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    Subject[PATCH] irqchip/gic-v3-its: Select housekeeping CPUs preferentially for managed IRQs
    Date
    When using kernel parameter 'isolcpus=managed_irq,xxxx' to bind the
    managed IRQs to housekeeping CPUs, the effective_affinity sometimes
    still contains the non-housekeeping CPUs.

    irq_do_set_affinity() passes the housekeeping cpumask to
    chip->irq_set_affinity(), but ITS driver select CPU according to
    irq_common_data->affinity. While 'irq_common_data->affinity' is updated
    after chip->irq_set_affinity() is called in irq_do_set_affinity(). Also
    'irq_common_data->affinity' may contains non-housekeeping CPUs. I found
    the below link explaining the reason.
    https://www.mail-archive.com/linux-kernel@vger.kernel.org/msg2267032.html

    To modify CPU selecting logic to prefer housekeeping CPUs, select CPU
    from the input cpumask parameter first. If none of it is online, then
    select CPU from 'irq_common_data->affinity'.

    Signed-off-by: Xiongfeng Wang <wangxiongfeng2@huawei.com>
    ---
    drivers/irqchip/irq-gic-v3-its.c | 5 ++++-
    1 file changed, 4 insertions(+), 1 deletion(-)

    diff --git a/drivers/irqchip/irq-gic-v3-its.c b/drivers/irqchip/irq-gic-v3-its.c
    index d25b7a864bbb..17c15d3b2784 100644
    --- a/drivers/irqchip/irq-gic-v3-its.c
    +++ b/drivers/irqchip/irq-gic-v3-its.c
    @@ -1624,7 +1624,10 @@ static int its_select_cpu(struct irq_data *d,

    cpu = cpumask_pick_least_loaded(d, tmpmask);
    } else {
    - cpumask_and(tmpmask, irq_data_get_affinity_mask(d), cpu_online_mask);
    + cpumask_and(tmpmask, aff_mask, cpu_online_mask);
    + if (cpumask_empty(tmpmask))
    + cpumask_and(tmpmask, irq_data_get_affinity_mask(d),
    + cpu_online_mask);

    /* If we cannot cross sockets, limit the search to that node */
    if ((its_dev->its->flags & ITS_FLAGS_WORKAROUND_CAVIUM_23144) &&
    --
    2.20.1
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