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Subject: Re: [RFC PATCH net-next v6 00/15] Device Memory TCP
To: Mina Almasry <almasrymina@google.com>, <netdev@vger.kernel.org>,
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References: <20240305020153.2787423-1-almasrymina@google.com>
From: Yunsheng Lin <linyunsheng@huawei.com>
Message-ID: <6208950d-6453-e797-7fc3-1dcf15b49dbe@huawei.com>
Date: Tue, 5 Mar 2024 20:54:42 +0800
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On 2024/3/5 10:01, Mina Almasry wrote:

..

> 
> Perf - page-pool benchmark:
> ---------------------------
> 
> bench_page_pool_simple.ko tests with and without these changes:
> https://pastebin.com/raw/ncHDwAbn
> 
> AFAIK the number that really matters in the perf tests is the
> 'tasklet_page_pool01_fast_path Per elem'. This one measures at about 8
> cycles without the changes but there is some 1 cycle noise in some
> results.
> 
> With the patches this regresses to 9 cycles with the changes but there
> is 1 cycle noise occasionally running this test repeatedly.
> 
> Lastly I tried disable the static_branch_unlikely() in
> netmem_is_net_iov() check. To my surprise disabling the
> static_branch_unlikely() check reduces the fast path back to 8 cycles,
> but the 1 cycle noise remains.
> 

The last sentence seems to be suggesting the above 1 ns regresses is caused
by the static_branch_unlikely() checking?