linux-kernel - Re: [PATCH] mm/gup_benchmark: update the documentation in Kconfig

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Date:   Thu, 20 Aug 2020 20:51:27 -0700
From:   John Hubbard <jhubbard@...dia.com>
To:     Barry Song <song.bao.hua@...ilicon.com>,
        <akpm@...ux-foundation.org>, <linux-mm@...ck.org>,
        <linux-kselftest@...r.kernel.org>
CC:     <linuxarm@...wei.com>, <linux-kernel@...r.kernel.org>,
        Keith Busch <keith.busch@...el.com>,
        Ira Weiny <ira.weiny@...el.com>,
        "Kirill A . Shutemov" <kirill.shutemov@...ux.intel.com>
Subject: Re: [PATCH] mm/gup_benchmark: update the documentation in Kconfig

On 8/20/20 8:25 PM, Barry Song wrote:
> In the beginning, mm/gup_benchmark.c supported get_user_pages_fast()
> only, but right now, it supports the benchmarking of a couple of
> get_user_pages() related calls like:
> * get_user_pages_fast()
> * get_user_pages()
> * pin_user_pages_fast()
> * pin_user_pages()
> The documentation is confusing and needs update.

hmmm, it's not that confusing, given that pin_user_pages() and
get_user_pages() use the same underlying get_user_pages()
implementation.

> 
> Cc: John Hubbard <jhubbard@...dia.com>
> Cc: Keith Busch <keith.busch@...el.com>
> Cc: Ira Weiny <ira.weiny@...el.com>
> Cc: Kirill A. Shutemov <kirill.shutemov@...ux.intel.com>
> Signed-off-by: Barry Song <song.bao.hua@...ilicon.com>
> ---
>   mm/Kconfig | 4 ++--
>   1 file changed, 2 insertions(+), 2 deletions(-)
> 
> diff --git a/mm/Kconfig b/mm/Kconfig
> index 6c974888f86f..f7c9374da7b3 100644
> --- a/mm/Kconfig
> +++ b/mm/Kconfig
> @@ -831,10 +831,10 @@ config PERCPU_STATS
>   	  be used to help understand percpu memory usage.
>   
>   config GUP_BENCHMARK
> -	bool "Enable infrastructure for get_user_pages_fast() benchmarking"
> +	bool "Enable infrastructure for get_user_pages() and related calls benchmarking"

If we really want to go to the trouble of tweaking this, then I'd go with
something more like:

"Enable infrastructure for get_user_pages() and pin_user_pages benchmarking"

...but I don't think it really warrants a patch just yet. *However*, my
judgment is skewed right now, because I'm planning a small patchset to split
up gup_benchmark a little bit, and to add some more testing and take advantage
of parts of it to do a dump_page() test. At which point "related calls" would
make more sense, but then it would be different enough that this patch would
still need changing.

So I'm inclined to just recommend leaving this alone for a bit, but if others
want to put it in, I'm OK with that too.

>   	help
>   	  Provides /sys/kernel/debug/gup_benchmark that helps with testing
> -	  performance of get_user_pages_fast().
> +	  performance of get_user_pages() and related calls.
>   
>   	  See tools/testing/selftests/vm/gup_benchmark.c
>   
> 

thanks,
-- 
John Hubbard
NVIDIA