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Simplify logic a bit. Ensure data buffer is properly aligned,

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especially for platforms where unaligned access is not allowed. Make
it possible to override the small buffer size.

A simple continuous read string test using libusb showed a reduction
in CPU usage from roughly 10% to less than 1% using a dual-core GHz
CPU, when the malloc() operation was skipped for small buffers.

MFC after:	2 weeks
This commit is contained in:
Hans Petter Selasky 2014-11-04 11:29:49 +00:00
parent 038263c36a
commit 0ecd606b24
1 changed files with 8 additions and 5 deletions
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13
sys/kern/sys_generic.c
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@ -646,10 +646,13 @@ struct ioctl_args {
int
sys_ioctl(struct thread *td, struct ioctl_args *uap)
{
#ifndef SYS_IOCTL_SMALL_SIZE
#define SYS_IOCTL_SMALL_SIZE 128
#endif
u_char smalldata[SYS_IOCTL_SMALL_SIZE] __aligned(8);
u_long com;
int arg, error;
u_int size;
u_char smalldata[128];
caddr_t data;
if (uap->com > 0xffffffff) {
@ -682,10 +685,10 @@ sys_ioctl(struct thread *td, struct ioctl_args *uap)
data = (void *)&arg;
size = 0;
} else {
if (size <= sizeof(smalldata))
data = smalldata;
else
if (size > SYS_IOCTL_SMALL_SIZE)
data = malloc((u_long)size, M_IOCTLOPS, M_WAITOK);
else
data = smalldata;
}
} else
data = (void *)&uap->data;
@ -707,7 +710,7 @@ sys_ioctl(struct thread *td, struct ioctl_args *uap)
error = copyout(data, uap->data, (u_int)size);
out:
if (size > 0 && data != (caddr_t)&smalldata)
if (size > SYS_IOCTL_SMALL_SIZE)
free(data, M_IOCTLOPS);
return (error);
}