linux-kernel - Re: [PATCH v3 09/10] NTB: Add MSI interrupt support to ntb

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Date:   Fri, 22 Mar 2019 11:47:43 -0500
From:   Bjorn Helgaas <helgaas@...nel.org>
To:     Logan Gunthorpe <logang@...tatee.com>
Cc:     linux-kernel@...r.kernel.org, linux-ntb@...glegroups.com,
        linux-pci@...r.kernel.org, iommu@...ts.linux-foundation.org,
        linux-kselftest@...r.kernel.org, Jon Mason <jdmason@...zu.us>,
        Joerg Roedel <joro@...tes.org>,
        Allen Hubbe <allenbh@...il.com>,
        Dave Jiang <dave.jiang@...el.com>,
        Serge Semin <fancer.lancer@...il.com>,
        Eric Pilmore <epilmore@...aio.com>
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

s/set/set,/

> 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

s/recieving/receiving/

> 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/

Bjorn