From mboxrd@z Thu Jan  1 00:00:00 1970
From: Sagi Grimberg <sagi@grimberg.me>
Subject: Re: [net 02/14] Revert "mlx5: move affinity hints assignments to
 generic code"
Date: Mon, 25 Dec 2017 15:53:17 +0200
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Cc: netdev@vger.kernel.org, Thomas Gleixner <tglx@linutronix.de>,
        Jes Sorensen <jsorensen@fb.com>
To: Saeed Mahameed <saeedm@mellanox.com>,
        "David S. Miller" <davem@davemloft.net>
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> Before the offending commit, mlx5 core did the IRQ affinity itself,
> and it seems that the new generic code have some drawbacks and one
> of them is the lack for user ability to modify irq affinity after
> the initial affinity values got assigned.
> 
> The issue is still being discussed and a solution in the new generic code
> is required, until then we need to revert this patch.
> 
> This fixes the following issue:
> echo <new affinity> > /proc/irq/<x>/smp_affinity
> fails with  -EIO
> 
> This reverts commit a435393acafbf0ecff4deb3e3cb554b34f0d0664.
> Note: kept mlx5_get_vector_affinity in include/linux/mlx5/driver.h since
 > it is used in mlx5_ib driver.

This won't work for sure because the msi_desc affinity cpumask won't
ever be populated. You need to re-implement it in mlx5 if you don't want
to break rdma ULPs that rely on it.