Commit 316580b6 authored by Eric Dumazet's avatar Eric Dumazet Committed by David S. Miller
Browse files

u64_stats: provide u64_stats_t type 



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: default avatarEric Dumazet <edumazet@google.com>
Signed-off-by: default avatarDavid S. Miller <davem@davemloft.net>
parent 4a43b1f9

include/linux/u64_stats_sync.h

+47 −4
Original line number Diff line number Diff line
@@ -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)

{

CRA Git | Maintained and supported by SUSTech CRA and CCSE