On Thu, Aug 22, 2019 at 04:16:53PM +0200, Markus Armbruster wrote: > Alexey Kardashevskiy <a...@ozlabs.ru> writes: > > > This returns MD5 checksum of all RAM blocks for migration debugging > > as this is way faster than saving the entire RAM to a file and checking > > that. > > > > Signed-off-by: Alexey Kardashevskiy <a...@ozlabs.ru> > > Any particular reason for MD5? Have you measured the other choices > offered by GLib? > > I understand you don't need crypto-strength here. Both MD5 and SHA-1 > would be bad choices then.
We have a tests/bench-crypto-hash test but its hardcoded for sha256. I hacked it to report all algorithms and got these results for varying input chunk sizes: /crypto/hash/md5/speed-512: 519.12 MB/sec OK /crypto/hash/md5/speed-1024: 560.39 MB/sec OK /crypto/hash/md5/speed-4096: 591.39 MB/sec OK /crypto/hash/md5/speed-16384: 576.46 MB/sec OK /crypto/hash/sha1/speed-512: 443.12 MB/sec OK /crypto/hash/sha1/speed-1024: 518.82 MB/sec OK /crypto/hash/sha1/speed-4096: 555.60 MB/sec OK /crypto/hash/sha1/speed-16384: 568.16 MB/sec OK /crypto/hash/sha224/speed-512: 221.90 MB/sec OK /crypto/hash/sha224/speed-1024: 239.79 MB/sec OK /crypto/hash/sha224/speed-4096: 269.37 MB/sec OK /crypto/hash/sha224/speed-16384: 274.87 MB/sec OK /crypto/hash/sha256/speed-512: 222.75 MB/sec OK /crypto/hash/sha256/speed-1024: 253.25 MB/sec OK /crypto/hash/sha256/speed-4096: 272.80 MB/sec OK /crypto/hash/sha256/speed-16384: 275.59 MB/sec OK /crypto/hash/sha384/speed-512: 322.73 MB/sec OK /crypto/hash/sha384/speed-1024: 369.84 MB/sec OK /crypto/hash/sha384/speed-4096: 406.71 MB/sec OK /crypto/hash/sha384/speed-16384: 417.87 MB/sec OK /crypto/hash/sha512/speed-512: 320.62 MB/sec OK /crypto/hash/sha512/speed-1024: 361.93 MB/sec OK /crypto/hash/sha512/speed-4096: 404.91 MB/sec OK /crypto/hash/sha512/speed-16384: 418.53 MB/sec OK /crypto/hash/ripemd160/speed-512: 226.45 MB/sec OK /crypto/hash/ripemd160/speed-1024: 239.25 MB/sec OK /crypto/hash/ripemd160/speed-4096: 251.31 MB/sec OK /crypto/hash/ripemd160/speed-16384: 255.01 MB/sec OK IOW, md5 is clearly the quickest, by a considerable margin over SHA256/512. SHA1 is slightly slower. Assuming that we document that this command is intentionally *not* trying to guarantee collision resistances we're ok. In fact we should not document what kind of checksum is reported by query-memory-checksum. The impl should be a black box from user's POV. If we're just aiming for debugging tool to detect accidental corruption, could we even just ignore cryptographic hashs entirely and do a crc32 - that'd be way faster than even md5. Regards, Daniel -- |: https://berrange.com -o- https://www.flickr.com/photos/dberrange :| |: https://libvirt.org -o- https://fstop138.berrange.com :| |: https://entangle-photo.org -o- https://www.instagram.com/dberrange :|
