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    SubjectRe: [PATCH 1/3] sfc: revert "reduce the number of requested xdp ev queues"
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    On 07/07/2021 09:16, Íñigo Huguet wrote:
    > The problem is that the TX queues are also contained inside the channel
    > structs, and there are only 4 queues per channel. Reducing the number of
    > channels means also reducing the number of queues, resulting in not
    > having the desired number of 1 queue per CPU.
    >
    > This leads to getting errors on XDP_TX and XDP_REDIRECT if they're
    > executed from a high numbered CPU, because there only exist queues for
    > the low half of CPUs, actually.

    Should we then be using min(tx_per_ev, EFX_MAX_TXQ_PER_CHANNEL) in the
    DIV_ROUND_UP?
    And on line 184 probably we need to set efx->xdp_tx_per_channel to the
    same thing, rather than blindly to EFX_MAX_TXQ_PER_CHANNEL as at
    present — I suspect the issue you mention in patch #2 stemmed from
    that.
    Note that if we are in fact hitting this limitation (i.e. if
    tx_per_ev > EFX_MAX_TXQ_PER_CHANNEL), we could readily increase
    EFX_MAX_TXQ_PER_CHANNEL at the cost of a little host memory, enabling
    us to make more efficient use of our EVQs and thus retain XDP TX
    support up to a higher number of CPUs.

    -ed

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