From: Matthew Dillon <dillon@apollo.backplane.com>
Date: Tue, 3 Jul 2012 17:22:09 +0000 (-0700)
Subject: kernel - reduce kernel stack use
X-Git-Tag: v3.2.0~698
X-Git-Url: http://gitweb.dragonflybsd.org/dragonfly.git/commitdiff_plain/7c76e73a679321a9a4cc0a93178ee93fbda7aaa6

kernel - reduce kernel stack use

* fq_dispatcher() was eating 8K+ of kernel stack on x86-64 with a
  (512 x sizeof(pointer) * 2) sized array.  This is way too much kernel
  stack.

* Add a safety to the hz calculation in the lksleep() for hz values < 15.
  vkernels already use low hz values of ~20-ish.

Reported-by: swildner
---

diff --git a/sys/kern/dsched/fq/fq_core.c b/sys/kern/dsched/fq/fq_core.c
index e6128f3..6941500 100644
--- a/sys/kern/dsched/fq/fq_core.c
+++ b/sys/kern/dsched/fq/fq_core.c
@@ -65,7 +65,7 @@ extern struct dsched_policy dsched_fq_policy;
 void
 fq_dispatcher(struct fq_disk_ctx *diskctx)
 {
-	struct dispatch_prep dispatch_ary[FQ_DISPATCH_ARRAY_SZ];
+	struct dispatch_prep *dispatch_ary;
 	struct dsched_thread_io	*ds_tdio, *ds_tdio2;
 	struct fq_thread_io	*tdio;
 	struct bio *bio, *bio2;
@@ -73,6 +73,13 @@ fq_dispatcher(struct fq_disk_ctx *diskctx)
 	int i, prepd_io;
 
 	/*
+	 * Array is dangerously big for an on-stack declaration, allocate
+	 * it instead.
+	 */
+	dispatch_ary = kmalloc(sizeof(*dispatch_ary) * FQ_DISPATCH_ARRAY_SZ,
+			       M_TEMP, M_INTWAIT | M_ZERO);
+
+	/*
 	 * We need to manually assign an tdio to the tdctx of this thread
 	 * since it isn't assigned one during fq_prepare, as the disk
 	 * is not set up yet.
@@ -83,8 +90,11 @@ fq_dispatcher(struct fq_disk_ctx *diskctx)
 	DSCHED_DISK_CTX_LOCK(&diskctx->head);
 	for(;;) {
 		idle = 0;
-		/* sleep ~60 ms */
-		if ((lksleep(diskctx, &diskctx->head.lock, 0, "fq_dispatcher", hz/15) == 0)) {
+		/*
+		 * sleep ~60 ms, failsafe low hz rates.
+		 */
+		if ((lksleep(diskctx, &diskctx->head.lock, 0,
+			     "fq_dispatcher", (hz + 14) / 15) == 0)) {
 			/*
 			 * We've been woken up; this either means that we are
 			 * supposed to die away nicely or that the disk is idle.