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libfdt: Add FDT_CREATE_FLAG_NO_NAME_DEDUP flag that trades size for speed

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Searching for duplicate names scales O(n^2) with the number of names
added to a fdt, which can cause a noticable slowdown with larger device
trees and very slow CPU cores.

Add FDT_CREATE_FLAG_NO_NAME_DEDUP that allow the caller to trade fdt size
for speed in the creation process.

Signed-off-by: Nicholas Piggin <npiggin@gmail.com>
Message-Id: <20190509094122.834-4-npiggin@gmail.com>
Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
This commit is contained in:
Nicholas Piggin 2019-05-09 19:41:22 +10:00 • committed by David Gibson
parent fbb62754ce
commit ce01b21098
4 changed files with 84 additions and 34 deletions
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39
libfdt/fdt_sw.c
View file

@ -284,6 +284,23 @@ int fdt_end_node(void *fdt)
return 0;
}
static int fdt_add_string_(void *fdt, const char *s)
{
char *strtab = (char *)fdt + fdt_totalsize(fdt);
int strtabsize = fdt_size_dt_strings(fdt);
int len = strlen(s) + 1;
int struct_top, offset;
offset = -strtabsize - len;
struct_top = fdt_off_dt_struct(fdt) + fdt_size_dt_struct(fdt);
if (fdt_totalsize(fdt) + offset < struct_top)
return 0; /* no more room :( */
memcpy(strtab + offset, s, len);
fdt_set_size_dt_strings(fdt, strtabsize + len);
return offset;
}
/* Must only be used to roll back in case of error */
static void fdt_del_last_string_(void *fdt, const char *s)
{
@ -296,10 +313,8 @@ static void fdt_del_last_string_(void *fdt, const char *s)
static int fdt_find_add_string_(void *fdt, const char *s, int *allocated)
{
char *strtab = (char *)fdt + fdt_totalsize(fdt);
const char *p;
int strtabsize = fdt_size_dt_strings(fdt);
int len = strlen(s) + 1;
int struct_top, offset;
const char *p;
*allocated = 0;
@ -307,17 +322,9 @@ static int fdt_find_add_string_(void *fdt, const char *s, int *allocated)
if (p)
return p - strtab;
/* Add it */
*allocated = 1;
offset = -strtabsize - len;
struct_top = fdt_off_dt_struct(fdt) + fdt_size_dt_struct(fdt);
if (fdt_totalsize(fdt) + offset < struct_top)
return 0; /* no more room :( */
memcpy(strtab + offset, s, len);
fdt_set_size_dt_strings(fdt, strtabsize + len);
return offset;
return fdt_add_string_(fdt, s);
}
int fdt_property_placeholder(void *fdt, const char *name, int len, void **valp)
@ -328,7 +335,13 @@ int fdt_property_placeholder(void *fdt, const char *name, int len, void **valp)
FDT_SW_PROBE_STRUCT(fdt);
nameoff = fdt_find_add_string_(fdt, name, &allocated);
/* String de-duplication can be slow, _NO_NAME_DEDUP skips it */
if (sw_flags(fdt) & FDT_CREATE_FLAG_NO_NAME_DEDUP) {
allocated = 1;
nameoff = fdt_add_string_(fdt, name);
} else {
nameoff = fdt_find_add_string_(fdt, name, &allocated);
}
if (nameoff == 0)
return -FDT_ERR_NOSPACE;