linux-kernel - Re: [PATCH V2 net 2/9] net: hns3: add sync command to sync io-pgtable

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Message-ID: <5a2786ab-1c7c-4641-a3f6-3c3722f2ac14@huawei.com>
Date: Thu, 24 Oct 2024 17:01:23 +0800
From: Jijie Shao <shaojijie@...wei.com>
To: Paolo Abeni <pabeni@...hat.com>, <davem@...emloft.net>,
	<edumazet@...gle.com>, <kuba@...nel.org>, <shenjian15@...wei.com>,
	<salil.mehta@...wei.com>
CC: <shaojijie@...wei.com>, <liuyonglong@...wei.com>,
	<wangpeiyang1@...wei.com>, <lanhao@...wei.com>, <chenhao418@...wei.com>,
	<netdev@...r.kernel.org>, <linux-kernel@...r.kernel.org>
Subject: Re: [PATCH V2 net 2/9] net: hns3: add sync command to sync io-pgtable


on 2024/10/24 16:36, Paolo Abeni wrote:
> On 10/18/24 12:10, Jijie Shao wrote:
>> From: Jian Shen <shenjian15@...wei.com>
>>
>> To avoid errors in pgtable prefectch, add a sync command to sync
>> io-pagtable.
>>
>> In the case of large traffic, the TX bounce buffer may be used up.
> It's unclear to me what do you mean for large traffic. Is that large
> packets instead?
>
> Skimming over the previous patch, it looks like the for the bugger H/W
> driver will use the bounce buffer for all packets with len < 64K. As
> this driver does not support big tcp, such condition means all packets.
>
> So its not clear to me the 'may' part - it looks like the critical path
> will always happen on the bugged H/W

Sorry, actually not, I mean with tools like iperf3, we can hit the speed limit.
In this case, many packets are sent within a short period of time.
Therefore, the TX bounce buffer may be used up.
In this case, mapping/unmapping is used for packets that cannot use the TX bounce buffer.

Thanks,
Jijie Shao

>
>> At this point, we go to mapping/unmapping on TX path again.
>> So we added the sync command in driver to avoid hardware issue.
> I thought the goal of the previous patch was to avoid such sync-up.
>
> So I don't understand why it's there.
>
> A more verbose explanation will help.
>
>> Signed-off-by: Jian Shen <shenjian15@...wei.com>
>> Signed-off-by: Peiyang Wang <wangpeiyang1@...wei.com>
>> Signed-off-by: Jijie Shao <shaojijie@...wei.com>
> Also we need a fixes tag.
>
> Thanks,
>
> Paolo
>
>