Date: Sat, 24 Sep 2011 20:17:04 GMT From: Arnaud Lacombe <lacombar@gmail.com> To: freebsd-gnats-submit@FreeBSD.org Subject: kern/160994: buf_ring(9): MD assumption in MI code Message-ID: <201109242017.p8OKH4Bc086659@red.freebsd.org> Resent-Message-ID: <201109242020.p8OKKBOv064234@freefall.freebsd.org>
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>Number: 160994
>Category: kern
>Synopsis: buf_ring(9): MD assumption in MI code
>Confidential: no
>Severity: non-critical
>Priority: low
>Responsible: freebsd-bugs
>State: open
>Quarter:
>Keywords:
>Date-Required:
>Class: sw-bug
>Submitter-Id: current-users
>Arrival-Date: Sat Sep 24 20:20:11 UTC 2011
>Closed-Date:
>Last-Modified:
>Originator: Arnaud Lacombe
>Release:
>Organization:
n/a
>Environment:
>Description:
`struct buf_ring', defined in `sys/sys/buf_ring.h' 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];
};
is making an MD guess, the amount of padding to fit the size of a cache line, in MI API. It should be replaced by gcc's __aligned(CACHE_LINE_SIZE) as it is currently wasting space on architecture with 64bytes-long cache line.
>How-To-Repeat:
>Fix:
>Release-Note:
>Audit-Trail:
>Unformatted:
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