Re: [PATCH net] net: microchip: lan743x : bidirectional throughuput improvement

[VishvambarPanth.S]

On Fri, 2023-09-29 at 10:35 -0700, Jacob Keller wrote:
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> 
> On 9/27/2023 4:16 AM, Vishvambar Panth S wrote:
> > The LAN743x/PCI11xxx DMA descriptors are always 4 dwords long, but
> > the
> > device supports placing the descriptors in memory back to back or
> > reserving space in between them using its DMA_DESCRIPTOR_SPACE
> > (DSPACE)
> > configurable hardware setting. Currently DSPACE is unnecessarily
> > set to
> > match the host's L1 cache line size, resulting in space reserved in
> > between descriptors in most platforms and causing a suboptimal
> > behavior
> > (single PCIe Mem transaction per descriptor). By changing the
> > setting
> > to DSPACE=16 many descriptors can be packed in a single PCIe Mem
> > transaction resulting in a massive performance improvement in
> > bidirectional tests without any negative effects.
> > Tested and verified improvements on x64 PC and several ARM
> > platforms
> > (typical data below)
> > 
> 
> I assume here the choice of 16 is to get the 16 bytes from 4 dwords?

Thanks for the comments. Yes, it is set to 16 bytes to match the size
of the descriptors which are 4 dwords long.
> 
> > Test setup 1: x64 PC with LAN7430 ---> x64 PC
> > 
> > iperf3 UDP bidirectional with DSPACE set to L1 CACHE Size:
> > - - - - - - - - - - - - - - - - - - - - - - - - -
> > [ ID][Role] Interval           Transfer     Bitrate
> > [  5][TX-C]   0.00-10.00  sec   170 MBytes   143 Mbits/sec  sender
> > [  5][TX-C]   0.00-10.04  sec   169 MBytes   141 Mbits/sec 
> > receiver
> > [  7][RX-C]   0.00-10.00  sec  1.02 GBytes   876 Mbits/sec  sender
> > [  7][RX-C]   0.00-10.04  sec  1.02 GBytes   870 Mbits/sec 
> > receiver
> > 
> > iperf3 UDP bidirectional with DSPACE set to 16 Bytes
> > - - - - - - - - - - - - - - - - - - - - - - - - -
> > [ ID][Role] Interval           Transfer     Bitrate
> > [  5][TX-C]   0.00-10.00  sec  1.11 GBytes   956 Mbits/sec  sender
> > [  5][TX-C]   0.00-10.04  sec  1.11 GBytes   951 Mbits/sec 
> > receiver
> > [  7][RX-C]   0.00-10.00  sec  1.10 GBytes   948 Mbits/sec  sender
> > [  7][RX-C]   0.00-10.04  sec  1.10 GBytes   942 Mbits/sec 
> > receiver
> > 
> 
> Going from barely transmitting to hitting the line rate *and*
> improving
> both Tx and Rx slightly is fantastic. Huge win just avoiding all that
> unnecessary wasted PCIe bandwidth.
> 
> > Test setup 2 : RK3399 with LAN7430 ---> x64 PC
> > 
> > RK3399 Spec:
> > The SOM-RK3399 is ARM module designed and developed by
> > FriendlyElec.
> > Cores: 64-bit Dual Core Cortex-A72 + Quad Core Cortex-A53
> > Frequency: Cortex-A72(up to 2.0GHz), Cortex-A53(up to 1.5GHz)
> > PCIe: PCIe x4, compatible with PCIe 2.1, Dual operation mode
> > 
> > iperf3 UDP bidirectional with DSPACE set to L1 CACHE Size:
> > - - - - - - - - - - - - - - - - - - - - - - - - -
> > [ ID][Role] Interval           Transfer     Bitrate
> > [  5][TX-C]   0.00-10.00  sec   534 MBytes   448 Mbits/sec  sender
> > [  5][TX-C]   0.00-10.05  sec   534 MBytes   446 Mbits/sec 
> > receiver
> > [  7][RX-C]   0.00-10.00  sec  1.12 GBytes   961 Mbits/sec  sender
> > [  7][RX-C]   0.00-10.05  sec  1.11 GBytes   946 Mbits/sec 
> > receiver
> > 
> > iperf3 UDP bidirectional with DSPACE set to 16 Bytes
> > - - - - - - - - - - - - - - - - - - - - - - - - -
> > [ ID][Role] Interval           Transfer     Bitrate
> > [  5][TX-C]   0.00-10.00  sec   966 MBytes   810 Mbits/sec   sender
> > [  5][TX-C]   0.00-10.04  sec   965 MBytes   806 Mbits/sec  
> > receiver
> > [  7][RX-C]   0.00-10.00  sec  1.11 GBytes   956 Mbits/sec   sender
> > [  7][RX-C]   0.00-10.04  sec  1.07 GBytes   919 Mbits/sec  
> > receiver
> > 
> > Fixes: 23f0703c125b ("lan743x: Add main source files for new
> > lan743x driver")
> > Signed-off-by: Vishvambar Panth S <vishvambarpanth.s@xxxxxxxxxxxxx>
> > ---
> 
> Always fun to see a massive win like this! Even just the 2x
> improvement
> on the RK3399 is huge, let alone 6x improvement on the x86 platform.
> 
> Reviewed-by: Jacob Keller <jacob.e.keller@xxxxxxxxx>
> 
> >  drivers/net/ethernet/microchip/lan743x_main.h | 2 +-
> >  1 file changed, 1 insertion(+), 1 deletion(-)
> > 
> > diff --git a/drivers/net/ethernet/microchip/lan743x_main.h
> > b/drivers/net/ethernet/microchip/lan743x_main.h
> > index 52609fc13ad9..6dac6fef7d24 100644
> > --- a/drivers/net/ethernet/microchip/lan743x_main.h
> > +++ b/drivers/net/ethernet/microchip/lan743x_main.h
> > @@ -1067,7 +1067,7 @@ struct lan743x_adapter {
> >  #define DMA_DESCRIPTOR_SPACING_32       (32)
> >  #define DMA_DESCRIPTOR_SPACING_64       (64)
> >  #define DMA_DESCRIPTOR_SPACING_128      (128)
> > -#define DEFAULT_DMA_DESCRIPTOR_SPACING  (L1_CACHE_BYTES)
> > +#define DEFAULT_DMA_DESCRIPTOR_SPACING 
> > (DMA_DESCRIPTOR_SPACING_16)
> > 
> >  #define DMAC_CHANNEL_STATE_SET(start_bit, stop_bit) \
> >       (((start_bit) ? 2 : 0) | ((stop_bit) ? 1 : 0))