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u64_stats: provide u64_stats_t type

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On 64bit arches, struct u64_stats_sync is empty and provides
no help against load/store tearing.

Using READ_ONCE()/WRITE_ONCE() would be needed.

But the update side would be slightly more expensive.

local64_t was defined so that we could use regular adds
in a manner which is atomic wrt IRQs.

However the u64_stats infra means we do not have to use
local64_t on 32bit arches since the syncp provides the needed
protection.

Signed-off-by: Eric Dumazet <edumazet@google.com>
Signed-off-by: David S. Miller <davem@davemloft.net>
This commit is contained in:
Eric Dumazet 2019-11-07 16:27:20 -08:00 committed by David S. Miller
parent 4a43b1f96b
commit 316580b69d
1 changed files with 47 additions and 4 deletions
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51
include/linux/u64_stats_sync.h
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@ -40,8 +40,8 @@
* spin_lock_bh(...) or other synchronization to get exclusive access
* ...
* u64_stats_update_begin(&stats->syncp);
* stats->bytes64 += len; // non atomic operation
* stats->packets64++; // non atomic operation
* u64_stats_add(&stats->bytes64, len); // non atomic operation
* u64_stats_inc(&stats->packets64); // non atomic operation
* u64_stats_update_end(&stats->syncp);
*
* While a consumer (reader) should use following template to get consistent
@ -52,8 +52,8 @@
*
* do {
* start = u64_stats_fetch_begin(&stats->syncp);
* tbytes = stats->bytes64; // non atomic operation
* tpackets = stats->packets64; // non atomic operation
* tbytes = u64_stats_read(&stats->bytes64); // non atomic operation
* tpackets = u64_stats_read(&stats->packets64); // non atomic operation
* } while (u64_stats_fetch_retry(&stats->syncp, start));
*
*
@ -68,6 +68,49 @@ struct u64_stats_sync {
#endif
};
#if BITS_PER_LONG == 64
#include <asm/local64.h>
typedef struct {
local64_t v;
} u64_stats_t ;
static inline u64 u64_stats_read(const u64_stats_t *p)
{
return local64_read(&p->v);
}
static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
{
local64_add(val, &p->v);
}
static inline void u64_stats_inc(u64_stats_t *p)
{
local64_inc(&p->v);
}
#else
typedef struct {
u64 v;
} u64_stats_t;
static inline u64 u64_stats_read(const u64_stats_t *p)
{
return p->v;
}
static inline void u64_stats_add(u64_stats_t *p, unsigned long val)
{
p->v += val;
}
static inline void u64_stats_inc(u64_stats_t *p)
{
p->v++;
}
#endif
static inline void u64_stats_init(struct u64_stats_sync *syncp)
{