linux-kernel - Re: [Intel-wired-lan] [PATCH net-next v5 03/14] page_pool: avoid calling no-op externals when possible

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Date:   Thu, 30 Nov 2023 12:58:27 +0100
From:   Alexander Lobakin <aleksander.lobakin@...el.com>
To:     Yunsheng Lin <linyunsheng@...wei.com>
CC:     Christoph Hellwig <hch@....de>,
        Paul Menzel <pmenzel@...gen.mpg.de>,
        Maciej Fijalkowski <maciej.fijalkowski@...el.com>,
        Jesper Dangaard Brouer <hawk@...nel.org>,
        Larysa Zaremba <larysa.zaremba@...el.com>,
        <netdev@...r.kernel.org>, Alexander Duyck <alexanderduyck@...com>,
        "Ilias Apalodimas" <ilias.apalodimas@...aro.org>,
        <linux-kernel@...r.kernel.org>, Eric Dumazet <edumazet@...gle.com>,
        Michal Kubiak <michal.kubiak@...el.com>,
        <intel-wired-lan@...ts.osuosl.org>,
        David Christensen <drc@...ux.vnet.ibm.com>,
        Jakub Kicinski <kuba@...nel.org>,
        Paolo Abeni <pabeni@...hat.com>,
        "David S. Miller" <davem@...emloft.net>
Subject: Re: [Intel-wired-lan] [PATCH net-next v5 03/14] page_pool: avoid
 calling no-op externals when possible

From: Yunsheng Lin <linyunsheng@...wei.com>
Date: Thu, 30 Nov 2023 16:46:11 +0800

> On 2023/11/29 21:17, Alexander Lobakin wrote:
>> From: Yunsheng Lin <linyunsheng@...wei.com>
>> Date: Wed, 29 Nov 2023 11:17:50 +0800
>>
>>> On 2023/11/27 22:32, Alexander Lobakin wrote:
>>>>
>>>> Chris, any thoughts on a global flag for skipping DMA syncs ladder?
>>>
>>> It seems there was one already in the past:
>>>
>>> https://lore.kernel.org/netdev/7c55a4d7-b4aa-25d4-1917-f6f355bd722e@arm.com/T/
>>
>> It addresses a different problem, meaningless indirect calls, while this
>> one addresses meaningless direct calls :>
>> When the above gets merged, we could combine these two into one global,
>> but Eric wasn't active with his patch and I remember there were some
>> problems, so I wouldn't count on that it will arrive soon.
> 
> I went through the above patch, It seems to me that there was no
> fundamental problem that stopping us from implementing it in the dma
> layer basing on Eric' patch if Eric is no longer interested in working
> on a newer version?

I'm somewhat interested in continuing working on Eric's patch, but not
now. Have some urgent projects to work on, I could take this in January
I guess...
This PP-specific shortcut was done earlier and gives good boosts. It
would be trivial to remove it together with the XSk shortcut once a
generic both indirect and direct call DMA shortcut lands.
Does this sounds good / justified enough? Or you and other
reviewers/maintainers would prefer to wait for the generic one without
taking this patch?

> 
> It is just that if we allow every subsystem and driver using dma API
> doing their own trick of skipping dma sync, then there is less willing
> to implement it in the dma layer.

Thanks,
Olek