Author: hselasky
Date: Sat Nov 29 05:08:29 2014
New Revision: 275231
URL: https://svnweb.freebsd.org/changeset/base/275231
Log:
MFC r274017, r274088 and r275205:
Provide an on-stack temporary buffer for small IOCTL requests.
Avoiding a memory allocation per IOCTL request can give a significant
speedup for applications which heavily rely on IOCTLs.
Modified:
stable/9/sys/kern/sys_generic.c
Directory Properties:
stable/9/sys/ (props changed)
Modified: stable/9/sys/kern/sys_generic.c
==============================================================================
--- stable/9/sys/kern/sys_generic.c Sat Nov 29 05:07:24 2014
(r275230)
+++ stable/9/sys/kern/sys_generic.c Sat Nov 29 05:08:29 2014
(r275231)
@@ -74,6 +74,20 @@ __FBSDID("$FreeBSD$");
#include <security/audit/audit.h>
+/*
+ * The following macro defines how many bytes will be allocated from
+ * the stack instead of memory allocated when passing the IOCTL data
+ * structures from userspace and to the kernel. Some IOCTLs having
+ * small data structures are used very frequently and this small
+ * buffer on the stack gives a significant speedup improvement for
+ * those requests. The value of this define should be greater or equal
+ * to 64 bytes and should also be power of two. The data structure is
+ * currently hard-aligned to a 8-byte boundary on the stack. This
+ * should currently be sufficient for all supported platforms.
+ */
+#define SYS_IOCTL_SMALL_SIZE 128 /* bytes */
+#define SYS_IOCTL_SMALL_ALIGN 8 /* bytes */
+
int iosize_max_clamp = 1;
SYSCTL_INT(_debug, OID_AUTO, iosize_max_clamp, CTLFLAG_RW,
&iosize_max_clamp, 0, "Clamp max i/o size to INT_MAX");
@@ -640,6 +654,7 @@ struct ioctl_args {
int
sys_ioctl(struct thread *td, struct ioctl_args *uap)
{
+ u_char smalldata[SYS_IOCTL_SMALL_SIZE] __aligned(SYS_IOCTL_SMALL_ALIGN);
u_long com;
int arg, error;
u_int size;
@@ -674,17 +689,18 @@ sys_ioctl(struct thread *td, struct ioct
arg = (intptr_t)uap->data;
data = (void *)&arg;
size = 0;
- } else
- data = malloc((u_long)size, M_IOCTLOPS, M_WAITOK);
+ } else {
+ if (size > SYS_IOCTL_SMALL_SIZE)
+ data = malloc((u_long)size, M_IOCTLOPS,
M_WAITOK);
+ else
+ data = smalldata;
+ }
} else
data = (void *)&uap->data;
if (com & IOC_IN) {
error = copyin(uap->data, data, (u_int)size);
- if (error) {
- if (size > 0)
- free(data, M_IOCTLOPS);
- return (error);
- }
+ if (error != 0)
+ goto out;
} else if (com & IOC_OUT) {
/*
* Zero the buffer so the user always
@@ -698,7 +714,8 @@ sys_ioctl(struct thread *td, struct ioct
if (error == 0 && (com & IOC_OUT))
error = copyout(data, uap->data, (u_int)size);
- if (size > 0)
+out:
+ if (size > SYS_IOCTL_SMALL_SIZE)
free(data, M_IOCTLOPS);
return (error);
}
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