Where syslogd would have fsync()ed a file in the past, instead set a flag

FFLAG_NEEDSYNC and fsync the file when select() next returns zero.  This
dramatically speeds up the process of logging large amounts of data, while
leaving the essential semantics (that data can be expected to be on disk
if we crash) unchanged.

In my tests, this speeds up the rc phase of booting by 18-20%. [1]

YES PLEASE! by:	phk [1]

1 files changed, 25 insertions, 3 deletions

diff --git a/usr.sbin/syslogd/syslogd.c b/usr.sbin/syslogd/syslogd.c
index 367901c..5721437 100644
--- a/usr.sbin/syslogd/syslogd.c
+++ b/usr.sbin/syslogd/syslogd.c
@@ -188,6 +188,7 @@ struct filed {
 	u_int	f_repeatcount;			/* number of "repeated" msgs */
 	int	f_flags;			/* file-specific flags */
 #define FFLAG_SYNC 0x01
+#define FFLAG_NEEDSYNC	0x02
 };
 
 /*
@@ -292,6 +293,7 @@ static int	UniquePriority;	/* Only log specified priority? */
 static int	LogFacPri;	/* Put facility and priority in log message: */
 				/* 0=no, 1=numeric, 2=names */
 static int	KeepKernFac;	/* Keep remotely logged kernel facility */
+static int	needdofsync = 0; /* Are any file(s) waiting to be fsynced? */
 
 volatile sig_atomic_t MarkSet, WantDie;
 
@@ -304,6 +306,7 @@ static int	deadq_remove(pid_t);
 static int	decode(const char *, CODE *);
 static void	die(int);
 static void	dodie(int);
+static void	dofsync();
 static void	domark(int);
 static void	fprintlog(struct filed *, int, const char *);
 static int	*socksetup(int, const char *);
@@ -557,9 +560,12 @@ main(int argc, char *argv[])
 				FD_SET(funix[i], fdsr);
 		}
 
-		i = select(fdsrmax+1, fdsr, NULL, NULL, tvp);
+		i = select(fdsrmax+1, fdsr, NULL, NULL,
+		    needdofsync ? &tv : tvp);
 		switch (i) {
 		case 0:
+			dofsync();
+			needdofsync = 0;
 			if (tvp) {
 				tvp = NULL;
 				if (ppid != 1)
@@ -976,6 +982,20 @@ logmsg(int pri, const char *msg, const char *from, int flags)
 }
 
 static void
+dofsync(void)
+{
+	struct filed *f;
+
+	for (f = Files; f; f = f->f_next) {
+		if ((f->f_type == F_FILE) &&
+		    (f->f_flags & FFLAG_NEEDSYNC)) {
+			f->f_flags &= ~FFLAG_NEEDSYNC;
+			(void)fsync(f->f_file);
+		}
+	}
+}
+
+static void
 fprintlog(struct filed *f, int flags, const char *msg)
 {
 	struct iovec iov[7];
@@ -1153,8 +1173,10 @@ fprintlog(struct filed *f, int flags, const char *msg)
 			f->f_type = F_UNUSED;
 			errno = e;
 			logerror(f->f_un.f_fname);
-		} else if ((flags & SYNC_FILE) && (f->f_flags & FFLAG_SYNC))
-			(void)fsync(f->f_file);
+		} else if ((flags & SYNC_FILE) && (f->f_flags & FFLAG_SYNC)) {
+			f->f_flags |= FFLAG_NEEDSYNC;
+			needdofsync = 1;
+		}
 		break;
 
 	case F_PIPE: