top,ps: reduce CPU usage in decimal conversion (optional)

   text    data     bss     dec     hex filename
 734651    3040   14416  752107   b79eb busybox_old
 734751    3040   14416  752207   b7a4f busybox_unstripped

2 files changed, 60 insertions, 2 deletions

diff --git a/libbb/Config.in b/libbb/Config.in
index 5f4e416dd..f82a2b1ce 100644
--- a/libbb/Config.in
+++ b/libbb/Config.in
@@ -26,6 +26,13 @@ config MD5_SIZE_VS_SPEED
           2                   3.0                5088
           3 (smallest)        5.1                4912
 
+config FEATURE_FAST_TOP
+        bool "Faster /proc scanning code (+100 bytes)"
+        default n
+        help
+          This option makes top (and ps) ~20% faster (or 20% less CPU hungry),
+          but code size is slightly bigger.
+
 config FEATURE_ETC_NETWORKS
         bool "Support for /etc/networks"
         default n
diff --git a/libbb/procps.c b/libbb/procps.c
index 1e2495a5a..879cc105a 100644
--- a/libbb/procps.c
+++ b/libbb/procps.c
@@ -107,6 +107,28 @@ void free_procps_scan(procps_status_t* sp)
         free(sp);
 }
 
+#if ENABLE_FEATURE_FAST_TOP
+/* We cut a lot of corners here for speed */
+static unsigned long fast_strtoul_10(char *str, char **endptr)
+{
+        char c;
+        unsigned long n = *str - '0';
+
+        while ((c = *++str) != ' ')
+                n = n*10 + (c - '0');
+
+        *endptr = str + 1; /* We skip trailing space! */
+        return n;
+}
+static char *skip_fields(char *str, int count)
+{
+        do {
+                str = skip_non_whitespace(str); str++;
+        } while (--count);
+        return str;
+}
+#endif
+
 void BUG_comm_size(void);
 procps_status_t* procps_scan(procps_status_t* sp, int flags)
 {
@@ -160,7 +182,9 @@ procps_status_t* procps_scan(procps_status_t* sp, int flags)
 
                 if (flags & PSSCAN_STAT) {
                         char *cp;
+#if !ENABLE_FEATURE_FAST_TOP
                         unsigned long vsz, rss;
+#endif
                         int tty;
 
                         /* see proc(5) for some details on this */
@@ -175,6 +199,8 @@ procps_status_t* procps_scan(procps_status_t* sp, int flags)
                         if (sizeof(sp->comm) < 16)
                                 BUG_comm_size();
                         sscanf(buf, "%*s (%15c", sp->comm);
+
+#if !ENABLE_FEATURE_FAST_TOP
                         n = sscanf(cp+2,
                                 "%c %u "               /* state, ppid */
                                 "%u %u %d %*s "        /* pgid, sid, tty, tpgid */
@@ -197,6 +223,8 @@ procps_status_t* procps_scan(procps_status_t* sp, int flags)
                                 &rss);
                         if (n != 10)
                                 break;
+                        sp->vsz = vsz >> 10; /* vsize is in bytes and we want kb */
+                        sp->rss = rss >> 10;
 
                         sp->tty_str[0] = '?';
                         /* sp->tty_str[1] = '\0'; - done by memset */
@@ -204,6 +232,31 @@ procps_status_t* procps_scan(procps_status_t* sp, int flags)
                                 snprintf(sp->tty_str, sizeof(sp->tty_str), "%u,%u",
                                         (tty >> 8) & 0xfff, /* major */
                                         (tty & 0xff) | ((tty >> 12) & 0xfff00));
+#else
+/* This costs ~100 bytes more but makes top faster by 20%
+ * If you run 10000 processes, this may be important for you */
+                        cp += 2;
+                        sp->state[0] = *cp++; cp++;
+                        sp->ppid = fast_strtoul_10(cp, &cp);
+                        sp->pgid = fast_strtoul_10(cp, &cp);
+                        sp->sid = fast_strtoul_10(cp, &cp);
+                        sp->tty_str[0] = '?';
+                        /* sp->tty_str[1] = '\0'; - done by memset */
+                        tty = fast_strtoul_10(cp, &cp);
+                        if (tty) /* tty field of "0" means "no tty" */
+                                snprintf(sp->tty_str, sizeof(sp->tty_str), "%u,%u",
+                                        (tty >> 8) & 0xfff, /* major */
+                                        (tty & 0xff) | ((tty >> 12) & 0xfff00));
+                        cp = skip_fields(cp, 6); /* tpgid, flags, min_flt, cmin_flt, maj_flt, cmaj_flt */
+                        sp->utime = fast_strtoul_10(cp, &cp);
+                        sp->stime = fast_strtoul_10(cp, &cp);
+                        cp = skip_fields(cp, 3); /* cutime, cstime, priority */
+                        tasknice = fast_strtoul_10(cp, &cp);
+                        cp = skip_fields(cp, 3); /* timeout, it_real_value, start_time */
+                        sp->vsz = fast_strtoul_10(cp, &cp) >> 10; /* vsize is in bytes and we want kb */
+                        sp->rss = fast_strtoul_10(cp, &cp) >> 10;
+#endif
+
                         if (sp->vsz == 0 && sp->state[0] != 'Z')
                                 sp->state[1] = 'W';
                         else
@@ -215,8 +268,6 @@ procps_status_t* procps_scan(procps_status_t* sp, int flags)
                         else
                                 sp->state[2] = ' ';
 
-                        sp->vsz = vsz >> 10; /* vsize is in bytes and we want kb */
-                        sp->rss = rss >> 10;
                 }
 
                 if (flags & PSSCAN_CMD) {