X-Git-Url: https://git.liburcu.org/?p=urcu.git;a=blobdiff_plain;f=urcu-qsbr.c;h=5b341b5cfd6d97034b08ca5ea6df913a0c8a7736;hp=d3a6849ac04901097783fd0810b7a4aba4bf792c;hb=bcc74df39fa57a21aa977ef14e02ed8ab13c37e2;hpb=4a6d73787de534cbd7d5fc7a6b60af64de66e7ea diff --git a/urcu-qsbr.c b/urcu-qsbr.c index d3a6849..5b341b5 100644 --- a/urcu-qsbr.c +++ b/urcu-qsbr.c @@ -35,7 +35,7 @@ #include #include -#include "urcu/wfqueue.h" +#include "urcu/wfcqueue.h" #include "urcu/map/urcu-qsbr.h" #define BUILD_QSBR_LIB #include "urcu/static/urcu-qsbr.h" @@ -53,7 +53,7 @@ void __attribute__((destructor)) rcu_exit(void); static pthread_mutex_t rcu_gp_lock = PTHREAD_MUTEX_INITIALIZER; -int32_t gp_futex; +int32_t rcu_gp_futex; /* * Global grace period counter. @@ -72,8 +72,8 @@ unsigned long rcu_gp_ctr = RCU_GP_ONLINE; DEFINE_URCU_TLS(struct rcu_reader, rcu_reader); #ifdef DEBUG_YIELD -unsigned int yield_active; -DEFINE_URCU_TLS(unsigned int, rand_yield); +unsigned int rcu_yield_active; +DEFINE_URCU_TLS(unsigned int, rcu_rand_yield); #endif static CDS_LIST_HEAD(registry); @@ -111,69 +111,66 @@ static void wait_gp(void) { /* Read reader_gp before read futex */ cmm_smp_rmb(); - if (uatomic_read(&gp_futex) == -1) - futex_noasync(&gp_futex, FUTEX_WAIT, -1, + if (uatomic_read(&rcu_gp_futex) == -1) + futex_noasync(&rcu_gp_futex, FUTEX_WAIT, -1, NULL, NULL, 0); } -static void update_counter_and_wait(void) +static void wait_for_readers(struct cds_list_head *input_readers, + struct cds_list_head *cur_snap_readers, + struct cds_list_head *qsreaders) { - CDS_LIST_HEAD(qsreaders); int wait_loops = 0; struct rcu_reader *index, *tmp; -#if (CAA_BITS_PER_LONG < 64) - /* Switch parity: 0 -> 1, 1 -> 0 */ - CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); -#else /* !(CAA_BITS_PER_LONG < 64) */ - /* Increment current G.P. */ - CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); -#endif /* !(CAA_BITS_PER_LONG < 64) */ - - /* - * Must commit rcu_gp_ctr update to memory before waiting for - * quiescent state. Failure to do so could result in the writer - * waiting forever while new readers are always accessing data - * (no progress). Enforce compiler-order of store to rcu_gp_ctr - * before load URCU_TLS(rcu_reader).ctr. - */ - cmm_barrier(); - - /* - * Adding a cmm_smp_mb() which is _not_ formally required, but makes the - * model easier to understand. It does not have a big performance impact - * anyway, given this is the write-side. - */ - cmm_smp_mb(); - /* - * Wait for each thread rcu_reader_qs_gp count to become 0. + * Wait for each thread URCU_TLS(rcu_reader).ctr to either + * indicate quiescence (offline), or for them to observe the + * current rcu_gp_ctr value. */ for (;;) { wait_loops++; if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { - uatomic_set(&gp_futex, -1); + uatomic_set(&rcu_gp_futex, -1); /* * Write futex before write waiting (the other side * reads them in the opposite order). */ cmm_smp_wmb(); - cds_list_for_each_entry(index, ®istry, node) { + cds_list_for_each_entry(index, input_readers, node) { _CMM_STORE_SHARED(index->waiting, 1); } /* Write futex before read reader_gp */ cmm_smp_mb(); } - cds_list_for_each_entry_safe(index, tmp, ®istry, node) { - if (!rcu_gp_ongoing(&index->ctr)) - cds_list_move(&index->node, &qsreaders); + cds_list_for_each_entry_safe(index, tmp, input_readers, node) { + switch (rcu_reader_state(&index->ctr)) { + case RCU_READER_ACTIVE_CURRENT: + if (cur_snap_readers) { + cds_list_move(&index->node, + cur_snap_readers); + break; + } + /* Fall-through */ + case RCU_READER_INACTIVE: + cds_list_move(&index->node, qsreaders); + break; + case RCU_READER_ACTIVE_OLD: + /* + * Old snapshot. Leaving node in + * input_readers will make us busy-loop + * until the snapshot becomes current or + * the reader becomes inactive. + */ + break; + } } - if (cds_list_empty(®istry)) { + if (cds_list_empty(input_readers)) { if (wait_loops >= RCU_QS_ACTIVE_ATTEMPTS) { /* Read reader_gp before write futex */ cmm_smp_mb(); - uatomic_set(&gp_futex, 0); + uatomic_set(&rcu_gp_futex, 0); } break; } else { @@ -188,8 +185,6 @@ static void update_counter_and_wait(void) } } } - /* put back the reader list in the registry */ - cds_list_splice(&qsreaders, ®istry); } /* @@ -200,6 +195,8 @@ static void update_counter_and_wait(void) #if (CAA_BITS_PER_LONG < 64) void synchronize_rcu(void) { + CDS_LIST_HEAD(cur_snap_readers); + CDS_LIST_HEAD(qsreaders); unsigned long was_online; was_online = URCU_TLS(rcu_reader).ctr; @@ -223,17 +220,36 @@ void synchronize_rcu(void) goto out; /* - * Wait for previous parity to be empty of readers. + * Wait for readers to observe original parity or be quiescent. */ - update_counter_and_wait(); /* 0 -> 1, wait readers in parity 0 */ + wait_for_readers(®istry, &cur_snap_readers, &qsreaders); /* - * Must finish waiting for quiescent state for parity 0 before - * committing next rcu_gp_ctr update to memory. Failure to - * do so could result in the writer waiting forever while new + * Must finish waiting for quiescent state for original parity + * before committing next rcu_gp_ctr update to memory. Failure + * to do so could result in the writer waiting forever while new * readers are always accessing data (no progress). Enforce - * compiler-order of load URCU_TLS(rcu_reader).ctr before store to - * rcu_gp_ctr. + * compiler-order of load URCU_TLS(rcu_reader).ctr before store + * to rcu_gp_ctr. + */ + cmm_barrier(); + + /* + * Adding a cmm_smp_mb() which is _not_ formally required, but makes the + * model easier to understand. It does not have a big performance impact + * anyway, given this is the write-side. + */ + cmm_smp_mb(); + + /* Switch parity: 0 -> 1, 1 -> 0 */ + CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr ^ RCU_GP_CTR); + + /* + * Must commit rcu_gp_ctr update to memory before waiting for + * quiescent state. Failure to do so could result in the writer + * waiting forever while new readers are always accessing data + * (no progress). Enforce compiler-order of store to rcu_gp_ctr + * before load URCU_TLS(rcu_reader).ctr. */ cmm_barrier(); @@ -245,9 +261,14 @@ void synchronize_rcu(void) cmm_smp_mb(); /* - * Wait for previous parity to be empty of readers. + * Wait for readers to observe new parity or be quiescent. + */ + wait_for_readers(&cur_snap_readers, NULL, &qsreaders); + + /* + * Put quiescent reader list back into registry. */ - update_counter_and_wait(); /* 1 -> 0, wait readers in parity 1 */ + cds_list_splice(&qsreaders, ®istry); out: mutex_unlock(&rcu_gp_lock); @@ -263,6 +284,7 @@ out: #else /* !(CAA_BITS_PER_LONG < 64) */ void synchronize_rcu(void) { + CDS_LIST_HEAD(qsreaders); unsigned long was_online; was_online = URCU_TLS(rcu_reader).ctr; @@ -280,7 +302,35 @@ void synchronize_rcu(void) mutex_lock(&rcu_gp_lock); if (cds_list_empty(®istry)) goto out; - update_counter_and_wait(); + + /* Increment current G.P. */ + CMM_STORE_SHARED(rcu_gp_ctr, rcu_gp_ctr + RCU_GP_CTR); + + /* + * Must commit rcu_gp_ctr update to memory before waiting for + * quiescent state. Failure to do so could result in the writer + * waiting forever while new readers are always accessing data + * (no progress). Enforce compiler-order of store to rcu_gp_ctr + * before load URCU_TLS(rcu_reader).ctr. + */ + cmm_barrier(); + + /* + * Adding a cmm_smp_mb() which is _not_ formally required, but makes the + * model easier to understand. It does not have a big performance impact + * anyway, given this is the write-side. + */ + cmm_smp_mb(); + + /* + * Wait for readers to observe new count of be quiescent. + */ + wait_for_readers(®istry, NULL, &qsreaders); + + /* + * Put quiescent reader list back into registry. + */ + cds_list_splice(&qsreaders, ®istry); out: mutex_unlock(&rcu_gp_lock);