Sometimes code is much simpler if we can statically initialize data
structures. Until now, this has not been possible for cmap-based data
structures, so this commit introduces a CMAP_INITIALIZER macro.
This works by adding a singleton empty cmap_impl that simply forces the
first insertion into any cmap that points to it to allocate a real
cmap_impl. There could be some risk that rogue code modifies the
singleton, so for safety it is also marked 'const' to allow the linker to
put it into a read-only page.
This adds a new OVS_ALIGNED_VAR macro with GCC and MSVC implementations.
The latter is based on Microsoft webpages, so developers who know Windows
might want to scrutinize it.
As examples of the kind of simplification this can make possible, this
commit removes an initialization function from ofproto-dpif-rid.c and a
call to cmap_init() from tnl-neigh-cache.c. An upcoming commit will add
another user.
CC: Jarno Rajahalme <jarno@ovn.org>
CC: Gurucharan Shetty <guru@ovn.org>
Signed-off-by: Ben Pfaff <blp@ovn.org>
Acked-by: Ryan Moats <rmoats@us.ibm.com>
Commit d916785ce98c("dpif-netdev: Fix improper use of CMAP_FOR_EACH.")
fixes a problem that's worth documenting.
Requested-by: Jarno Rajahalme <jarno@ovn.org>
Signed-off-by: Daniele Di Proietto <diproiettod@vmware.com>
Acked-by: Ben Pfaff <blp@ovn.org>
Batching the cmap find improves the memory behavior with large cmaps
and can make searches twice as fast:
$ tests/ovstest test-cmap benchmark 2000000 8 0.1 16
Benchmarking with n=2000000, 8 threads, 0.10% mutations, batch size 16:
cmap insert: 533 ms
cmap iterate: 57 ms
batch search: 146 ms
cmap destroy: 233 ms
cmap insert: 552 ms
cmap iterate: 56 ms
cmap search: 299 ms
cmap destroy: 229 ms
hmap insert: 222 ms
hmap iterate: 198 ms
hmap search: 2061 ms
hmap destroy: 209 ms
Batch size 1 has small performance penalty, but all other batch sizes
are faster than non-batched cmap_find(). The batch size 16 was
experimentally found better than 8 or 32, so now
classifier_lookup_miniflow_batch() performs the cmap find operations
in batches of 16.
Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
This makes the following patch easier and cleans up the code.
Explicit "inline" keywords seem necessary to prevent performance
regression on cmap_find() with GCC 4.7 -O2.
Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
We already update the count field as the last step of these functions,
so returning the current count is very cheap. Callers that care about
the count become a bit more efficient, as they avoid extra
non-inlineable function call.
Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
Implementation of OBJECT_OFFSETOF() for non-GNUC compilers like MSVC
causes "uninitialized variable" warnings. Since OBJECT_OFFSETOF() is
indirectly used through all the *_FOR_EACH() (through ASSIGN_CONTAINER()
and OBJECT_CONTAINING()) macros, the OVS build
on Windows gets littered with "uninitialized variable" warnings.
This patch attempts to workaround the problem.
Signed-off-by: Gurucharan Shetty <gshetty@nicira.com>
Acked-by: Alin Gabriel Serdean <aserdean@cloudbasesolutions.com>
Acked-by: Saurabh Shah <ssaurabh@vmware.com>
Acked-by: Ben Pfaff <blp@nicira.com>
There isn't any significant downside to making cmap iteration "safe" all
the time, so this drops the _SAFE variant.
Similar changes to CMAP_CURSOR_FOR_EACH and CMAP_CURSOR_FOR_EACH_CONTINUE.
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
CMAP_FOR_EACH and CLS_FOR_EACH and their variants tried to use void ** as
a "pointer to any kind of pointer". That is a violation of the aliasing
rules in ISO C which technically yields undefined behavior. With GCC 4.1,
it causes both warnings and actual misbehavior. One option would to add
-fno-strict-aliasing to the compiler flags, but that would only help with
GCC; who knows whether this can be worked around with other compilers.
Instead, this commit rewrites the iterators to avoid disallowed pointer
aliasing.
VMware-BZ: #1287651
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
This further eases porting existing hmap code to use cmap instead.
The iterator variants taking an explicit cursor are retained (renamed)
as they are needed when iteration is to be continued from the last
iterated node.
Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Add cmap_replace() and cmap_first(), as well as CMAP_FOR_EACH_SAFE and
CMAP_FOR_EACH_CONTINUE to make porting existing hmap using code a bit
easier.
CMAP_FOR_EACH_SAFE is useful in RCU postponed destructors, when it is
known that additional postponing is not needed.
Signed-off-by: Jarno Rajahalme <jrajahalme@nicira.com>
Acked-by: Ben Pfaff <blp@nicira.com>
This implements an "optimistic concurrent cuckoo hash", a single-writer,
multiple-reader hash table data structure. The point of this data
structure is performance, so this commit message focuses on performance.
I tested the performance of cmap with the test-cmap utility included in
this commit. It takes three parameters for benchmarking:
- n, the number of elements to insert.
- n_threads, the number of threads to use for searching and
mutating the hash table.
- mutations, the percentage of operations that should modify the
hash table, from 0% to 100%.
e.g. "test-cmap 1000000 16 1" inserts one million elements, uses 16
threads, and 1% of the operations modify the hash table.
Any given run does the following for both hmap and cmap
implementations:
- Inserts n elements into a hash table.
- Iterates over all of the elements.
- Spawns n_threads threads, each of which searches for each of the
elements in the hash table, once, and removes the specified
percentage of them.
- Removes each of the (remaining) elements and destroys the hash
table.
and reports the time taken by each step,
The tables below report results for various parameters with a draft version
of this library. The tests were not formally rerun for the final version,
but the intermediate changes should only have improved performance, and
this seemed to be the case in some informal testing.
n_threads=16 was used each time, on a 16-core x86-64 machine. The compiler
used was Clang 3.5. (GCC yields different numbers but similar relative
results.)
The results show:
- Insertion is generally 3x to 5x faster in an hmap.
- Iteration is generally about 3x faster in a cmap.
- Search and mutation is 4x faster with .1% mutations and the
advantage grows as the fraction of mutations grows. This is
because a cmap does not require locking for read operations,
even in the presence of a writer.
With no mutations, however, no locking is required in the hmap
case, and the hmap is somewhat faster. This is because raw hmap
search is somewhat simpler and faster than raw cmap search.
- Destruction is faster, usually by less than 2x, in an hmap.
n=10,000,000:
.1% mutations 1% mutations 10% mutations no mutations
cmap hmap cmap hmap cmap hmap cmap hmap
insert: 6132 2182 6136 2178 6111 2174 6124 2180
iterate: 370 1203 378 1201 370 1200 371 1202
search: 1375 8692 2393 28197 18402 80379 1281 1097
destroy: 1382 1187 1197 1034 324 241 1405 1205
n=1,000,000:
.1% mutations 1% mutations 10% mutations no mutations
cmap hmap cmap hmap cmap hmap cmap hmap
insert: 311 25 310 60 311 59 310 60
iterate: 25 62 25 64 25 57 25 60
search: 115 637 197 2266 1803 7284 101 67
destroy: 103 64 90 59 25 13 104 66
n=100,000:
.1% mutations 1% mutations 10% mutations no mutations
cmap hmap cmap hmap cmap hmap cmap hmap
insert: 25 6 26 5 25 5 25 5
iterate: 1 3 1 3 1 3 2 3
search: 12 57 27 219 164 735 10 5
destroy: 5 3 6 3 2 1 6 4
Signed-off-by: Ben Pfaff <blp@nicira.com>
Acked-by: Jarno Rajahalme <jrajahalme@nicira.com>
