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

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Date:   Fri, 2 Oct 2020 08:45:05 +0200
From:   Christoph Hellwig <hch@....de>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     Leon Romanovsky <leon@...nel.org>, Christoph Hellwig <hch@....de>,
        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 Tue, Sep 29, 2020 at 11:24:49AM -0700, Sagi Grimberg wrote:
> Yes, basically usage of managed affinity caused people to report
> regressions not being able to change irq affinity from procfs.

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.

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.