linux-kernel - Re: [PATCH net-next v2 0/2] net: mvneta: improve rx performance

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Date:   Fri, 17 Feb 2017 18:09:33 +0800
From:   Jisheng Zhang <jszhang@...vell.com>
To:     <thomas.petazzoni@...e-electrons.com>, <davem@...emloft.net>,
        <arnd@...db.de>
CC:     <linux-arm-kernel@...ts.infradead.org>, <netdev@...r.kernel.org>,
        <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH net-next v2 0/2] net: mvneta: improve rx performance

On Fri, 17 Feb 2017 18:02:31 +0800
Jisheng Zhang <jszhang@...vell.com> wrote:

> In hot code path such as mvneta_rx_hwbm() and mvneta_rx_swbm(), we may
> access fields of rx_desc. The rx_desc is allocated by
> dma_alloc_coherent, it's uncacheable if the device isn't cache
> coherent, reading from uncached memory is fairly slow.
> 
> patch1 reuses the read out status to getting status field of rx_desc
> again.
> 
> patch2 uses cacheable memory to store the rx buffer DMA address.
> 
> We get the following performance data on Marvell BG4CT Platforms
> (tested with iperf):
> 
> before the patch:
> recving 1GB in mvneta_rx_swbm() costs 149265960 ns

oops, I still didn't correct the typo here, it should be 1492659600 ns

Sorry, but I think there must be comments, I'll fix this typo in v3 when
address comments.

> 
> after the patch:
> recving 1GB in mvneta_rx_swbm() costs 1421565640 ns
> 
> We saved 4.76% time.
> 
> RFC: can we do similar modification for tx? If yes, I can prepare a v2.
> 
> 
> Basically, these two patches do what Arnd mentioned in [1].
> 
> Hi Arnd,
> 
> I added "Suggested-by you" tag, I hope you don't mind ;)
> 
> Thanks
> 
> [1] https://www.spinics.net/lists/netdev/msg405889.html
> 
> Since v1:
>   - correct the performance data typo
> 
> Jisheng Zhang (2):
>   net: mvneta: avoid getting status from rx_desc as much as possible
>   net: mvneta: Use cacheable memory to store the rx buffer DMA address
> 
>  drivers/net/ethernet/marvell/mvneta.c | 36 ++++++++++++++++++++---------------
>  1 file changed, 21 insertions(+), 15 deletions(-)
>