Add some qp-trie tracing macros which can be enabled by a
developer. These print a message when a leaf is attached or
detached, indicating which part of the qp-trie implementation
did so. The refcount methods must now return the refcount value
so it can be printed by the trace macros.
The first working multi-threaded qp-trie was stuck with an unpleasant
trade-off:
* Use `isc_rwlock`, which has acceptable write performance, but
terrible read scalability because the qp-trie made all accesses
through a single lock.
* Use `liburcu`, which has great read scalability, but terrible
write performance, because I was relying on `rcu_synchronize()`
which is rather slow. And `liburcu` is LGPL.
To get the best of both worlds, we need our own scalable read side,
which we now have with `isc_qsbr`. And we need to modify the write
side so that it is not blocked by readers.
Better write performance requires an async cleanup function like
`call_rcu()`, instead of the blocking `rcu_synchronize()`. (There
is no blocking cleanup in `isc_qsbr`, because I have concluded
that it would be an attractive nuisance.)
Until now, all my multithreading qp-trie designs have been based
around two versions, read-only and mutable. This is too few to
work with asynchronous cleanup. The bare minimum (as in epoch
based reclamation) is three, but it makes more sense to support an
arbitrary number. Doing multi-version support "properly" makes
fewer assumptions about how safe memory reclamation works, and it
makes snapshots and rollbacks simpler.
To avoid making the memory management even more complicated, I
have introduced a new kind of "packed reader node" to anchor the
root of a version of the trie. This is simpler because it re-uses
the existing chunk lifetime logic - see the discussion under
"packed reader nodes" in `qp_p.h`.
I have also made the chunk lifetime logic simpler. The idea of a
"generation" is gone; instead, chunks are either mutable or
immutable. And the QSBR phase number is used to indicate when a
chunk can be reclaimed.
Instead of the `shared_base` flag (which was basically a one-bit
reference count, with a two version limit) the base array now has a
refcount, which replaces the confusing ad-hoc lifetime logic with
something more familiar and systematic.
Adjust the dns_qp_memusage() and dns_qp_compact() functions
to be more informative and flexible about handling fragmentation.
Avoid wasting space in runt chunks.
Switch from twigs_mutable() to cells_immutable() because that is the
sense we usually want.
Drop the redundant evacuate() function and rename evacuate_twigs() to
evacuate(). Move some chunk test functions closer to their point of
use.
Clarify compact_recursive(). Some small cleanups to comments.
Use isc_time_monotonic() for qp-trie timing stats.
Use #define constants to control debug logging.
Set up DNS name label offsets in dns_qpkey_fromname() so it is easier
to use in cases where the name is not fully hydrated.
The main benchmark is `qpmulti`, which exercizes the qp-trie
transactional API with differing numbers of threads and differing data
sizes, to get some idea of how its performance scales.
The `load-names` benchmark compares the times to populate and query
and the memory used by various BIND data structures: qp-trie, hash
table (chained), hash map (closed), and red-black tree.
The `qp-dump` program is a test utility rather than a benchmark. It
populates a qp-trie and prints it out, either in an ad-hoc text
format, or as input to the graphviz `dot` program.
Since this is very sensitive code which has often had security
problems in many DNS implementations, it needs a decent amount of
validation. This fuzzer ensures that the new code has the same output
as the old code, and that it doesn't take longer than a second.
The benchmark uses the fuzzer's copy of the old dns_name_fromwire()
code to compare a number of scenarios: many compression pointers, many
labels, long labels, random data, with/without downcasing.
Instead of fixing a Coverity complaint (and other style nits),
delete it because it needs input data that can't be generated
with the tools that ship with BIND.
The `render` benchmark loads some binary DNS message dumps and
repeatedly passes them to `dns_message_render`.
The `compress` benchmark loads a list of domain names and packs them
into 4KiB chunks using `dns_name_towire`.
Coverity is optimistic that we might do thousands of hashes in less
than a microsecond.
/tests/bench/siphash.c: 54 in main()
48 count++;
49 }
50
51 isc_time_now_hires(&finish);
52
53 us = isc_time_microdiff(&finish, &start);
>>> CID 358309: Integer handling issues (DIVIDE_BY_ZERO)
>>> In expression "count * 1000UL / us", division by expression "us" which may be zero has undefined behavior.
54 printf("%f us wide-lower len %3zu, %7llu kh/s (%llx)\n",
55 (double)us / 1000000.0, len,
56 (unsigned long long)(count * 1000 / us),
57 (unsigned long long)sum);
58 }
59
Formerly, the isc_hash32() would have to change the key in a local copy
to make it case insensitive. Change the isc_siphash24() and
isc_halfsiphash24() functions to lowercase the input directly when
reading it from the memory and converting the uint8_t * array to
64-bit (respectively 32-bit numbers).
