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Date:   Fri, 22 Mar 2019 11:47:43 -0500
From:   Bjorn Helgaas <>
To:     Logan Gunthorpe <>
Cc:,,,,, Jon Mason <>,
        Joerg Roedel <>,
        Allen Hubbe <>,
        Dave Jiang <>,
        Serge Semin <>,
        Eric Pilmore <>
Subject: Re: [PATCH v3 09/10] NTB: Add MSI interrupt support to ntb_transport

Hi Logan,

Drive-by nits:

On Thu, Mar 21, 2019 at 06:06:44PM -0600, Logan Gunthorpe wrote:
> Introduce the module parameter 'use_msi' which, when set uses


> MSI interrupts instead of doorbells for each queue pair (QP). T
> he parameter is only available if NTB MSI support is configured into

Spurious newline in the middle of "The".

> the kernel. We also require there to be more than one memory window
> (MW) so that an extra one is available to forward the APIC region.
> To use MSIs, we request one interrupt per QP and forward the MSI address
> and data to the peer using scratch pad registers (SPADS) above the MW
> spads. (If there are not enough SPADS the MSI interrupt will not be used.)

/spads/SPADS/ for consistency

> Once registered, we simply use ntb_msi_peer_trigger and the recieving


> ISR simply queues up the rxc_db_work for the queue.
> This addition can significantly improve performance of ntb_transport.
> In a simple, untuned, apples-to-apples comparision using ntb_netdev
> and iperf with switchtec hardware, I see 3.88Gb/s without MSI
> interrupts and 14.1Gb/s which is a more than 3x improvement.

s/which is/with MSI, which is/


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