linux-kernel - Re: [PATCH net v1 2/2] lan743x: boost performance: limit PCIe bandwidth requirement

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Message-ID: <20201209012218.GN2475764@lunn.ch>
Date:   Wed, 9 Dec 2020 02:22:18 +0100
From:   Andrew Lunn <andrew@...n.ch>
To:     Florian Fainelli <f.fainelli@...il.com>
Cc:     Sven Van Asbroeck <thesven73@...il.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Bryan Whitehead <bryan.whitehead@...rochip.com>,
        Microchip Linux Driver Support <UNGLinuxDriver@...rochip.com>,
        David S Miller <davem@...emloft.net>,
        netdev <netdev@...r.kernel.org>,
        Linux Kernel Mailing List <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net v1 2/2] lan743x: boost performance: limit PCIe
 bandwidth requirement

> dma_sync_single_for_{cpu,device} is what you would need in order to make
> a partial cache line invalidation. You would still need to unmap the
> same address+length pair that was used for the initial mapping otherwise
> the DMA-API debugging will rightfully complain.

But often you don't unmap it, you call dma_sync_single_for_device and
put it back into the ring.

    Andrew