cpufreq: allocate long-lived buffer for handling of sysctl requests

At present the cpufreq sysctl handler for current level setting would
allocate and deallocate a temporary buffer of 24KB even to handle a
read-only query.  This puts unnecessary load on memory subsystem when
current level is checked frequently, e.g. when the likes of powerd
and system monitoring software are running.
Change the strategy to allocating a long-lived buffer for handling the
requests.

Reviewed by:	njl
MFC after:	2 weeks

1 files changed, 6 insertions, 7 deletions

diff --git a/sys/kern/kern_cpu.c b/sys/kern/kern_cpu.c
index 4c4f961..3429a0f 100644
--- a/sys/kern/kern_cpu.c
+++ b/sys/kern/kern_cpu.c
@@ -76,6 +76,7 @@ struct cpufreq_softc {
 	device_t			dev;
 	struct sysctl_ctx_list		sysctl_ctx;
 	struct task			startup_task;
+	struct cf_level			*levels_buf;
 };
 
 struct cf_setting_array {
@@ -180,6 +181,8 @@ cpufreq_attach(device_t dev)
 
 	CF_DEBUG("initializing one-time data for %s\n",
 	    device_get_nameunit(dev));
+	sc->levels_buf = malloc(CF_MAX_LEVELS * sizeof(*sc->levels_buf),
+	    M_DEVBUF, M_WAITOK);
 	SYSCTL_ADD_PROC(&sc->sysctl_ctx,
 	    SYSCTL_CHILDREN(device_get_sysctl_tree(parent)),
 	    OID_AUTO, "freq", CTLTYPE_INT | CTLFLAG_RW, sc, 0,
@@ -227,6 +230,7 @@ cpufreq_detach(device_t dev)
 	numdevs = devclass_get_count(cpufreq_dc);
 	if (numdevs == 1) {
 		CF_DEBUG("final shutdown for %s\n", device_get_nameunit(dev));
+		free(sc->levels_buf, M_DEVBUF);
 	}
 
 	return (0);
@@ -870,9 +874,7 @@ cpufreq_curr_sysctl(SYSCTL_HANDLER_ARGS)
 
 	devs = NULL;
 	sc = oidp->oid_arg1;
-	levels = malloc(CF_MAX_LEVELS * sizeof(*levels), M_TEMP, M_NOWAIT);
-	if (levels == NULL)
-		return (ENOMEM);
+	levels = sc->levels_buf;
 
 	error = CPUFREQ_GET(sc->dev, &levels[0]);
 	if (error)
@@ -915,8 +917,6 @@ cpufreq_curr_sysctl(SYSCTL_HANDLER_ARGS)
 out:
 	if (devs)
 		free(devs, M_TEMP);
-	if (levels)
-		free(levels, M_TEMP);
 	return (error);
 }
 
@@ -934,7 +934,7 @@ cpufreq_levels_sysctl(SYSCTL_HANDLER_ARGS)
 
 	/* Get settings from the device and generate the output string. */
 	count = CF_MAX_LEVELS;
-	levels = malloc(count * sizeof(*levels), M_TEMP, M_NOWAIT);
+	levels = sc->levels_buf;
 	if (levels == NULL) {
 		sbuf_delete(&sb);
 		return (ENOMEM);
@@ -957,7 +957,6 @@ cpufreq_levels_sysctl(SYSCTL_HANDLER_ARGS)
 	error = sysctl_handle_string(oidp, sbuf_data(&sb), sbuf_len(&sb), req);
 
 out:
-	free(levels, M_TEMP);
 	sbuf_delete(&sb);
 	return (error);
 }