Date: Sat, 18 Dec 1999 20:16:53 -0800 (PST) From: Matthew Dillon <dillon@apollo.backplane.com> To: Greg Lehey <grog@lemis.com> Cc: FreeBSD current users <FreeBSD-current@FreeBSD.ORG> Subject: Re: Recent current hangs frequently for 1 to 2 seconds. Message-ID: <199912190416.UAA01125@apollo.backplane.com> References: <19991219143759.C465@freebie.lemis.com>
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:I've just upgraded to -CURRENT as of yesterday, and I'm noticing a
:number of occasions where all activity ceases for a second or two at a
:time; it seems to be related to IDE disk activity with the new ATA
:driver, but I don't have much evidence. I'm running a SiS 5591
:chipset. Has anybody else seen something like this?
:
:Greg
It's possible that the blockages you are seeing are due to the ATA
driver, but it's also possible that they are due to a bug in the
buffer cache flushing code which the following patch fixes. So try
the patch and see if that fixes your problem. If it doesn't then
we can at least rule it out as being the cause of the problem you
are seeing.
(This patch is currently slated for commit on Sunday).
-Matt
Matthew Dillon
<dillon@backplane.com>
Index: vfs_bio.c
===================================================================
RCS file: /home/ncvs/src/sys/kern/vfs_bio.c,v
retrieving revision 1.237
diff -u -r1.237 vfs_bio.c
--- vfs_bio.c 1999/12/01 02:09:29 1.237
+++ vfs_bio.c 1999/12/17 18:44:40
@@ -88,7 +88,7 @@
bufmallocspace, maxbufmallocspace, hibufspace;
static int maxbdrun;
static int needsbuffer;
-static int numdirtybuffers, lodirtybuffers, hidirtybuffers;
+static int numdirtybuffers, hidirtybuffers;
static int numfreebuffers, lofreebuffers, hifreebuffers;
static int getnewbufcalls;
static int getnewbufrestarts;
@@ -96,8 +96,6 @@
SYSCTL_INT(_vfs, OID_AUTO, numdirtybuffers, CTLFLAG_RD,
&numdirtybuffers, 0, "");
-SYSCTL_INT(_vfs, OID_AUTO, lodirtybuffers, CTLFLAG_RW,
- &lodirtybuffers, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, hidirtybuffers, CTLFLAG_RW,
&hidirtybuffers, 0, "");
SYSCTL_INT(_vfs, OID_AUTO, numfreebuffers, CTLFLAG_RD,
@@ -275,6 +273,16 @@
}
}
+/*
+ * bd_speedup - speedup the buffer cache flushing code
+ */
+
+static __inline__
+void
+bd_speedup(void)
+{
+ bd_wakeup(1);
+}
/*
* Initialize buffer headers and related structures.
@@ -353,7 +361,6 @@
* Reduce the chance of a deadlock occuring by limiting the number
* of delayed-write dirty buffers we allow to stack up.
*/
- lodirtybuffers = nbuf / 7 + 10;
hidirtybuffers = nbuf / 4 + 20;
numdirtybuffers = 0;
/*
@@ -365,14 +372,9 @@
* the buffer cache.
*/
while (hidirtybuffers * BKVASIZE > 3 * hibufspace / 4) {
- lodirtybuffers >>= 1;
hidirtybuffers >>= 1;
buf_maxio >>= 1;
}
- if (lodirtybuffers < 2) {
- lodirtybuffers = 2;
- hidirtybuffers = 4;
- }
/*
* Temporary, BKVASIZE may be manipulated soon, make sure we don't
@@ -799,9 +801,9 @@
void
bwillwrite(void)
{
- int twenty = (hidirtybuffers - lodirtybuffers) / 5;
+ int slop = hidirtybuffers / 10;
- if (numdirtybuffers > hidirtybuffers + twenty) {
+ if (numdirtybuffers > hidirtybuffers + slop) {
int s;
s = splbio();
@@ -1571,9 +1573,8 @@
flags = VFS_BIO_NEED_ANY;
}
- /* XXX */
+ bd_speedup(); /* heeeelp */
- (void) speedup_syncer();
needsbuffer |= flags;
while (needsbuffer & flags) {
if (tsleep(&needsbuffer, (PRIBIO + 4) | slpflag,
@@ -1652,6 +1653,7 @@
static struct proc *bufdaemonproc;
static int bd_interval;
static int bd_flushto;
+static int bd_flushinc;
static struct kproc_desc buf_kp = {
"bufdaemon",
@@ -1672,6 +1674,7 @@
bd_interval = 5 * hz; /* dynamically adjusted */
bd_flushto = hidirtybuffers; /* dynamically adjusted */
+ bd_flushinc = 1;
while (TRUE) {
bd_request = 0;
@@ -1694,44 +1697,38 @@
}
}
- /*
- * If nobody is requesting anything we sleep
- */
- if (bd_request == 0)
- tsleep(&bd_request, PVM, "psleep", bd_interval);
+ if (bd_request ||
+ tsleep(&bd_request, PVM, "psleep", bd_interval) == 0) {
+ /*
+ * Another request is pending or we were woken up
+ * without timing out. Flush more.
+ */
+ --bd_flushto;
+ if (bd_flushto >= numdirtybuffers - 5) {
+ bd_flushto = numdirtybuffers - 10;
+ bd_flushinc = 1;
+ }
+ if (bd_flushto < 2)
+ bd_flushto = 2;
+ } else {
+ /*
+ * We slept and timed out, we can slow down.
+ */
+ bd_flushto += bd_flushinc;
+ if (bd_flushto > hidirtybuffers)
+ bd_flushto = hidirtybuffers;
+ ++bd_flushinc;
+ if (bd_flushinc > hidirtybuffers / 20 + 1)
+ bd_flushinc = hidirtybuffers / 20 + 1;
+ }
/*
- * We calculate how much to add or subtract from bd_flushto
- * and bd_interval based on how far off we are from the
- * optimal number of dirty buffers, which is 20% below the
- * hidirtybuffers mark. We cannot use hidirtybuffers straight
- * because being right on the mark will cause getnewbuf()
- * to oscillate our wakeup.
- *
- * The larger the error in either direction, the more we adjust
- * bd_flushto and bd_interval. The time interval is adjusted
- * by 2 seconds per whole-buffer-range of error. This is an
- * exponential convergence algorithm, with large errors
- * producing large changes and small errors producing small
- * changes.
+ * Set the interval on a linear scale based on hidirtybuffers
+ * with a maximum frequency of 1/10 second.
*/
-
- {
- int brange = hidirtybuffers - lodirtybuffers;
- int middb = hidirtybuffers - brange / 5;
- int deltabuf = middb - numdirtybuffers;
-
- bd_flushto += deltabuf / 20;
- bd_interval += deltabuf * (2 * hz) / (brange * 1);
- }
- if (bd_flushto < lodirtybuffers)
- bd_flushto = lodirtybuffers;
- if (bd_flushto > hidirtybuffers)
- bd_flushto = hidirtybuffers;
+ bd_interval = bd_flushto * 5 * hz / hidirtybuffers;
if (bd_interval < hz / 10)
bd_interval = hz / 10;
- if (bd_interval > 5 * hz)
- bd_interval = 5 * hz;
}
}
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