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From: Kent Overstreet <kent.overstreet@linux.dev>
To: Kuan-Wei Chiu <visitorckw@gmail.com>
Cc: colyli@suse.de, bfoster@redhat.com, jserv@ccns.ncku.edu.tw,
	 linux-bcache@vger.kernel.org, linux-kernel@vger.kernel.org,
	linux-bcachefs@vger.kernel.org
Subject: Re: [PATCH 2/5] bcachefs: Introduce parent function for sort_cmp_size()
Date: Sun, 21 Jan 2024 11:17:30 -0500	[thread overview]
Message-ID: <vrzgjxym2gnawuds54s4lr4zqbldm6sxp5yksrz5467hcrzjtp@lphbsqbidqdm> (raw)
In-Reply-To: <20240121153649.2733274-3-visitorckw@gmail.com>

On Sun, Jan 21, 2024 at 11:36:46PM +0800, Kuan-Wei Chiu wrote:
> When dealing with array indices, the parent's index can be obtained
> using the formula (i - 1) / 2. However, when working with byte offsets,
> this approach is not straightforward. To address this, we have
> introduced a branch-free parent function that does not require any
> division operations to calculate the parent's byte offset.

This is a good commit message - but it would be even better if it was a
function comment on parent()

> 
> Signed-off-by: Kuan-Wei Chiu <visitorckw@gmail.com>
> ---
> This patch has undergone unit testing using the following code [1].
> 
> [1]:
> static int test(void)
> {
>     size_t i, p, size, lsbit;
> 
>     for (i = 0; i < 10000; i++) {
>         size = get_random_u32() % (1U << 10);
>         lsbit = size & -size;
>         i = get_random_u32() % (1U << 20) * size + size;
>         p = parent(i, lsbit, size);
>         if (p != (i / size - 1) / 2 * size)
>             return -1;
>     }
> 
>     return 0;
> }
> 
>  fs/bcachefs/util.c | 7 +++++++
>  1 file changed, 7 insertions(+)
> 
> diff --git a/fs/bcachefs/util.c b/fs/bcachefs/util.c
> index bbc83b43162e..f5bbf96df2ce 100644
> --- a/fs/bcachefs/util.c
> +++ b/fs/bcachefs/util.c
> @@ -907,6 +907,13 @@ static inline void do_swap(void *base, size_t n, size_t size,
>  		  size);
>  }
>  
> +static inline size_t parent(size_t i, size_t lsbit, size_t size)
> +{
> +	i -= size;
> +	i -= size & -(i & lsbit);
> +	return i >> 1;
> +}
> +
>  void eytzinger0_sort(void *base, size_t n, size_t size,
>  		     int (*cmp_func)(const void *, const void *, size_t),
>  		     void (*swap_func)(void *, void *, size_t))
> -- 
> 2.25.1
> 

  reply	other threads:[~2024-01-21 16:17 UTC|newest]

Thread overview: 15+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2024-01-21 15:36 [PATCH 0/5] Optimize number of comparisons for heap/heapsort implementaion Kuan-Wei Chiu
2024-01-21 15:36 ` [PATCH 1/5] bcachefs: Optimize eytzinger0_sort() using bottom-up heapsort Kuan-Wei Chiu
2024-01-21 15:36 ` [PATCH 2/5] bcachefs: Introduce parent function for sort_cmp_size() Kuan-Wei Chiu
2024-01-21 16:17   ` Kent Overstreet [this message]
2024-01-21 17:05     ` Kuan-Wei Chiu
2024-01-21 17:37       ` Kent Overstreet
2024-01-21 15:36 ` [PATCH 3/5] bcachefs: Optimize sort_cmp_size() using bottom-up heapsort Kuan-Wei Chiu
2024-01-21 15:36 ` [PATCH 4/5] bcachefs: Optimize number of comparisons in heap_sift_down Kuan-Wei Chiu
2024-01-21 15:36 ` [PATCH 5/5] bcache: Optimize number of comparisons in heap_sift Kuan-Wei Chiu
2024-01-21 16:21 ` [PATCH 0/5] Optimize number of comparisons for heap/heapsort implementaion Kent Overstreet
2024-01-21 16:55   ` Kuan-Wei Chiu
2024-01-21 17:41     ` Kent Overstreet
2024-01-22 15:06       ` Kuan-Wei Chiu
2024-01-22 16:06         ` Kent Overstreet
2024-01-22 16:23           ` Kuan-Wei Chiu

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