On 7.10.19 г. 12:11 ч., Johannes Thumshirn wrote:
> This series adds support for two additional checksum algorithms to btrfs.
> These
> algorithms are xxhash64[1] and sha256[2].
>
> xxhash64 is a fast non-cryptographic hash function with good collision
> resistance.
> It has a constant output length of 8 Byte (64 Bit), it provides a good
> trade-off between collision resistance and speed compared to the currently
> used crc32c.
>
> sha256 is the 32 Byte (256 Bit) variant of the SHA-2 cryptographic hash. It
> provides cryptographically secure collision resistance with a trade off in
> speed.
>
> Support for xxhash64 in mkfs.btrfs is in the current devel branch and sha256
> support will be sent separately after this patch-set.
>
> In addition to adding these two hash algorithms two sysfs files are
> implemented, one being /sys/fs/btrfs/features/supported_checksums showing the
> in kernel support for different checksumming algorithms. The other one is
> /sys/fs/btrfs/$FSID/checksum showing the checksum used for a specific
> file-system and the used in-kernel driver for this checksum.
>
> Here is an example in a qemu vm:
> host:/# cat /sys/fs/btrfs/features/supported_checksums
> crc32c, xxhash64, sha256
> host:/# cat /sys/fs/btrfs/3cf09516-5bb8-498f-834d-e9ec54043546/checksum
> sha256 (sha256-generic)
>
> This series has survived the usual regression testing with xfstests.
>
> I could not observe any performance differences between any of these hashes in
> my test setup 256K mixed read-write IO to a single file from a single process
> on both a 5700rpm SATA 3G Disk behind a HPE SmartArray RAID HBA and RAM Disk.
>
> Here's the raw numbers for the spinning rust behind SATA:
> CRC32C Buffered Read (KiB/s): Avg: 7881, Min: 7495, Max: 8744, Stdev: 508
> CRC32C Buffered Write (KiB/s): Avg: 7883, Min: 7497, Max: 8746, Stdev: 508
>
> CRC32C Direct Read (KiB/s): Avg: 331, Min: 319, Max: 339, Stdev: 7
> CRC32C Direct Write (KiB/s): Avg: 331, Min: 319, Max: 339, Stdev: 7
>
> XXHASH64 Buffered Read (KiB/s): Avg: 8143, Min: 7748, Max: 8721, Stdev: 355
> XXHASH64 Buffered Write (KiB/s): Avg: 8145, Min: 7750, Max: 8722, Stdev: 355
>
> XXHASH64 Direct Read (KiB/s): Avg: 311, Min: 248, Max: 336, Stdev: 36
> XXHASH64 Direct Write (KiB/s): Avg: 311, Min: 248, Max: 336, Stdev: 36
>
> SHA256 Buffered Read (KiB/s): Avg: 7997, Min: 7665, Max: 8336, Stdev: 273
> SHA256 Buffered Write (KiB/s): Avg: 7998, Min: 7666, Max: 8337, Stdev: 273
>
> SHA256 Direct Read (KiB/s): Avg: 312, Min: 248, Max: 336, Stdev: 36
> SHA256 Direct Write (KiB/s): Avg: 312, Min: 248, Max: 336, Stdev: 36
>
> The reason I could not observe any changes in performance is the fact that the
> btrfs checksumming process takes only 0.04% of the IO path. This also explains
> the very small standard deviation in the above table as I stooped benchmarking
> after 5 benchmark runs.
>
> The hottest call chain (according to perf) is this:
>
> 17.08% 0.00% kworker/u128:9- [kernel.vmlinux] [k]
> btrfs_finish_ordered_io
> |
> ---btrfs_finish_ordered_io
> |
> --17.04%--insert_reserved_file_extent.constprop.75
> |
> --17.02%--__btrfs_drop_extents
> |
> --16.94%--btrfs_free_extent
> |
> --16.94%--btrfs_add_delayed_data_ref
> |
> --16.90%--btrfs_qgroup_trace_extent_post
Yeah, we know qgroups tracing and backrefs resolv are somewhat slow. How
about benchmarking without them since I believe this to be more
representative of how people use btrfs.
> btrfs_find_all_roots
> |
> --16.90%--btrfs_find_all_roots_safe
> |
> --16.89%--find_parent_nodes
> |
> --16.68%--resolve_indirect_refs
> [snip]
>
> [1] https://cyan4973.github.io/xxHash
> [2] https://en.wikipedia.org/wiki/SHA-2
>
> David Sterba (1):
> btrfs: sysfs: export supported checksums
>
> Johannes Thumshirn (3):
> btrfs: add xxhash64 to checksumming algorithms
> btrfs: add sha256 to checksumming algorithms
> btrfs: show used checksum driver per filesystem in sysfs
>
> fs/btrfs/Kconfig | 2 ++
> fs/btrfs/ctree.c | 7 ++++++
> fs/btrfs/ctree.h | 2 ++
> fs/btrfs/disk-io.c | 2 ++
> fs/btrfs/super.c | 2 ++
> fs/btrfs/sysfs.c | 48
> +++++++++++++++++++++++++++++++++++++++++
> include/uapi/linux/btrfs_tree.h | 2 ++
> 7 files changed, 65 insertions(+)
>
