On 2014/11/25 13:30, Liu Bo wrote:
This is actually inspired by ZFS, who offers checksum functions ranging from the simple-and-fast fletcher2 to the slower-but-secure sha256. Back to btrfs, crc32c is the only choice. And also for the slowness of sha256, Intel has a set of instructions for it, "Intel SHA Extensions", that may help a lot.
I think the advantage will be in giving a choice with some strong suggestions:
An example of suggestions - if using sha256 on an old or "low-power" CPU, detect that the CPU doesn't support the appropriate acceleration functions and print a warning at mount or a warning-and-prompt at mkfs-time.
The default could even be changed based on the architecture - though I suspect crc32c is already a good default on most architectures.
The choice allowance gives flexibility where admins know it optimally could be used - and David's suggestion (separate thread) would be able to take advantage of that.
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