Re: [RFC PATCH net-next v6 00/15] Device Memory TCP

[Yunsheng Lin]

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?