mirror of
https://git.kernel.org/pub/scm/linux/kernel/git/stable/linux.git
synced 2024-09-04 01:49:36 +00:00
![Frederic Weisbecker](/assets/img/avatar_default.png)
Introduce light versions of u64_stats helpers for context where either preempt or IRQs are disabled. This way we can make this library usable by scheduler irqtime accounting which currenty implement its ad-hoc version. Signed-off-by: Frederic Weisbecker <fweisbec@gmail.com> Cc: Eric Dumazet <eric.dumazet@gmail.com> Cc: Linus Torvalds <torvalds@linux-foundation.org> Cc: Mike Galbraith <efault@gmx.de> Cc: Paolo Bonzini <pbonzini@redhat.com> Cc: Peter Zijlstra <peterz@infradead.org> Cc: Rik van Riel <riel@redhat.com> Cc: Thomas Gleixner <tglx@linutronix.de> Cc: Wanpeng Li <wanpeng.li@hotmail.com> Link: http://lkml.kernel.org/r/1474849761-12678-4-git-send-email-fweisbec@gmail.com Signed-off-by: Ingo Molnar <mingo@kernel.org>
165 lines
4.9 KiB
C
165 lines
4.9 KiB
C
#ifndef _LINUX_U64_STATS_SYNC_H
|
|
#define _LINUX_U64_STATS_SYNC_H
|
|
|
|
/*
|
|
* To properly implement 64bits network statistics on 32bit and 64bit hosts,
|
|
* we provide a synchronization point, that is a noop on 64bit or UP kernels.
|
|
*
|
|
* Key points :
|
|
* 1) Use a seqcount on SMP 32bits, with low overhead.
|
|
* 2) Whole thing is a noop on 64bit arches or UP kernels.
|
|
* 3) Write side must ensure mutual exclusion or one seqcount update could
|
|
* be lost, thus blocking readers forever.
|
|
* If this synchronization point is not a mutex, but a spinlock or
|
|
* spinlock_bh() or disable_bh() :
|
|
* 3.1) Write side should not sleep.
|
|
* 3.2) Write side should not allow preemption.
|
|
* 3.3) If applicable, interrupts should be disabled.
|
|
*
|
|
* 4) If reader fetches several counters, there is no guarantee the whole values
|
|
* are consistent (remember point 1) : this is a noop on 64bit arches anyway)
|
|
*
|
|
* 5) readers are allowed to sleep or be preempted/interrupted : They perform
|
|
* pure reads. But if they have to fetch many values, it's better to not allow
|
|
* preemptions/interruptions to avoid many retries.
|
|
*
|
|
* 6) If counter might be written by an interrupt, readers should block interrupts.
|
|
* (On UP, there is no seqcount_t protection, a reader allowing interrupts could
|
|
* read partial values)
|
|
*
|
|
* 7) For irq and softirq uses, readers can use u64_stats_fetch_begin_irq() and
|
|
* u64_stats_fetch_retry_irq() helpers
|
|
*
|
|
* Usage :
|
|
*
|
|
* Stats producer (writer) should use following template granted it already got
|
|
* an exclusive access to counters (a lock is already taken, or per cpu
|
|
* data is used [in a non preemptable context])
|
|
*
|
|
* 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_update_end(&stats->syncp);
|
|
*
|
|
* While a consumer (reader) should use following template to get consistent
|
|
* snapshot for each variable (but no guarantee on several ones)
|
|
*
|
|
* u64 tbytes, tpackets;
|
|
* unsigned int start;
|
|
*
|
|
* do {
|
|
* start = u64_stats_fetch_begin(&stats->syncp);
|
|
* tbytes = stats->bytes64; // non atomic operation
|
|
* tpackets = stats->packets64; // non atomic operation
|
|
* } while (u64_stats_fetch_retry(&stats->syncp, start));
|
|
*
|
|
*
|
|
* Example of use in drivers/net/loopback.c, using per_cpu containers,
|
|
* in BH disabled context.
|
|
*/
|
|
#include <linux/seqlock.h>
|
|
|
|
struct u64_stats_sync {
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
seqcount_t seq;
|
|
#endif
|
|
};
|
|
|
|
|
|
static inline void u64_stats_init(struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG == 32 && defined(CONFIG_SMP)
|
|
seqcount_init(&syncp->seq);
|
|
#endif
|
|
}
|
|
|
|
static inline void u64_stats_update_begin(struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
write_seqcount_begin(&syncp->seq);
|
|
#endif
|
|
}
|
|
|
|
static inline void u64_stats_update_end(struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
write_seqcount_end(&syncp->seq);
|
|
#endif
|
|
}
|
|
|
|
static inline void u64_stats_update_begin_raw(struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
raw_write_seqcount_begin(&syncp->seq);
|
|
#endif
|
|
}
|
|
|
|
static inline void u64_stats_update_end_raw(struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
raw_write_seqcount_end(&syncp->seq);
|
|
#endif
|
|
}
|
|
|
|
static inline unsigned int __u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
return read_seqcount_begin(&syncp->seq);
|
|
#else
|
|
return 0;
|
|
#endif
|
|
}
|
|
|
|
static inline unsigned int u64_stats_fetch_begin(const struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
|
|
preempt_disable();
|
|
#endif
|
|
return __u64_stats_fetch_begin(syncp);
|
|
}
|
|
|
|
static inline bool __u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
|
|
unsigned int start)
|
|
{
|
|
#if BITS_PER_LONG==32 && defined(CONFIG_SMP)
|
|
return read_seqcount_retry(&syncp->seq, start);
|
|
#else
|
|
return false;
|
|
#endif
|
|
}
|
|
|
|
static inline bool u64_stats_fetch_retry(const struct u64_stats_sync *syncp,
|
|
unsigned int start)
|
|
{
|
|
#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
|
|
preempt_enable();
|
|
#endif
|
|
return __u64_stats_fetch_retry(syncp, start);
|
|
}
|
|
|
|
/*
|
|
* In case irq handlers can update u64 counters, readers can use following helpers
|
|
* - SMP 32bit arches use seqcount protection, irq safe.
|
|
* - UP 32bit must disable irqs.
|
|
* - 64bit have no problem atomically reading u64 values, irq safe.
|
|
*/
|
|
static inline unsigned int u64_stats_fetch_begin_irq(const struct u64_stats_sync *syncp)
|
|
{
|
|
#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
|
|
local_irq_disable();
|
|
#endif
|
|
return __u64_stats_fetch_begin(syncp);
|
|
}
|
|
|
|
static inline bool u64_stats_fetch_retry_irq(const struct u64_stats_sync *syncp,
|
|
unsigned int start)
|
|
{
|
|
#if BITS_PER_LONG==32 && !defined(CONFIG_SMP)
|
|
local_irq_enable();
|
|
#endif
|
|
return __u64_stats_fetch_retry(syncp, start);
|
|
}
|
|
|
|
#endif /* _LINUX_U64_STATS_SYNC_H */
|