Dne 23.8.2016 v 20:47 Alexey Dobriyan napsal(a):
> Do you think kernel build is 100% dominated by gcc? You are wrong!
> One small utility called "fixdep" consistently manages to sneak into
> profile's first page (unless you have small monitor of course).
>
> The choke point is this clever code:
>
> for (; m < end; m++) {
> if (*m == INT_CONF) { p = (char *) m ; goto conf; }
> if (*m == INT_ONFI) { p = (char *) m-1; goto conf; }
> if (*m == INT_NFIG) { p = (char *) m-2; goto conf; }
> if (*m == INT_FIG_) { p = (char *) m-3; goto conf; }
>
> 4 branches per 4 characters is not fast.
>
> Use strstr(3), so that SSE2 etc can be used.
It should be noted that the previous code also matched nested CONFIG_*
strings, like CONFIG_PROC inside CONFIG_IKCONFIG_PROC. But these are
pointless, so your patch is removing a few false matches.
> With this patch, fixdep is so deep at the bottom, it is hard to find it.
Nice.
> - if (*m == INT_CONF) { p = (char *) m ; goto conf; }
> - if (*m == INT_ONFI) { p = (char *) m-1; goto conf; }
> - if (*m == INT_NFIG) { p = (char *) m-2; goto conf; }
> - if (*m == INT_FIG_) { p = (char *) m-3; goto conf; }
Please also remove the INT_* definitions and the test at startup.
> + map = malloc(st.st_size + 1);
> + if (!map) {
> + perror("fixdep: malloc");
> close(fd);
> return;
> }
> + if (read(fd, map, st.st_size) != st.st_size) {
> + perror("fixdep: read");
> + close(fd);
> + return;
> + }
I wanted to suggest memmem() instead of strstr() to avoid the extra
copy, but that would make use depend on glibc (this _might_ have been
the reason to use the manual string search, in fact). So let's leave
this as.
Michal
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