linux/scripts/kconfig/expr.h, branch v2.6.35

Improve kconfig symbol hashing

2010-02-02T13:33:55Z

While looking for something else I noticed that the symbol hash function used by kconfig is quite poor. It doesn't use any of the standard hash techniques but simply adds up the string and then uses power of two masking, which is both known to perform poorly. The current x86 kconfig has over 7000 symbols. When I instrumented it showed that the minimum hash chain length was 16 and a significant number of them was over 30. It didn't help that the hash table size was only 256 buckets. This patch increases the hash table size to a larger prime and switches to a FNV32 hash. I played around with a couple of hash functions, but that one seemed to perform best with reasonable hash table sizes. Increasing the hash table size even further didn't seem like a good idea, because there are a couple of global walks which walk the complete hash table. I also moved the unnamed bucket to 0. It's still the longest of all the buckets (44 entries), but hopefully it's not often hit except for the global walk which doesn't care. The result is a much nicer distribution: (first column bucket length, second number of buckets with that length) 1: 3505 2: 1236 3: 294 4: 52 5: 3 47: 1 <--- this is the unnamed symbols bucket There are still some 5+ buckets, but increasing the hash table even more would be likely not worth it. This also cleans up the code slightly by removing hard coded magic numbers. I didn't notice a big performance difference either way on my Nehalem system, but I presume it'll help somewhat on slower systems. Signed-off-by: Andi Kleen Signed-off-by: Michal Marek

kconfig: struct property commented

2009-01-02T19:43:21Z

No functional changes Signed-off-by: Sam Ravnborg

kconfig: add comments to symbol flags

2009-01-02T19:43:21Z

No functional changes - only comments. Signed-off-by: Sam Ravnborg

kconfig: explain symbol value defaults

2009-01-02T19:43:20Z

Added a few comments - no functional change. Signed-off-by: Sam Ravnborg

kconfig: environment symbol support

2008-01-28T22:14:39Z

Add the possibility to import a value from the environment into kconfig via the option syntax. Beside flexibility this has the advantage providing proper dependencies. Documented the options syntax. Signed-off-by: Roman Zippel Signed-off-by: Sam Ravnborg

kconfig: explicitly introduce expression list

2008-01-28T22:14:39Z

Rename E_CHOICE to E_LIST to explicitly add support for expression lists. Add a helper macro expr_list_for_each_sym to more easily iterate over the list. Signed-off-by: Roman Zippel Signed-off-by: Sam Ravnborg

kconfig: delete unused FILE_ and SYMBOL_ flags

2008-01-28T22:14:38Z

The *_PRINTED flags were never used - so delete them. Do we need them later then we can re-add them. Signed-off-by: Sam Ravnborg Cc: Roman Zippel

kconfig: rename E_OR & friends to avoid name clash

2008-01-28T22:14:38Z

We had macros named the same as a set of enumeration values. It is legal code but very confusing to read - so rename the macros from E_* to EXPR_* Signed-off-by: Sam Ravnborg Cc: Roman Zippel

kconfig: remove unused members from struct symbol

2007-07-25T19:14:30Z

dep and dep2 in struct symbol was unused - remove them. Signed-off-by: Sam Ravnborg Cc: Roman Zippel

kconfig: attach help text to menus

2007-07-25T19:14:26Z

Roman Zippel wrote: > A simple example would be > help texts, right now they are per symbol, but they should really be per > menu, so archs can provide different help texts for something. This patch does this and at the same time introduce a few API funtions used to access the help text. The relevant api functions are introduced in the various frontends. Signed-off-by: Sam Ravnborg Cc: Roman Zippel