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

From: Alexander Lobakin <aleksander.lobakin@intel.com>
To: Yunsheng Lin <linyunsheng@huawei.com>
Cc: Paul Menzel <pmenzel@molgen.mpg.de>,
	Maciej Fijalkowski <maciej.fijalkowski@intel.com>,
	Jesper Dangaard Brouer <hawk@kernel.org>,
	Larysa Zaremba <larysa.zaremba@intel.com>,
	netdev@vger.kernel.org, Alexander Duyck <alexanderduyck@fb.com>,
	Ilias Apalodimas <ilias.apalodimas@linaro.org>,
	linux-kernel@vger.kernel.org,
	"David S. Miller" <davem@davemloft.net>,
	Eric Dumazet <edumazet@google.com>,
	Michal Kubiak <michal.kubiak@intel.com>,
	intel-wired-lan@lists.osuosl.org,
	David Christensen <drc@linux.vnet.ibm.com>,
	Jakub Kicinski <kuba@kernel.org>, Paolo Abeni <pabeni@redhat.com>,
	Christoph Hellwig <hch@lst.de>
Subject: Re: [Intel-wired-lan] [PATCH net-next v5 03/14] page_pool: avoid calling no-op externals when possible
Date: Thu, 30 Nov 2023 12:58:27 +0100	[thread overview]
Message-ID: <d8631d76-4bb3-41a4-a2b2-86725867d2a9@intel.com> (raw)
In-Reply-To: <4814a337-454b-d476-dabe-5035dd6dc51f@huawei.com>

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

> On 2023/11/29 21:17, Alexander Lobakin wrote:
>> From: Yunsheng Lin <linyunsheng@huawei.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
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