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

Sasha Levin
2023-07-02T19:45:19Z

From: David Sterba <dsterba@suse.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Comparing purely software implementation (ref), current outdated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@lst.de>
Signed-off-by: David Sterba <dsterba@suse.com>
Signed-off-by: Sasha Levin <sashal@kernel.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