sense).

I don't see many people jump on the bandwagon, someone should do it, but
who will? I personally have no knowledge in that area to do anything
meaningful.

Thanks