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Date:      Sat, 30 Jan 2016 21:21:26 +0000 (UTC)
From:      Jilles Tjoelker <jilles@FreeBSD.org>
To:        src-committers@freebsd.org, svn-src-all@freebsd.org, svn-src-head@freebsd.org
Subject:   svn commit: r295085 - head/bin/sh
Message-ID:  <201601302121.u0ULLQRA074931@repo.freebsd.org>
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Author: jilles
Date: Sat Jan 30 21:21:25 2016
New Revision: 295085
URL: https://svnweb.freebsd.org/changeset/base/295085

Log:
  sh: Don't allocate a redirtab if there are no redirections.
  
  Builtins (including variable assignments without command word), function
  calls and redirected compound commands need to restore file descriptors
  to their original state after execution. This is handled by allocating a
  redirtab structure. These mallocs and frees show up heavily in pmcstat.
  
  Only allocate a redirtab if there are actually redirections and maintain a
  count of how many levels of REDIR_PUSH there are without redirtabs.
  
  A simple loop without external programs like
  
  sh -c 'i=0; w=$(printf %0100d 7); while [ "$i" -lt 1000000 ]; do
      i=$((i+1)); done'
  
  is over 25% faster on an amd64 bhyve VM.

Modified:
  head/bin/sh/redir.c

Modified: head/bin/sh/redir.c
==============================================================================
--- head/bin/sh/redir.c	Sat Jan 30 20:48:45 2016	(r295084)
+++ head/bin/sh/redir.c	Sat Jan 30 21:21:25 2016	(r295085)
@@ -70,6 +70,7 @@ struct redirtab {
 	struct redirtab *next;
 	int renamed[10];
 	int fd0_redirected;
+	unsigned int empty_redirs;
 };
 
 
@@ -82,6 +83,9 @@ static struct redirtab *redirlist;
 */
 static int fd0_redirected = 0;
 
+/* Number of redirtabs that have not been allocated. */
+static unsigned int empty_redirs = 0;
+
 static void openredirect(union node *, char[10 ]);
 static int openhere(union node *);
 
@@ -115,12 +119,17 @@ redirect(union node *redir, int flags)
 		memory[i] = 0;
 	memory[1] = flags & REDIR_BACKQ;
 	if (flags & REDIR_PUSH) {
-		sv = ckmalloc(sizeof (struct redirtab));
-		for (i = 0 ; i < 10 ; i++)
-			sv->renamed[i] = EMPTY;
-		sv->fd0_redirected = fd0_redirected;
-		sv->next = redirlist;
-		redirlist = sv;
+		empty_redirs++;
+		if (redir != NULL) {
+			sv = ckmalloc(sizeof (struct redirtab));
+			for (i = 0 ; i < 10 ; i++)
+				sv->renamed[i] = EMPTY;
+			sv->fd0_redirected = fd0_redirected;
+			sv->empty_redirs = empty_redirs - 1;
+			sv->next = redirlist;
+			redirlist = sv;
+			empty_redirs = 0;
+		}
 	}
 	for (n = redir ; n ; n = n->nfile.next) {
 		fd = n->nfile.fd;
@@ -303,6 +312,12 @@ popredir(void)
 	struct redirtab *rp = redirlist;
 	int i;
 
+	INTOFF;
+	if (empty_redirs > 0) {
+		empty_redirs--;
+		INTON;
+		return;
+	}
 	for (i = 0 ; i < 10 ; i++) {
 		if (rp->renamed[i] != EMPTY) {
 			if (rp->renamed[i] >= 0) {
@@ -313,8 +328,8 @@ popredir(void)
 			}
 		}
 	}
-	INTOFF;
 	fd0_redirected = rp->fd0_redirected;
+	empty_redirs = rp->empty_redirs;
 	redirlist = rp->next;
 	ckfree(rp);
 	INTON;

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