linux-kernel - Re: [PATCH] lib: test module for find_*

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Date:   Tue, 21 Nov 2017 09:38:27 +0100
From:   Geert Uytterhoeven <geert@...ux-m68k.org>
To:     Yury Norov <ynorov@...iumnetworks.com>
Cc:     "linux-kernel@...r.kernel.org" <linux-kernel@...r.kernel.org>,
        Alexey Dobriyan <adobriyan@...il.com>,
        Andrew Morton <akpm@...ux-foundation.org>,
        Clement Courbet <courbet@...gle.com>,
        Matthew Wilcox <mawilcox@...rosoft.com>,
        Rasmus Villemoes <linux@...musvillemoes.dk>
Subject: Re: [PATCH] lib: test module for find_*_bit() functions

Hi Yury,

On Thu, Nov 9, 2017 at 3:07 PM, Yury Norov <ynorov@...iumnetworks.com> wrote:
> find_bit functions are widely used in the kernel, including hot paths.
> This module tests performance of that functions in 2 typical scenarios:
> randomly filled bitmap with relatively equal distribution of set and
> cleared bits, and sparse bitmap which has 1 set bit for 500 cleared bits.

Thanks for your patch!

> On ThunderX machine:
>
>                  Start testing find_bit() with random-filled bitmap
> [1032111.632383] find_next_bit:         240043 cycles,  164062 iterations
> [1032111.647236] find_next_zero_bit:    312848 cycles,  163619 iterations
> [1032111.661585] find_last_bit:         193748 cycles,  164062 iterations
> [1032113.450517] find_first_bit:        177720874 cycles,       164062 iterations
> [1032113.462930]
>                  Start testing find_bit() with sparse bitmap
> [1032113.477229] find_next_bit:         3633 cycles,    656 iterations
> [1032113.494281] find_next_zero_bit:    620399 cycles,  327025 iterations
> [1032113.506723] find_last_bit:         3038 cycles,    656 iterations
> [1032113.524485] find_first_bit:        691407 cycles,  656 iterations

That's what ends up in dmesg, but that's not what it prints on the console:
"\t" prints an ugly placeholder, as TABs are not supported.

> --- /dev/null
> +++ b/lib/test_find_bit.c
> @@ -0,0 +1,141 @@

> +static int __init test_find_first_bit(void *bitmap, unsigned long len)
> +{
> +       unsigned long i, cnt;
> +       cycles_t cycles;
> +
> +       cycles = get_cycles();

get_cycles() returns zero on half of the architectures.

Gr{oetje,eeting}s,

                        Geert

--
Geert Uytterhoeven -- There's lots of Linux beyond ia32 -- geert@...ux-m68k.org

In personal conversations with technical people, I call myself a hacker. But
when I'm talking to journalists I just say "programmer" or something like that.
                                -- Linus Torvalds