linux-kernel - Re: [PATCH net] net: microchip: lan743x : bidirectional throughuput improvement

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Message-ID: <20231004122016.76b403f0@kernel.org>
Date:   Wed, 4 Oct 2023 12:20:16 -0700
From:   Jakub Kicinski <kuba@...nel.org>
To:     Vishvambar Panth S <vishvambarpanth.s@...rochip.com>
Cc:     <netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>,
        <bryan.whitehead@...rochip.com>, <UNGLinuxDriver@...rochip.com>,
        <davem@...emloft.net>, <edumazet@...gle.com>, <pabeni@...hat.com>,
        <andrew@...n.ch>
Subject: Re: [PATCH net] net: microchip: lan743x : bidirectional throughuput
 improvement

On Wed, 27 Sep 2023 16:46:23 +0530 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)

Nobody complained for 5 years, and it's not a regression.
Let's not treat this as a fix, please repost without the Fixes tag for
net-next.
-- 
pw-bot: cr