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Message-ID: <b1f64c44-0d1c-480e-a272-fb017e7d8673@gmail.com>
Date:   Wed, 4 Oct 2023 13:02:17 -0700
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Subject: Re: [PATCH net] net: microchip: lan743x : bidirectional throughuput
 improvement
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To:     Jakub Kicinski <kuba@kernel.org>,
        Vishvambar Panth S <vishvambarpanth.s@microchip.com>
Cc:     netdev@vger.kernel.org, linux-kernel@vger.kernel.org,
        bryan.whitehead@microchip.com, UNGLinuxDriver@microchip.com,
        davem@davemloft.net, edumazet@google.com, pabeni@redhat.com,
        andrew@lunn.ch
References: <20230927111623.9966-1-vishvambarpanth.s@microchip.com>
 <20231004122016.76b403f0@kernel.org>
From:   Florian Fainelli <f.fainelli@gmail.com>
In-Reply-To: <20231004122016.76b403f0@kernel.org>
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On 10/4/23 12:20, Jakub Kicinski wrote:
> 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.

As a driver maintainer, you may want to provide some guarantees to your 
end users/customers that from stable version X.Y.Z the performance 
issues have been fixed. Performance improvements are definitively border 
line in terms of being considered as bug fixes though.
-- 
Florian