Re: [Qemu-devel] [RFC PATCH qemu] qapi: Add query-memory-checksum

[Daniel P . Berrangé]

On Fri, Aug 23, 2019 at 07:49:31AM +0200, Markus Armbruster wrote:
> Daniel P. Berrangé <address@hidden> writes:
> 
> > On Thu, Aug 22, 2019 at 04:16:53PM +0200, Markus Armbruster wrote:
> >> Alexey Kardashevskiy <address@hidden> 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 <address@hidden>
> >> 
> >> 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.
> 
> Good points.
> 
> The doc strings should spell out "for debugging", like the commit
> message does, and both should spell out "weak collision resistance".
> 
> I can't find CRC-32 in GLib, but zlib appears to provide it:
> http://refspecs.linuxbase.org/LSB_3.0.0/LSB-Core-generic/LSB-Core-generic/zlib-crc32-1.html
> 
> Care to compare its speed to MD5?

I hacked the code to use zlib's crc32 impl and got these for comparison:

/crypto/hash/crc32/speed-512: 1089.18 MB/sec OK
/crypto/hash/crc32/speed-1024: 1124.63 MB/sec OK
/crypto/hash/crc32/speed-4096: 1162.73 MB/sec OK
/crypto/hash/crc32/speed-16384: 1171.58 MB/sec OK
/crypto/hash/crc32/speed-1048576: 1165.68 MB/sec OK
/crypto/hash/md5/speed-512: 476.27 MB/sec OK
/crypto/hash/md5/speed-1024: 517.16 MB/sec OK
/crypto/hash/md5/speed-4096: 554.70 MB/sec OK
/crypto/hash/md5/speed-16384: 564.44 MB/sec OK
/crypto/hash/md5/speed-1048576: 566.78 MB/sec OK


Regards,
Daniel
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