netdev - Re: [net 02/14] Revert "mlx5: move affinity hints assignments to generic code"

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Date:   Tue, 26 Dec 2017 07:58:22 -0800
From:   Saeed Mahameed <saeedm@....mellanox.co.il>
To:     Sagi Grimberg <sagi@...mberg.me>
Cc:     Saeed Mahameed <saeedm@...lanox.com>,
        "David S. Miller" <davem@...emloft.net>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Thomas Gleixner <tglx@...utronix.de>,
        Jes Sorensen <jsorensen@...com>
Subject: Re: [net 02/14] Revert "mlx5: move affinity hints assignments to
 generic code"

On Mon, Dec 25, 2017 at 5:53 AM, Sagi Grimberg <sagi@...mberg.me> wrote:
>
>> 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.

Are you sure it won't get populated at all  ? even if you manually set
IRQ affinity via sysfs ?
Anyway we can implement this driver helper function to return the IRQ
affinity hint stored in the driver:
 "cpumask_first(mdev->priv.irq_info[vector].mask);"