kmod/libkmod
Lucas De Marchi 82fc7d986c libkmod-hash: always align n_buckets to power of 2
By aligning n_buckets to power of 2 we can turn the "bucket = hashval %
n_buckets" into a less expensive bucket = hashval & (n_buckets - 1).
This removes the DIV instruction as shown below.

Before:
	xor    %edx,%edx
	divl   0x8(%rbx)
	mov    %edx,%eax
	add    $0x1,%rax
	shl    $0x4,%rax
	add    %rbx,%rax

After:
	lea    -0x1(%rdi),%edx
	and    %edx,%eax
	add    $0x1,%rax
	shl    $0x4,%rax
	add    %rbx,%rax

With a microbenchmark, measuring the time to locate the bucket (i.e.
time_to_calculate_hashval + time_to_calculate_bucket_position) we have
the results below (time in clock cycles):

	keylen      before   after
	2-10          79.0    61.9 (-21.65%)
	11-17         81.0    64.4 (-20.48%)
	18-25         90.0    73.2 (-18.69%)
	26-32        104.7    87.0 (-16.82%)
	33-40        108.4    89.6 (-17.37%)
	41-48        111.2    91.9 (-17.38%)
	49-55        120.1   102.1 (-15.04%)
	56-63        134.4   115.7 (-13.91%)

As expected the gain is constant, regardless of the key length.
The time to clculate the hashval varies with the key length, which
explains the bigger gains for short keys.
2013-09-20 01:10:37 -05:00
..
docs Use "-internal" suffix instead of "-private" 2013-07-04 16:13:11 -03:00
.gitignore Rename libabc to libkmod 2011-11-21 14:35:35 -02:00
COPYING Change licenses 2011-12-12 18:24:35 -02:00
libkmod-array.c Update copyright notices 2013-01-16 11:27:45 -02:00
libkmod-array.h Use #pragma once instead of #ifndef 2012-07-18 10:31:50 -03:00
libkmod-config.c Fix usage of readdir_r() 2013-08-29 01:33:51 -03:00
libkmod-elf.c Use "-internal" suffix instead of "-private" 2013-07-04 16:13:11 -03:00
libkmod-file.c Use "-internal" suffix instead of "-private" 2013-07-04 16:13:11 -03:00
libkmod-hash.c libkmod-hash: always align n_buckets to power of 2 2013-09-20 01:10:37 -05:00
libkmod-hash.h Use #pragma once instead of #ifndef 2012-07-18 10:31:50 -03:00
libkmod-index.c Use "-internal" suffix instead of "-private" 2013-07-04 16:13:11 -03:00
libkmod-index.h Update copyright notices 2013-01-16 11:27:45 -02:00
libkmod-internal.h Use "-internal" suffix instead of "-private" 2013-07-04 16:13:11 -03:00
libkmod-list.c Use "-internal" suffix instead of "-private" 2013-07-04 16:13:11 -03:00
libkmod-module.c Fix usage of readdir_r() 2013-08-29 01:33:51 -03:00
libkmod-signature.c Use "-internal" suffix instead of "-private" 2013-07-04 16:13:11 -03:00
libkmod-util.c util: Add mkdir_parents() 2013-07-15 12:45:35 -03:00
libkmod-util.h util: Add ALIGN_POWER2 2013-09-20 01:08:46 -05:00
libkmod.c Use "-internal" suffix instead of "-private" 2013-07-04 16:13:11 -03:00
libkmod.h Update copyright notices 2013-01-16 11:27:45 -02:00
libkmod.pc.in libkmod: remove external cflags from .pc file 2011-12-24 20:28:11 +01:00
libkmod.sym build: remove private symbol from linker script 2012-05-10 21:11:27 -03:00
macro.h build: remove check for typeof 2013-09-06 11:31:35 -03:00
missing.h libkmod: Avoid calling syscall() with -1 2013-05-11 00:54:15 -03:00
README README: Move items from TODO 2013-07-17 02:31:27 -03:00

libkmod - linux kernel module handling library

ABSTRACT
========

libkmod was created to allow programs to easily insert, remove and
list modules, also checking its properties, dependencies and aliases.

there is no shared/global context information and it can be used by
multiple sites on a single program, also being able to be used from
threads, although it's not thread safe (you must lock explicitly).


OVERVIEW
========

Every user should create and manage it's own library context with:

   struct kmod_ctx *ctx = kmod_new(kernel_dirname);
   kmod_unref(ctx);


Modules can be created by various means:

   struct kmod_module *mod;
   int err;

   err = kmod_module_new_from_path(ctx, path, &mod);
   if (err < 0) {
      /* code */
   } else {
      /* code */
      kmod_module_unref(mod);
   }

   err = kmod_module_new_from_name(ctx, name, &mod);
   if (err < 0) {
      /* code */
   } else {
      /* code */
      kmod_module_unref(mod);
   }


Or could be resolved from a known alias to a list of alternatives:

   struct kmod_list *list, *itr;
   int err;
   err = kmod_module_new_from_lookup(ctx, alias, &list);
   if (err < 0) {
      /* code */
   } else {
      kmod_list_foreach(itr, list) {
         struct kmod_module *mod = kmod_module_get_module(itr);
         /* code */
      }
   }