Hi,
On Wed, Sep 14, 2011 at 10:53 PM, Arnaud Lacombe <lacom...@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' ?
>
> 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;
shouldn't those 3 fields be updated atomically, especially on 32bits
platforms ? That might pose a problem as, AFAIK, FreeBSD do not have
MI 64bits atomics operations...
- Arnaud
> /*
> * 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).
>
> Thanks in advance,
> - Arnaud
>
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