linux-kernel - [PATCH AUTOSEL 5.15 08/10] btrfs: add xxhash to fast checksum implementations

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Message-Id: <20230702194139.1778398-8-sashal@kernel.org>
Date:   Sun,  2 Jul 2023 15:41:37 -0400
From:   Sasha Levin <sashal@...nel.org>
To:     linux-kernel@...r.kernel.org, stable@...r.kernel.org
Cc:     David Sterba <dsterba@...e.com>, Christoph Hellwig <hch@....de>,
        Sasha Levin <sashal@...nel.org>, clm@...com,
        josef@...icpanda.com, linux-btrfs@...r.kernel.org
Subject: [PATCH AUTOSEL 5.15 08/10] btrfs: add xxhash to fast checksum implementations

From: David Sterba <dsterba@...e.com>

[ Upstream commit efcfcbc6a36195c42d98e0ee697baba36da94dc8 ]

The implementation of XXHASH is now CPU only but still fast enough to be
considered for the synchronous checksumming, like non-generic crc32c.

A userspace benchmark comparing it to various implementations (patched
hash-speedtest from btrfs-progs):

  Block size:     4096
  Iterations:     1000000
  Implementation: builtin
  Units:          CPU cycles

	NULL-NOP: cycles:     73384294, cycles/i       73
     NULL-MEMCPY: cycles:    228033868, cycles/i      228,    61664.320 MiB/s
      CRC32C-ref: cycles:  24758559416, cycles/i    24758,      567.950 MiB/s
       CRC32C-NI: cycles:   1194350470, cycles/i     1194,    11773.433 MiB/s
  CRC32C-ADLERSW: cycles:   6150186216, cycles/i     6150,     2286.372 MiB/s
  CRC32C-ADLERHW: cycles:    626979180, cycles/i      626,    22427.453 MiB/s
      CRC32C-PCL: cycles:    466746732, cycles/i      466,    30126.699 MiB/s
	  XXHASH: cycles:    860656400, cycles/i      860,    16338.188 MiB/s

Comparing purely software implementation (ref), current outdated
accelerated using crc32q instruction (NI), optimized implementations by
M. Adler (https://stackoverflow.com/questions/17645167/implementing-sse-4-2s-crc32c-in-software/17646775#17646775)
and the best one that was taken from kernel using the PCLMULQDQ
instruction (PCL).

Reviewed-by: Christoph Hellwig <hch@....de>
Signed-off-by: David Sterba <dsterba@...e.com>
Signed-off-by: Sasha Levin <sashal@...nel.org>
---
 fs/btrfs/disk-io.c | 3 +++
 1 file changed, 3 insertions(+)

diff --git a/fs/btrfs/disk-io.c b/fs/btrfs/disk-io.c
index 3c0b3b4ec5ad5..1fb7cb4492bdb 100644
--- a/fs/btrfs/disk-io.c
+++ b/fs/btrfs/disk-io.c
@@ -2328,6 +2328,9 @@ static int btrfs_init_csum_hash(struct btrfs_fs_info *fs_info, u16 csum_type)
 		if (!strstr(crypto_shash_driver_name(csum_shash), "generic"))
 			set_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags);
 		break;
+	case BTRFS_CSUM_TYPE_XXHASH:
+		set_bit(BTRFS_FS_CSUM_IMPL_FAST, &fs_info->flags);
+		break;
 	default:
 		break;
 	}
-- 
2.39.2