linux-kernel - Re: [PATCH 1/4] net: thunderx: Fix IOMMU translation faults

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Date:   Mon, 6 Mar 2017 18:27:52 +0530
From:   Sunil Kovvuri <sunil.kovvuri@...il.com>
To:     Robin Murphy <robin.murphy@....com>
Cc:     David Miller <davem@...emloft.net>,
        Linux Netdev List <netdev@...r.kernel.org>,
        Sunil Goutham <sgoutham@...ium.com>,
        LKML <linux-kernel@...r.kernel.org>,
        LAKML <linux-arm-kernel@...ts.infradead.org>
Subject: Re: [PATCH 1/4] net: thunderx: Fix IOMMU translation faults

>>
>> We are seeing a 0.75Mpps drop with IP forwarding rate due to that.
>> Hence I have restricted calling DMA interfaces to only when IOMMU is enabled.
>
> What's 0.07Mpps as a percentage of baseline? On a correctly configured
> coherent arm64 system, in the absence of an IOMMU, dma_map_*() is
> essentially just virt_to_phys() behind a function call or two, so I'd be
> interested to know where any non-trivial overhead might be coming from.

It's a 5% drop and yes device is configured as coherent.
And the drop is due to additional function calls.

Thanks,
Sunil.