tailscale

Commit Graph

Author	SHA1	Message	Date
slowy07	ac0353e982	fix: typo spelling grammar Signed-off-by: slowy07 <slowy.arfy@gmail.com>	3 years ago
Joe Tsai	9d0c86b6ec	util/deephash: remove unnecessary formatting for structs and slices (#2571 ) The index for every struct field or slice element and the number of fields for the struct is unncessary. The hashing of Go values is unambiguous because every type (except maps) encodes in a parsable manner. So long as we know the type information, we could theoretically decode every value (except for maps). At a high level: * numbers are encoded as fixed-width records according to precision. * strings (and AppendTo output) are encoded with a fixed-width length, followed by the contents of the buffer. * slices are prefixed by a fixed-width length, followed by the encoding of each value. So long as we know the type of each element, we could theoretically decode each element. * arrays are encoded just like slices, but elide the length since it is determined from the Go type. * maps are encoded first with a byte indicating whether it is a cycle. If a cycle, it is followed by a fixed-width index for the pointer, otherwise followed by the SHA-256 hash of its contents. The encoding of maps is not decodeable, but a SHA-256 hash is sufficient to avoid ambiguities. * interfaces are encoded first with a byte indicating whether it is nil. If not nil, it is followed by a fixed-width index for the type, and then the encoding for the underlying value. Having the type be encoded first ensures that the value could theoretically be decoded next. * pointers are encoded first with a byte indicating whether it is 1) nil, 2) a cycle, or 3) newly seen. If a cycle, it is followed by a fixed-width index for the pointer. If newly seen, it is followed by the encoding for the pointed-at value. Removing unnecessary details speeds up hashing: name old time/op new time/op delta Hash-8 76.0µs ± 1% 55.8µs ± 2% -26.62% (p=0.000 n=10+10) HashMapAcyclic-8 61.9µs ± 0% 62.0µs ± 0% ~ (p=0.666 n=9+9) TailcfgNode-8 10.2µs ± 1% 7.5µs ± 1% -26.90% (p=0.000 n=10+9) HashArray-8 1.07µs ± 1% 0.70µs ± 1% -34.67% (p=0.000 n=10+9) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	d8fbce7eef	util/deephash: hash uint{8,16,32,64} explicitly (#2502 ) Instead of hashing the humanly formatted forms of a number, hash the native machine bits of the integers themselves. There is a small performance gain for this: name old time/op new time/op delta Hash-8 75.7µs ± 1% 76.0µs ± 2% ~ (p=0.315 n=10+9) HashMapAcyclic-8 63.1µs ± 3% 61.3µs ± 1% -2.77% (p=0.000 n=10+10) TailcfgNode-8 10.3µs ± 1% 10.2µs ± 1% -1.48% (p=0.000 n=10+10) HashArray-8 1.07µs ± 1% 1.05µs ± 1% -1.79% (p=0.000 n=10+10) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	01d4dd331d	util/deephash: simplify hasher.hashMap (#2503 ) The swapping of bufio.Writer between hasher and mapHasher is subtle. Just embed a hasher in mapHasher to avoid complexity here. No notable change in performance: name old time/op new time/op delta Hash-8 76.7µs ± 1% 77.0µs ± 1% ~ (p=0.182 n=9+10) HashMapAcyclic-8 62.4µs ± 1% 62.5µs ± 1% ~ (p=0.315 n=10+9) TailcfgNode-8 10.3µs ± 1% 10.3µs ± 1% -0.62% (p=0.004 n=10+9) HashArray-8 1.07µs ± 1% 1.06µs ± 1% -0.98% (p=0.001 n=8+9) Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	d145c594ad	util/deephash: improve cycle detection (#2470 ) The previous algorithm used a map of all visited pointers. The strength of this approach is that it quickly prunes any nodes that we have ever visited before. The detriment of the approach is that pruning is heavily dependent on the order that pointers were visited. This is especially relevant for hashing a map where map entries are visited in a non-deterministic manner, which would cause the map hash to be non-deterministic (which defeats the point of a hash). This new algorithm uses a stack of all visited pointers, similar to how github.com/google/go-cmp performs cycle detection. When we visit a pointer, we push it onto the stack, and when we leave a pointer, we pop it from the stack. Before visiting a pointer, we first check whether the pointer exists anywhere in the stack. If yes, then we prune the node. The detriment of this approach is that we may hash a node more often than before since we do not prune as aggressively. The set of visited pointers up until any node is only the path of nodes up to that node and not any other pointers that may have been visited elsewhere. This provides us deterministic hashing regardless of visit order. We can now delete hashMapFallback and associated complexity, which only exists because the previous approach was non-deterministic in the presence of cycles. This fixes a failure of the old algorithm where obviously different values are treated as equal because the pruning was too aggresive. See https://github.com/tailscale/tailscale/issues/2443#issuecomment-883653534 The new algorithm is slightly slower since it prunes less aggresively: name old time/op new time/op delta Hash-8 66.1µs ± 1% 68.8µs ± 1% +4.09% (p=0.000 n=19+19) HashMapAcyclic-8 63.0µs ± 1% 62.5µs ± 1% -0.76% (p=0.000 n=18+19) TailcfgNode-8 9.79µs ± 2% 9.88µs ± 1% +0.95% (p=0.000 n=19+17) HashArray-8 643ns ± 1% 653ns ± 1% +1.64% (p=0.000 n=19+19) However, a slower but more correct algorithm seems more favorable than a faster but incorrect algorithm. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	d666bd8533	util/deephash: disambiguate hashing of AppendTo (#2483 ) Prepend size to AppendTo output. Fixes #2443 Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	23ad028414	util/deephash: include type as part of hash for interfaces (#2476 ) A Go interface may hold any number of different concrete types. Just because two underlying values hash to the same thing does not mean the two values are identical if they have different concrete types. As such, include the type in the hash.	3 years ago
Joe Tsai	a5fb8e0731	util/deephash: introduce deliberate instability (#2477 ) Seed the hash upon first use with the current time. This ensures that the stability of the hash is bounded within the lifetime of one program execution. Hopefully, this prevents future bugs where someone assumes that this hash is stable. Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Joe Tsai	9a0c8bdd20	util/deephash: make hash type opaque The fact that Hash returns a [sha256.Size]byte leaks details about the underlying hash implementation. This could very well be any other hashing algorithm with a possible different block size. Abstract this implementation detail away by declaring an opaque type that is comparable. While we are changing the signature of UpdateHash, rename it to just Update to reduce stutter (e.g., deephash.Update). Signed-off-by: Joe Tsai <joetsai@digital-static.net>	3 years ago
Brad Fitzpatrick	ddb8726c98	util/deephash: don't reflect.Copy if element type is a defined uint8 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	3 years ago
Brad Fitzpatrick	6dc38ff25c	util/deephash: optimize hashing of byte arrays, reduce allocs in Hash name old time/op new time/op delta Hash-6 173µs ± 4% 101µs ± 3% -41.69% (p=0.000 n=10+9) HashMapAcyclic-6 101µs ± 5% 105µs ± 3% +3.52% (p=0.001 n=9+10) TailcfgNode-6 29.4µs ± 2% 16.4µs ± 3% -44.25% (p=0.000 n=8+10) name old alloc/op new alloc/op delta Hash-6 3.60kB ± 0% 1.13kB ± 0% -68.70% (p=0.000 n=10+10) HashMapAcyclic-6 2.53kB ± 0% 2.53kB ± 0% ~ (p=0.137 n=10+8) TailcfgNode-6 528B ± 0% 0B -100.00% (p=0.000 n=10+10) name old allocs/op new allocs/op delta Hash-6 84.0 ± 0% 40.0 ± 0% -52.38% (p=0.000 n=10+10) HashMapAcyclic-6 202 ± 0% 202 ± 0% ~ (all equal) TailcfgNode-6 11.0 ± 0% 0.0 -100.00% (p=0.000 n=10+10) Updates tailscale/corp#2130 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	3 years ago
Brad Fitzpatrick	3962744450	util/deephash: prevent infinite loop on map cycle Fixes #2340 Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	3 years ago
Brad Fitzpatrick	aceaa70b16	util/deephash: move funcs to methods Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	3 years ago
Brad Fitzpatrick	14f901da6d	util/deephash: fix sync.Pool usage Whoops. From yesterday's `9ae3bd0939` (not yet used by anything, fortunately) Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	3 years ago
Brad Fitzpatrick	bf9f279768	util/deephash: optimize CPU a bit by by avoiding fmt in more places name old time/op new time/op delta Hash-6 179µs ± 5% 173µs ± 4% -3.12% (p=0.004 n=10+10) HashMapAcyclic-6 115µs ± 3% 101µs ± 5% -11.51% (p=0.000 n=9+9) TailcfgNode-6 30.8µs ± 4% 29.4µs ± 2% -4.51% (p=0.000 n=10+8) name old alloc/op new alloc/op delta Hash-6 3.60kB ± 0% 3.60kB ± 0% ~ (p=0.445 n=9+10) HashMapAcyclic-6 2.53kB ± 0% 2.53kB ± 0% ~ (p=0.065 n=9+10) TailcfgNode-6 528B ± 0% 528B ± 0% ~ (all equal) name old allocs/op new allocs/op delta Hash-6 84.0 ± 0% 84.0 ± 0% ~ (all equal) HashMapAcyclic-6 202 ± 0% 202 ± 0% ~ (all equal) TailcfgNode-6 11.0 ± 0% 11.0 ± 0% ~ (all equal) Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	3 years ago
Brad Fitzpatrick	9ae3bd0939	util/deephash: export a Hash func for use by the control plane name old time/op new time/op delta Hash-6 69.4µs ± 6% 68.4µs ± 4% ~ (p=0.286 n=9+9) HashMapAcyclic-6 115µs ± 5% 115µs ± 4% ~ (p=1.000 n=10+10) name old alloc/op new alloc/op delta Hash-6 2.29kB ± 0% 1.88kB ± 0% -18.13% (p=0.000 n=10+10) HashMapAcyclic-6 2.53kB ± 0% 2.53kB ± 0% ~ (all equal) name old allocs/op new allocs/op delta Hash-6 58.0 ± 0% 54.0 ± 0% -6.90% (p=0.000 n=10+10) HashMapAcyclic-6 202 ± 0% 202 ± 0% ~ (all equal) Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>	3 years ago
Brad Fitzpatrick	700badd8f8	util/deephash: move internal/deephash to util/deephash No code changes. Just a minor package doc addition about lack of API stability.	3 years ago

17 Commits (0e62a7d1a247eb312f340b08e92942f73149f11f)