buf_ring(9) API precisions

[K. Macy]

On Thu, Sep 15, 2011 at 4:53 AM, Arnaud Lacombe <lacombar at gmail.com> wrote:
> Hi Kip,
>
> I've got a few question about the buf_ring(9) API.
>
> 1) what means the 'drbr_' prefix. I can guess the two last letter, 'b'
> and 'r', for Buffer Ring, but what about 'd' and 'r' ?

DRiver BufRing

> 2) in `sys/sys/buf_ring.h', you defined 'struct buf_ring' as:
>
> struct buf_ring {
>        volatile uint32_t       br_prod_head;
>        volatile uint32_t       br_prod_tail;
>        int                     br_prod_size;
>        int                     br_prod_mask;
>        uint64_t                br_drops;
>        uint64_t                br_prod_bufs;
>        uint64_t                br_prod_bytes;
>        /*
>         * Pad out to next L2 cache line
>         */
>        uint64_t                _pad0[11];
>
>        volatile uint32_t       br_cons_head;
>        volatile uint32_t       br_cons_tail;
>        int                     br_cons_size;
>        int                     br_cons_mask;
>
>        /*
>         * Pad out to next L2 cache line
>         */
>        uint64_t                _pad1[14];
> #ifdef DEBUG_BUFRING
>        struct mtx              *br_lock;
> #endif
>        void                    *br_ring[0];
> };
>
> Why are you making an MD guess, the amount of padding to fit the size
> of a cache line, in MI API ? Strangely enough, you did not make this
> assumption in, say r205488 (picked randomly).

It has been several years, and I haven't done any work in svn in over
a year, I don't remember. I probably meant to refine it in a later
iteration.

If you would like to send me a patch addressing this I'd be more than
happy to apply it if appropriate. Otherwise, I will deal with it some
time after 9 settles.

Thanks for pointing this out.

Cheers