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timer: relax barrier for status update

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Volatile has no ordering semantics. The rte_timer structure defines
timer status as a volatile variable and uses the rte_r/wmb barrier
to guarantee inter-thread visibility.

This patch optimized the volatile operation with c11 atomic operations
and one-way barrier to save the performance penalty. According to the
timer_perf_autotest benchmarking results, this patch can uplift 10%~16%
timer appending performance, 3%~20% timer resetting performance and 45%
timer callbacks scheduling performance on aarch64 and no loss in
performance for x86.

Suggested-by: Honnappa Nagarahalli <honnappa.nagarahalli@arm.com>
Signed-off-by: Phil Yang <phil.yang@arm.com>
Reviewed-by: Gavin Hu <gavin.hu@arm.com>
Acked-by: Erik Gabriel Carrillo <erik.g.carrillo@intel.com>
This commit is contained in:
Phil Yang 2020-04-26 22:45:15 +08:00 committed by Thomas Monjalon
parent 9ca37645c7
commit 2f89dc2ed7
1 changed files with 60 additions and 27 deletions
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87
lib/librte_timer/rte_timer.c
View File

@ -10,7 +10,6 @@
#include <assert.h>
#include <sys/queue.h>
#include <rte_atomic.h>
#include <rte_common.h>
#include <rte_cycles.h>
#include <rte_eal_memconfig.h>
@ -218,7 +217,7 @@ rte_timer_init(struct rte_timer *tim)
status.state = RTE_TIMER_STOP;
status.owner = RTE_TIMER_NO_OWNER;
tim->status.u32 = status.u32;
__atomic_store_n(&tim->status.u32, status.u32, __ATOMIC_RELAXED);
}
/*
@ -239,9 +238,9 @@ timer_set_config_state(struct rte_timer *tim,
/* wait that the timer is in correct status before update,
* and mark it as being configured */
while (success == 0) {
prev_status.u32 = tim->status.u32;
prev_status.u32 = __atomic_load_n(&tim->status.u32, __ATOMIC_RELAXED);
while (success == 0) {
/* timer is running on another core
* or ready to run on local core, exit
*/
@ -258,9 +257,15 @@ timer_set_config_state(struct rte_timer *tim,
* mark it atomically as being configured */
status.state = RTE_TIMER_CONFIG;
status.owner = (int16_t)lcore_id;
success = rte_atomic32_cmpset(&tim->status.u32,
prev_status.u32,
status.u32);
/* CONFIG states are acting as locked states. If the
* timer is in CONFIG state, the state cannot be changed
* by other threads. So, we should use ACQUIRE here.
*/
success = __atomic_compare_exchange_n(&tim->status.u32,
&prev_status.u32,
status.u32, 0,
__ATOMIC_ACQUIRE,
__ATOMIC_RELAXED);
}
ret_prev_status->u32 = prev_status.u32;
@ -279,20 +284,27 @@ timer_set_running_state(struct rte_timer *tim)
/* wait that the timer is in correct status before update,
* and mark it as running */
while (success == 0) {
prev_status.u32 = tim->status.u32;
prev_status.u32 = __atomic_load_n(&tim->status.u32, __ATOMIC_RELAXED);
while (success == 0) {
/* timer is not pending anymore */
if (prev_status.state != RTE_TIMER_PENDING)
return -1;
/* here, we know that timer is stopped or pending,
* mark it atomically as being configured */
/* we know that the timer will be pending at this point
* mark it atomically as being running
*/
status.state = RTE_TIMER_RUNNING;
status.owner = (int16_t)lcore_id;
success = rte_atomic32_cmpset(&tim->status.u32,
prev_status.u32,
status.u32);
/* RUNNING states are acting as locked states. If the
* timer is in RUNNING state, the state cannot be changed
* by other threads. So, we should use ACQUIRE here.
*/
success = __atomic_compare_exchange_n(&tim->status.u32,
&prev_status.u32,
status.u32, 0,
__ATOMIC_ACQUIRE,
__ATOMIC_RELAXED);
}
return 0;
@ -520,10 +532,12 @@ __rte_timer_reset(struct rte_timer *tim, uint64_t expire,
/* update state: as we are in CONFIG state, only us can modify
* the state so we don't need to use cmpset() here */
rte_wmb();
status.state = RTE_TIMER_PENDING;
status.owner = (int16_t)tim_lcore;
tim->status.u32 = status.u32;
/* The "RELEASE" ordering guarantees the memory operations above
* the status update are observed before the update by all threads
*/
__atomic_store_n(&tim->status.u32, status.u32, __ATOMIC_RELEASE);
if (tim_lcore != lcore_id || !local_is_locked)
rte_spinlock_unlock(&priv_timer[tim_lcore].list_lock);
@ -600,10 +614,12 @@ __rte_timer_stop(struct rte_timer *tim, int local_is_locked,
}
/* mark timer as stopped */
rte_wmb();
status.state = RTE_TIMER_STOP;
status.owner = RTE_TIMER_NO_OWNER;
tim->status.u32 = status.u32;
/* The "RELEASE" ordering guarantees the memory operations above
* the status update are observed before the update by all threads
*/
__atomic_store_n(&tim->status.u32, status.u32, __ATOMIC_RELEASE);
return 0;
}
@ -637,7 +653,8 @@ rte_timer_stop_sync(struct rte_timer *tim)
int
rte_timer_pending(struct rte_timer *tim)
{
return tim->status.state == RTE_TIMER_PENDING;
return __atomic_load_n(&tim->status.state,
__ATOMIC_RELAXED) == RTE_TIMER_PENDING;
}
/* must be called periodically, run all timer that expired */
@ -739,8 +756,12 @@ __rte_timer_manage(struct rte_timer_data *timer_data)
/* remove from done list and mark timer as stopped */
status.state = RTE_TIMER_STOP;
status.owner = RTE_TIMER_NO_OWNER;
rte_wmb();
tim->status.u32 = status.u32;
/* The "RELEASE" ordering guarantees the memory
* operations above the status update are observed
* before the update by all threads
*/
__atomic_store_n(&tim->status.u32, status.u32,
__ATOMIC_RELEASE);
}
else {
/* keep it in list and mark timer as pending */
@ -748,8 +769,12 @@ __rte_timer_manage(struct rte_timer_data *timer_data)
status.state = RTE_TIMER_PENDING;
__TIMER_STAT_ADD(priv_timer, pending, 1);
status.owner = (int16_t)lcore_id;
rte_wmb();
tim->status.u32 = status.u32;
/* The "RELEASE" ordering guarantees the memory
* operations above the status update are observed
* before the update by all threads
*/
__atomic_store_n(&tim->status.u32, status.u32,
__ATOMIC_RELEASE);
__rte_timer_reset(tim, tim->expire + tim->period,
tim->period, lcore_id, tim->f, tim->arg, 1,
timer_data);
@ -919,8 +944,12 @@ rte_timer_alt_manage(uint32_t timer_data_id,
/* remove from done list and mark timer as stopped */
status.state = RTE_TIMER_STOP;
status.owner = RTE_TIMER_NO_OWNER;
rte_wmb();
tim->status.u32 = status.u32;
/* The "RELEASE" ordering guarantees the memory
* operations above the status update are observed
* before the update by all threads
*/
__atomic_store_n(&tim->status.u32, status.u32,
__ATOMIC_RELEASE);
} else {
/* keep it in list and mark timer as pending */
rte_spinlock_lock(
@ -928,8 +957,12 @@ rte_timer_alt_manage(uint32_t timer_data_id,
status.state = RTE_TIMER_PENDING;
__TIMER_STAT_ADD(data->priv_timer, pending, 1);
status.owner = (int16_t)this_lcore;
rte_wmb();
tim->status.u32 = status.u32;
/* The "RELEASE" ordering guarantees the memory
* operations above the status update are observed
* before the update by all threads
*/
__atomic_store_n(&tim->status.u32, status.u32,
__ATOMIC_RELEASE);
__rte_timer_reset(tim, tim->expire + tim->period,
tim->period, this_lcore, tim->f, tim->arg, 1,
data);