netdev - RE: [Intel-wired-lan] [PATCH net-next v2 2/3] i40e: use 16B HW descriptors instead of 32B

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Message-ID: <DM6PR11MB2890B2527FB513C92041C152BC2A0@DM6PR11MB2890.namprd11.prod.outlook.com>
Date:   Sat, 5 Sep 2020 03:01:08 +0000
From:   "Brown, Aaron F" <aaron.f.brown@...el.com>
To:     Björn Töpel <bjorn.topel@...il.com>,
        "intel-wired-lan@...ts.osuosl.org" <intel-wired-lan@...ts.osuosl.org>
CC:     "netdev@...r.kernel.org" <netdev@...r.kernel.org>,
        "bpf@...r.kernel.org" <bpf@...r.kernel.org>,
        "Topel, Bjorn" <bjorn.topel@...el.com>,
        "Karlsson, Magnus" <magnus.karlsson@...el.com>,
        "kuba@...nel.org" <kuba@...nel.org>
Subject: RE: [Intel-wired-lan] [PATCH net-next v2 2/3] i40e: use 16B HW
 descriptors instead of 32B

> From: Intel-wired-lan <intel-wired-lan-bounces@...osl.org> On Behalf Of
> Björn Töpel
> Sent: Tuesday, August 25, 2020 4:36 AM
> To: intel-wired-lan@...ts.osuosl.org
> Cc: netdev@...r.kernel.org; bpf@...r.kernel.org; Topel, Bjorn
> <bjorn.topel@...el.com>; Karlsson, Magnus <magnus.karlsson@...el.com>;
> kuba@...nel.org
> Subject: [Intel-wired-lan] [PATCH net-next v2 2/3] i40e: use 16B HW
> descriptors instead of 32B
> 
> From: Björn Töpel <bjorn.topel@...el.com>
> 
> The i40e NIC supports two flavors of HW descriptors, 16 and 32
> byte. The latter has, obviously, room for more offloading
> information. However, the only fields of the 32B HW descriptor that is
> being used by the driver, is also available in the 16B descriptor.
> 
> In other words; Reading and writing 32 bytes instead of 16 byte is a
> waste of bus bandwidth.
> 
> This commit starts using 16 byte descriptors instead of 32 byte
> descriptors.
> 
> For AF_XDP the rx_drop benchmark was improved by 2%.
> 
> Signed-off-by: Björn Töpel <bjorn.topel@...el.com>
> ---
>  drivers/net/ethernet/intel/i40e/i40e.h         |  2 +-
>  drivers/net/ethernet/intel/i40e/i40e_debugfs.c | 10 ++++------
>  drivers/net/ethernet/intel/i40e/i40e_main.c    |  4 ++--
>  drivers/net/ethernet/intel/i40e/i40e_trace.h   |  6 +++---
>  drivers/net/ethernet/intel/i40e/i40e_txrx.c    |  6 +++---
>  drivers/net/ethernet/intel/i40e/i40e_txrx.h    |  2 +-
>  drivers/net/ethernet/intel/i40e/i40e_type.h    |  5 ++++-
>  7 files changed, 18 insertions(+), 17 deletions(-)
> 
Tested-by: Aaron Brown <aaron.f.brown@...el.com>