linux-kernel - Re: [RFC] avoid indirect calls for DMA direct mappings v2

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Message-ID: <20181208165058.GA14874@lst.de>
Date:   Sat, 8 Dec 2018 17:50:58 +0100
From:   Christoph Hellwig <hch@....de>
To:     Jesper Dangaard Brouer <brouer@...hat.com>
Cc:     Christoph Hellwig <hch@....de>, iommu@...ts.linux-foundation.org,
        Linus Torvalds <torvalds@...ux-foundation.org>,
        Tariq Toukan <tariqt@...lanox.com>,
        Ilias Apalodimas <ilias.apalodimas@...aro.org>,
        Toke Høiland-Jørgensen <toke@...e.dk>,
        Robin Murphy <robin.murphy@....com>,
        Konrad Rzeszutek Wilk <konrad.wilk@...cle.com>,
        Tony Luck <tony.luck@...el.com>,
        Fenghua Yu <fenghua.yu@...el.com>,
        Marek Szyprowski <m.szyprowski@...sung.com>,
        Keith Busch <keith.busch@...el.com>,
        Jonathan Derrick <jonathan.derrick@...el.com>,
        linux-pci@...r.kernel.org, linux-ia64@...r.kernel.org,
        x86@...nel.org, linux-kernel@...r.kernel.org
Subject: Re: [RFC] avoid indirect calls for DMA direct mappings v2

On Sat, Dec 08, 2018 at 05:06:48PM +0100, Jesper Dangaard Brouer wrote:
> You can add my:
>  Tested-by: Jesper Dangaard Brouer <brouer@...hat.com>
> or
>  Acked-by: Jesper Dangaard Brouer <brouer@...hat.com>
> 
> I'm very happy that you work on this.  And I've done micro-benchmark
> testing of the patchset (and branch dma-direct-calls), which I've made
> avail here:
>  https://github.com/xdp-project/xdp-project/blob/master/areas/dma/dma01_test_hellwig_direct_dma.org
> 
> My XDP performance is back, minus the BPF-indirect call, and
> net_rx_action napi->poll, and net_device->ndo_xdp_xmit calls.  I
> verified that manually disabling retpoline for these remaining netstack
> retpoline-calls restore the performance full (well minus 1.5 nanosec).

Thanks a lot for all the testing (and the initial report).  I'd love to
still gets this in for 4.21 if we can, but for that I'd need a lot
more folks to carefull review it, especially the swiotlb and ia64 bits.
So if we don't get that early next week I feel we might have to punt
it to the next merge window.