netdev - Re: [PATCH V2 net 4/4] net: hns3: default enable tx bounce buffer when smmu enabled

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Message-ID: <20250723072900.GV2459@horms.kernel.org>
Date: Wed, 23 Jul 2025 08:29:00 +0100
From: Simon Horman <horms@...nel.org>
To: Jijie Shao <shaojijie@...wei.com>
Cc: davem@...emloft.net, edumazet@...gle.com, kuba@...nel.org,
	pabeni@...hat.com, andrew+netdev@...n.ch, shenjian15@...wei.com,
	liuyonglong@...wei.com, chenhao418@...wei.com,
	jonathan.cameron@...wei.com, shameerali.kolothum.thodi@...wei.com,
	salil.mehta@...wei.com, netdev@...r.kernel.org,
	linux-kernel@...r.kernel.org
Subject: Re: [PATCH V2 net 4/4] net: hns3: default enable tx bounce buffer
 when smmu enabled

On Tue, Jul 22, 2025 at 08:54:23PM +0800, Jijie Shao wrote:
> The SMMU engine on HIP09 chip has a hardware issue.
> SMMU pagetable prefetch features may prefetch and use a invalid PTE
> even the PTE is valid at that time. This will cause the device trigger
> fake pagefaults. The solution is to avoid prefetching by adding a
> SYNC command when smmu mapping a iova. But the performance of nic has a
> sharp drop. Then we do this workaround, always enable tx bounce buffer,
> avoid mapping/unmapping on TX path.
> 
> This issue only affects HNS3, so we always enable
> tx bounce buffer when smmu enabled to improve performance.
> 
> Fixes: 295ba232a8c3 ("net: hns3: add device version to replace pci revision")
> Signed-off-by: Jian Shen <shenjian15@...wei.com>
> Signed-off-by: Jijie Shao <shaojijie@...wei.com>
> ---
> ChangeLog:
> v1 -> v2:
>   - Split this patch, omits the ethtool changes,
>     ethtool changes will be sent to net-next, suggested by Simon Horman
>   v1: https://lore.kernel.org/all/20250702130901.2879031-1-shaojijie@huawei.com/

Thanks for breaking this out.

Reviewed-by: Simon Horman <horms@...nel.org>