linux-kernel - Re: generic DMA bypass flag v4

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Date:   Fri, 10 Jul 2020 15:26:58 +0200
From:   Jesper Dangaard Brouer <brouer@...hat.com>
To:     Christoph Hellwig <hch@....de>
Cc:     iommu@...ts.linux-foundation.org,
        Alexey Kardashevskiy <aik@...abs.ru>,
        linuxppc-dev@...ts.ozlabs.org, Lu Baolu <baolu.lu@...ux.intel.com>,
        Greg Kroah-Hartman <gregkh@...uxfoundation.org>,
        Joerg Roedel <joro@...tes.org>,
        Robin Murphy <robin.murphy@....com>,
        Björn Töpel <bjorn.topel@...il.com>,
        Daniel Borkmann <daniel@...earbox.net>,
        linux-kernel@...r.kernel.org, brouer@...hat.com
Subject: Re: generic DMA bypass flag v4

On Wed,  8 Jul 2020 17:24:44 +0200
Christoph Hellwig <hch@....de> wrote:

> Note that as-is this breaks the XSK buffer pool, which unfortunately
> poked directly into DMA internals.  A fix for that is already queued
> up in the netdev tree.
> 
> Jesper and XDP gang: this should not regress any performance as
> the dma-direct calls are now inlined into the out of line DMA mapping
> calls.  But if you can verify the performance numbers that would be
> greatly appreciated.

From a superficial review of the patches, they look okay to me. I don't
have time to run a performance benchmark (before I go on vacation).

I hoped Björn could test/benchmark this(?), given (as mentioned) this
also affect XSK / AF_XDP performance.

-- 
Best regards,
  Jesper Dangaard Brouer
  MSc.CS, Principal Kernel Engineer at Red Hat
  LinkedIn: http://www.linkedin.com/in/brouer