disc cache readahead count not being incremented

[Steven M. Schultz]

Subject: disc cache readahead count not being incremented
Index:	sys/ufs_bio.c 2.11BSD

Description:
	If the readahead block is currently in the buffer cache then
	the statistic 'BHITRA' is not incremented.

Repeat-By:
	Install and run the 'trace' program included below.  Observe that 
	the 'bhitra' count remains 0 even though the readahead logic
	is operating correctly.

Fix:
	Apply the patch to ufs_bio.c and remake the kernel.  The 'trace'
	program must be setgid to kmem (the patch to /usr/src/local/Makefile
	will take care of this if a "make install" is done.

#! /bin/sh
# This is a shell archive, meaning:
# 1. Remove everything above the #! /bin/sh line.
# 2. Save the resulting text in a file.
# 3. Execute the file with /bin/sh (not csh) to create:
#	/tmp/c
#	/usr/src/local/trace.c
# This archive created: Sun Jun 30 12:37:45 1991
export PATH; PATH=/bin:/usr/bin:$PATH
if test -f '/tmp/c'
then
	echo shar: "will not over-write existing file '/tmp/c'"
else
sed 's/^X//' << \SHAR_EOF > '/tmp/c'
X*** /sys/sys/ufs_bio.c.old	Mon May 27 02:31:28 1991
X--- /sys/sys/ufs_bio.c	Sat Jun 29 17:04:36 1991
X***************
X*** 81,100 ****
X  	 * If there's a read-ahead block, start i/o
X  	 * on it also (as above).
X  	 */
X! 	if (rablkno && !incore(dev, rablkno)) {
X! 		rabp = getblk(dev, rablkno);
X! 		if (rabp->b_flags & (B_DONE|B_DELWRI)) {
X! 			brelse(rabp);
X! 			trace(TR_BREADHITRA);
X! 		} else {
X! 			rabp->b_flags |= B_READ|B_ASYNC;
X! 			rabp->b_bcount = DEV_BSIZE;	/* XXX? KB */
X! 			(*bdevsw[major(dev)].d_strategy)(rabp);
X! 			trace(TR_BREADMISSRA);
X  #ifdef UCB_RUSAGE
X! 			u.u_ru.ru_inblock++;		/* pay in advance */
X  #endif
X! 		}
X  	}
X  
X  	/*
X--- 81,103 ----
X  	 * If there's a read-ahead block, start i/o
X  	 * on it also (as above).
X  	 */
X! 	if (rablkno) {
X! 		if (!incore(dev, rablkno)) {
X! 			rabp = getblk(dev, rablkno);
X! 			if (rabp->b_flags & (B_DONE|B_DELWRI)) {
X! 				brelse(rabp);
X! 				trace(TR_BREADHITRA);
X! 			} else {
X! 				rabp->b_flags |= B_READ|B_ASYNC;
X! 				rabp->b_bcount = DEV_BSIZE;	/* XXX? KB */
X! 				(*bdevsw[major(dev)].d_strategy)(rabp);
X! 				trace(TR_BREADMISSRA);
X  #ifdef UCB_RUSAGE
X! 				u.u_ru.ru_inblock++;	/* pay in advance */
X  #endif
X! 			}
X! 		} else
X! 			trace(TR_BREADHITRA);	
X  	}
X  
X  	/*
X*** /usr/src/local/Makefile.old	Mon Jul  2 15:18:52 1990
X--- /usr/src/local/Makefile	Sun Jun 30 12:09:42 1991
X***************
X*** 10,16 ****
X  # C programs that live in the current directory and do not need
X  # explicit make lines.
X  #
X! STD= none
X  
X  # C programs that live in the current directory and need explicit make lines.
X  #
X--- 10,16 ----
X  # C programs that live in the current directory and do not need
X  # explicit make lines.
X  #
X! STD= trace
X  
X  # C programs that live in the current directory and need explicit make lines.
X  #
X***************
X*** 32,42 ****
X  
X  # Files listed in ${NSTD} have explicit make lines given below.
X  
X! install:
X  	-for i in ${SUBDIR}; do \
X  		(cd $$i; make ${MFLAGS} DESTDIR=${DESTDIR} install); done
X  	-for i in ${STD} ${NSTD}; do \
X  		(install $$i ${DESTDIR}/usr/local/$$i); done
X  	-for i in ${SHELL}; do \
X  		(install -c -m 755 $$i.sh ${DESTDIR}/usr/local/$$i); done
X  
X--- 32,44 ----
X  
X  # Files listed in ${NSTD} have explicit make lines given below.
X  
X! install: ${SUBDIR} ${STD} ${NSTD}
X  	-for i in ${SUBDIR}; do \
X  		(cd $$i; make ${MFLAGS} DESTDIR=${DESTDIR} install); done
X  	-for i in ${STD} ${NSTD}; do \
X  		(install $$i ${DESTDIR}/usr/local/$$i); done
X+ 	-chmod 2755 ${DESTDIR}/usr/local/trace
X+ 	-chgrp kmem ${DESTDIR}/usr/local/trace
X  	-for i in ${SHELL}; do \
X  		(install -c -m 755 $$i.sh ${DESTDIR}/usr/local/$$i); done
X  
SHAR_EOF
fi
if test -f '/usr/src/local/trace.c'
then
	echo shar: "will not over-write existing file '/usr/src/local/trace.c'"
else
sed 's/^X//' << \SHAR_EOF > '/usr/src/local/trace.c'
X#include <stdio.h>
X#include <nlist.h>
X#include <signal.h>
X#include <sys/trace.h>
X
Xstruct	nlist nl[] =
X	{
X	{ "_tracebuf" },
X	{ "" },
X	};
X
X	int	mf, hdr(), lines = 1;
X
Xmain(argc, argv)
X	int argc;
X	char **argv;
X	{
X	register i;
X	int	iter;
X
X	nlist("/vmunix", nl);
X	if	(nl[0].n_type == 0)
X		{
X		fprintf(stderr, "no /vmunix namelist\n");
X		exit(1);
X	}
X	mf = open("/dev/kmem", 0);
X	if	(mf < 0)
X		{
X		fprintf(stderr, "cannot open /dev/kmem\n");
X		exit(1);
X		}
X	iter = 0;
X	argc--, argv++;
X	if	(argc > 1)
X		iter = atoi(argv[1]);
X	signal(SIGCONT, hdr);
Xloop:
X	if	(--lines == 0)
X		hdr();
X	nmstats();
X	fflush(stdout);
X	if	(--iter &&argc > 0)
X		{
X		sleep(atoi(argv[0]));
X		goto loop;
X		}
X	}
X
Xhdr()
X	{
X
X	puts("bhit      bmiss     bwrite    bhitra    bmissra   brelse    %bhit");
X	lines = 19;
X	}
X
Xnmstats()
X	{
X	float	pct;
X	long	tracebuf[TR_NUM_210];
X
X	lseek(mf, (long)nl[0].n_value, 0);
X	read(mf, tracebuf, sizeof tracebuf);
X	pct = tracebuf[TR_BREADHIT];
X	pct /= (tracebuf[TR_BREADHIT] + tracebuf[TR_BREADMISS]);
X	pct *= 100.0;
X	printf("%-9D %-9D %-9D %-9D %-9D %-9D %.2f\n",
X		tracebuf[TR_BREADHIT],
X		tracebuf[TR_BREADMISS],
X		tracebuf[TR_BWRITE],
X		tracebuf[TR_BREADHITRA],
X		tracebuf[TR_BREADMISSRA],
X		tracebuf[TR_BRELSE],
X		pct);
X	}
SHAR_EOF
fi
exit 0
#	End of shell archive