* LTTng userspace tracer buffering system
*
* Copyright (C) 2009 - Pierre-Marc Fournier (pierre-marc dot fournier at polymtl dot ca)
- * Copyright (C) 2008 - Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca)
+ * Copyright (C) 2008-2011 - Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca)
*
* This library is free software; you can redistribute it and/or
* modify it under the terms of the GNU Lesser General Public
* Foundation, Inc., 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA
*/
+/*
+ * Note: this code does not support the ref/noref flag and reader-owned
+ * subbuffer scheme needed for flight recorder mode.
+ */
+
#include <unistd.h>
#include <sys/mman.h>
#include <sys/ipc.h>
static DEFINE_MUTEX(ust_buffers_channels_mutex);
static CDS_LIST_HEAD(ust_buffers_channels);
+static void ltt_force_switch(struct ust_buffer *buf,
+ enum force_switch_mode mode);
+
static int get_n_cpus(void)
{
int result;
return;
pthread_mutex_lock(&ust_buffers_channels_mutex);
- for(i=0; i<chan->n_cpus; i++) {
- /* FIXME: if we make it here, then all buffers were necessarily allocated. Moreover, we don't
- * initialize to NULL so we cannot use this check. Should we? */
-//ust// if (chan->buf[i])
+ /*
+ * checking for chan->buf[i] being NULL or not is useless in
+ * practice because we allocate buffers for all possible cpus.
+ * However, should we decide to change this and only allocate
+ * for online cpus, this check becomes useful.
+ */
+ for (i=0; i<chan->n_cpus; i++) {
+ if (chan->buf[i])
close_buf(chan->buf[i]);
}
pthread_mutex_unlock(&ust_buffers_channels_mutex);
}
-static void ltt_force_switch(struct ust_buffer *buf,
- enum force_switch_mode mode);
-
-
-
/*
* offset is assumed to never be 0 here : never deliver a completely empty
* subbuffer. The lost size is between 0 and subbuf_size-1.
* data and the write offset. Correct consumed offset ordering
* wrt commit count is insured by the use of cmpxchg to update
* the consumed offset.
- * smp_call_function_single can fail if the remote CPU is offline,
- * this is OK because then there is no wmb to execute there.
- * If our thread is executing on the same CPU as the on the buffers
- * belongs to, we don't have to synchronize it at all. If we are
- * migrated, the scheduler will take care of the memory cmm_barriers.
- * Normally, smp_call_function_single() should ensure program order when
- * executing the remote function, which implies that it surrounds the
- * function execution with :
- * smp_mb()
- * send IPI
- * csd_lock_wait
- * recv IPI
- * smp_mb()
- * exec. function
- * smp_mb()
- * csd unlock
- * smp_mb()
- *
- * However, smp_call_function_single() does not seem to clearly execute
- * such barriers. It depends on spinlock semantic to provide the barrier
- * before executing the IPI and, when busy-looping, csd_lock_wait only
- * executes smp_mb() when it has to wait for the other CPU.
- *
- * I don't trust this code. Therefore, let's add the smp_mb() sequence
- * required ourself, even if duplicated. It has no performance impact
- * anyway.
- *
- * smp_mb() is needed because cmm_smp_rmb() and cmm_smp_wmb() only order read vs
- * read and write vs write. They do not ensure core synchronization. We
- * really have to ensure total order between the 3 cmm_barriers running on
- * the 2 CPUs.
*/
-//ust// #ifdef LTT_NO_IPI_BARRIER
+
/*
* Local rmb to match the remote wmb to read the commit count before the
* buffer data and the write offset.
*/
cmm_smp_rmb();
-//ust// #else
-//ust// if (raw_smp_processor_id() != buf->cpu) {
-//ust// smp_mb(); /* Total order with IPI handler smp_mb() */
-//ust// smp_call_function_single(buf->cpu, remote_mb, NULL, 1);
-//ust// smp_mb(); /* Total order with IPI handler smp_mb() */
-//ust// }
-//ust// #endif
write_offset = uatomic_read(&buf->offset);
/*
== 0) {
return -EAGAIN;
}
-
- /* FIXME: is this ok to disable the reading feature? */
-//ust// retval = update_read_sb_index(buf, consumed_idx);
-//ust// if (retval)
-//ust// return retval;
-
*consumed = consumed_old;
return 0;
consumed_old = consumed_old | uconsumed_old;
consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);
-//ust// spin_lock(<t_buf->full_lock);
if (uatomic_cmpxchg(&buf->consumed, consumed_old,
consumed_new)
!= consumed_old) {
/* We have been pushed by the writer : the last
* buffer read _is_ corrupted! It can also
* happen if this is a buffer we never got. */
-//ust// spin_unlock(<t_buf->full_lock);
return -EIO;
} else {
/* tell the client that buffer is now unfull */
index = SUBBUF_INDEX(consumed_old, buf->chan);
data = BUFFER_OFFSET(consumed_old, buf->chan);
ltt_buf_unfull(buf, index, data);
-//ust// spin_unlock(<t_buf->full_lock);
}
return 0;
}
static void ltt_relay_async_wakeup_chan(struct ust_channel *ltt_channel)
{
-//ust// unsigned int i;
-//ust// struct rchan *rchan = ltt_channel->trans_channel_data;
-//ust//
-//ust// for_each_possible_cpu(i) {
-//ust// struct ltt_channel_buf_struct *ltt_buf =
-//ust// percpu_ptr(ltt_channel->buf, i);
-//ust//
-//ust// if (uatomic_read(<t_buf->wakeup_readers) == 1) {
-//ust// uatomic_set(<t_buf->wakeup_readers, 0);
-//ust// wake_up_interruptible(&rchan->buf[i]->read_wait);
-//ust// }
-//ust// }
}
static void ltt_relay_finish_buffer(struct ust_channel *channel, unsigned int cpu)
{
-// int result;
-
if (channel->buf[cpu]) {
struct ust_buffer *buf = channel->buf[cpu];
ltt_force_switch(buf, FORCE_FLUSH);
{
unsigned int i;
- for(i=0; i<channel->n_cpus; i++) {
+ for (i=0; i<channel->n_cpus; i++) {
ltt_relay_finish_buffer(channel, i);
}
}
*/
if (mode == FORCE_ACTIVE) {
ltt_reserve_push_reader(chan, buf, offsets.end - 1);
-//ust// ltt_clear_noref_flag(chan, buf, SUBBUF_INDEX(offsets.end - 1, chan));
}
/*
* Switch old subbuffer if needed.
*/
if (offsets.end_switch_old) {
-//ust// ltt_clear_noref_flag(rchan, buf, SUBBUF_INDEX(offsets.old - 1, rchan));
ltt_reserve_switch_old_subbuf(chan, buf, &offsets, &tsc);
}
*/
ltt_reserve_push_reader(chan, buf, offsets.end - 1);
- /*
- * Clear noref flag for this subbuffer.
- */
-//ust// ltt_clear_noref_flag(chan, buf, SUBBUF_INDEX(offsets.end - 1, chan));
-
/*
* Switch old subbuffer if needed.
*/
if (unlikely(offsets.end_switch_old)) {
-//ust// ltt_clear_noref_flag(chan, buf, SUBBUF_INDEX(offsets.old - 1, chan));
ltt_reserve_switch_old_subbuf(chan, buf, &offsets, tsc);
DBG("Switching %s_%d", chan->channel_name, cpu);
}
projects / ust.git / blobdiff