On Tue, Nov 04, 2014 at 11:29:49AM +0000, Hans Petter Selasky wrote:
> Author: hselasky
> Date: Tue Nov 4 11:29:49 2014
> New Revision: 274088
> URL: https://svnweb.freebsd.org/changeset/base/274088
>
> Log:
> Simplify logic a bit. Ensure data buffer is properly aligned,
> 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
>
> Modified:
> head/sys/kern/sys_generic.c
>
> Modified: head/sys/kern/sys_generic.c
> ==============================================================================
> --- head/sys/kern/sys_generic.c Tue Nov 4 10:25:52 2014
> (r274087)
> +++ head/sys/kern/sys_generic.c Tue Nov 4 11:29:49 2014
> (r274088)
> @@ -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);
Should not you align to word size instead?
Also maybe it would be beneficial to derive the limit from KSTACK_PAGES
(something silly like KSTACK_PAGES * 32 or something), which I believe would
address earlier complaints.
> 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 ioct
> 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 ioct
> 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);
> }
>
--
Mateusz Guzik <mjguzik gmail.com>
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