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Nest: FIB rehash values tweaked for better performance

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This commit is contained in:
Maria Matejka 2019-01-29 15:19:06 +01:00
parent e85e37d91d
commit a8d0f2516c
1 changed files with 44 additions and 3 deletions
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45
nest/rt-fib.c
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@ -58,9 +58,50 @@
#include "nest/route.h"
#include "lib/string.h"
/*
* The FIB rehash values are maintaining FIB count between N/5 and 2N. What
* does it mean?
*
* +------------+--------+---------+-----------+----------+-----------+
* | Table size | Memory | Min cnt | net + rte | Max cnt | net + rte |
* +------------+--------+---------+-----------+----------+-----------+
* | 1k | 8k | 0 | 0 | 2k | 192 k |
* | 2k | 16k | 409 | 38.3k | 4k | 384 k |
* | 4k | 32k | 819 | 76.8k | 8k | 768 k |
* | 8k | 64k | 1.6k | 153.6k | 16k | 1.5M |
* | 16k | 128k | 3.2k | 307.1k | 32k | 3 M |
* | 32k | 256k | 6.4k | 614.3k | 64k | 6 M |
* | 64k | 512k | 12.8k | 1.2M | 128k | 12 M |
* | 128k | 1024k | 25.6k | 2.4M | 256k | 24 M |
* | 256k | 2M | 51.2k | 4.8M | 512k | 48 M |
* | 512k | 4M | 102.4k | 9.6M | 1M | 96 M |
* | 1M | 8M | 204.8k | 19.2M | 2M | 192 M |
* | 2M | 16M | 409.6k | 38.4M | 4M | 384 M |
* | 4M | 32M | 819.2k | 76.8M | 8M | 768 M |
* | 8M | 64M | 1.6M | 153.6M | infinity | infinity |
* +------------+--------+---------+-----------+----------+-----------+
*
* Table size shows how many slots are in FIB table.
* Memory shows how much memory is eaten by FIB table.
* Min cnt minimal number of nets in table of given size
* Max cnt maximal number of nets in table of given size
* net + rte memory eaten by 1 net and one route in it for min cnt and max cnt
*
* Example: If we have 750,000 network entries in a table:
* * the table size may be 512k if we have never had more
* * the table size may be 1M or 2M if we at least happened to have more
* * 256k is too small, 8M is too big
*
* When growing, rehash is done on demand so we do it on every power of 2.
* When shrinking, rehash is done on delete which is done (in global tables)
* in a scheduled event. Rehashing down 2 steps.
*
*/
#define HASH_DEF_ORDER 10
#define HASH_HI_MARK *4
#define HASH_HI_STEP 2
#define HASH_HI_MARK * 2
#define HASH_HI_STEP 1
#define HASH_HI_MAX 24
#define HASH_LO_MARK / 5
#define HASH_LO_STEP 2