linux-kernel - Re: [PATCH] gfs2: avoid inefficient use of crc32_le

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Message-ID: <CAHc6FU7gs_jg8kkZz7-raHLotx55pn-x3hqqDaiV2cpG5YL_pA@mail.gmail.com>
Date: Sun, 11 May 2025 21:25:41 +0200
From: Andreas Gruenbacher <agruenba@...hat.com>
To: Eric Biggers <ebiggers@...nel.org>
Cc: gfs2@...ts.linux.dev, linux-kernel@...r.kernel.org, 
	Ard Biesheuvel <ardb@...nel.org>
Subject: Re: [PATCH] gfs2: avoid inefficient use of crc32_le_shift()

On Sun, May 11, 2025 at 8:40 PM Eric Biggers <ebiggers@...nel.org> wrote:
> From: Eric Biggers <ebiggers@...gle.com>
>
> __get_log_header() was using crc32_le_shift() to update a CRC with four
> zero bytes.  However, this is about 5x slower than just CRC'ing four
> zero bytes in the normal way.  Just do that instead.
>
> (We could instead make crc32_le_shift() faster on short lengths.  But
> all its callers do just fine without it, so I'd like to just remove it.)
>
> Signed-off-by: Eric Biggers <ebiggers@...gle.com>
> ---
>
> Please consider this patch for the gfs2 tree for 6.16.  If it doesn't
> get picked up, I'll take it through the crc tree.
>
>  fs/gfs2/recovery.c | 3 ++-
>  1 file changed, 2 insertions(+), 1 deletion(-)
>
> diff --git a/fs/gfs2/recovery.c b/fs/gfs2/recovery.c
> index f4fe7039f725b..9080f1b5f434d 100644
> --- a/fs/gfs2/recovery.c
> +++ b/fs/gfs2/recovery.c
> @@ -116,19 +116,20 @@ void gfs2_revoke_clean(struct gfs2_jdesc *jd)
>  }
>
>  int __get_log_header(struct gfs2_sbd *sdp, const struct gfs2_log_header *lh,
>                      unsigned int blkno, struct gfs2_log_header_host *head)
>  {
> +       const u32 zero = 0;
>         u32 hash, crc;
>
>         if (lh->lh_header.mh_magic != cpu_to_be32(GFS2_MAGIC) ||
>             lh->lh_header.mh_type != cpu_to_be32(GFS2_METATYPE_LH) ||
>             (blkno && be32_to_cpu(lh->lh_blkno) != blkno))
>                 return 1;
>
>         hash = crc32(~0, lh, LH_V1_SIZE - 4);
> -       hash = ~crc32_le_shift(hash, 4); /* assume lh_hash is zero */
> +       hash = ~crc32(hash, &zero, 4); /* assume lh_hash is zero */
>
>         if (be32_to_cpu(lh->lh_hash) != hash)
>                 return 1;
>
>         crc = crc32c(~0, (void *)lh + LH_V1_SIZE + 4,
>
> base-commit: 3ce9925823c7d6bb0e6eb951bf2db0e9e182582d
> --
> 2.49.0
>

Applied to for-next.

Thanks,
Andreas