svn commit: r274088 - head/sys/kern

[Adrian Chadd]

... why not just use UMA?


-adrian

On 4 November 2014 03:29, Hans Petter Selasky <hselasky at freebsd.org> 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);
>         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);
>  }
>