--- /dev/null
+#ifndef _LINUX_RING_BUFFER_FRONTEND_INTERNAL_H
+#define _LINUX_RING_BUFFER_FRONTEND_INTERNAL_H
+
+/*
+ * linux/ringbuffer/frontend_internal.h
+ *
+ * (C) Copyright 2005-2010 - Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * Ring Buffer Library Synchronization Header (internal helpers).
+ *
+ * Author:
+ * Mathieu Desnoyers <mathieu.desnoyers@efficios.com>
+ *
+ * See ring_buffer_frontend.c for more information on wait-free algorithms.
+ *
+ * Dual LGPL v2.1/GPL v2 license.
+ */
+
+#include "../../wrapper/ringbuffer/config.h"
+#include "../../wrapper/ringbuffer/backend_types.h"
+#include "../../wrapper/ringbuffer/frontend_types.h"
+#include "../../lib/prio_heap/lttng_prio_heap.h" /* For per-CPU read-side iterator */
+
+/* Buffer offset macros */
+
+/* buf_trunc mask selects only the buffer number. */
+static inline
+unsigned long buf_trunc(unsigned long offset, struct channel *chan)
+{
+ return offset & ~(chan->backend.buf_size - 1);
+
+}
+
+/* Select the buffer number value (counter). */
+static inline
+unsigned long buf_trunc_val(unsigned long offset, struct channel *chan)
+{
+ return buf_trunc(offset, chan) >> chan->backend.buf_size_order;
+}
+
+/* buf_offset mask selects only the offset within the current buffer. */
+static inline
+unsigned long buf_offset(unsigned long offset, struct channel *chan)
+{
+ return offset & (chan->backend.buf_size - 1);
+}
+
+/* subbuf_offset mask selects the offset within the current subbuffer. */
+static inline
+unsigned long subbuf_offset(unsigned long offset, struct channel *chan)
+{
+ return offset & (chan->backend.subbuf_size - 1);
+}
+
+/* subbuf_trunc mask selects the subbuffer number. */
+static inline
+unsigned long subbuf_trunc(unsigned long offset, struct channel *chan)
+{
+ return offset & ~(chan->backend.subbuf_size - 1);
+}
+
+/* subbuf_align aligns the offset to the next subbuffer. */
+static inline
+unsigned long subbuf_align(unsigned long offset, struct channel *chan)
+{
+ return (offset + chan->backend.subbuf_size)
+ & ~(chan->backend.subbuf_size - 1);
+}
+
+/* subbuf_index returns the index of the current subbuffer within the buffer. */
+static inline
+unsigned long subbuf_index(unsigned long offset, struct channel *chan)
+{
+ return buf_offset(offset, chan) >> chan->backend.subbuf_size_order;
+}
+
+/*
+ * Last TSC comparison functions. Check if the current TSC overflows tsc_bits
+ * bits from the last TSC read. When overflows are detected, the full 64-bit
+ * timestamp counter should be written in the record header. Reads and writes
+ * last_tsc atomically.
+ */
+
+#if (BITS_PER_LONG == 32)
+static inline
+void save_last_tsc(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf, u64 tsc)
+{
+ if (config->tsc_bits == 0 || config->tsc_bits == 64)
+ return;
+
+ /*
+ * Ensure the compiler performs this update in a single instruction.
+ */
+ v_set(config, &buf->last_tsc, (unsigned long)(tsc >> config->tsc_bits));
+}
+
+static inline
+int last_tsc_overflow(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf, u64 tsc)
+{
+ unsigned long tsc_shifted;
+
+ if (config->tsc_bits == 0 || config->tsc_bits == 64)
+ return 0;
+
+ tsc_shifted = (unsigned long)(tsc >> config->tsc_bits);
+ if (unlikely(tsc_shifted
+ - (unsigned long)v_read(config, &buf->last_tsc)))
+ return 1;
+ else
+ return 0;
+}
+#else
+static inline
+void save_last_tsc(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf, u64 tsc)
+{
+ if (config->tsc_bits == 0 || config->tsc_bits == 64)
+ return;
+
+ v_set(config, &buf->last_tsc, (unsigned long)tsc);
+}
+
+static inline
+int last_tsc_overflow(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf, u64 tsc)
+{
+ if (config->tsc_bits == 0 || config->tsc_bits == 64)
+ return 0;
+
+ if (unlikely((tsc - v_read(config, &buf->last_tsc))
+ >> config->tsc_bits))
+ return 1;
+ else
+ return 0;
+}
+#endif
+
+extern
+int lib_ring_buffer_reserve_slow(struct lib_ring_buffer_ctx *ctx);
+
+extern
+void lib_ring_buffer_switch_slow(struct lib_ring_buffer *buf,
+ enum switch_mode mode);
+
+/* Buffer write helpers */
+
+static inline
+void lib_ring_buffer_reserve_push_reader(struct lib_ring_buffer *buf,
+ struct channel *chan,
+ unsigned long offset)
+{
+ unsigned long consumed_old, consumed_new;
+
+ do {
+ consumed_old = atomic_long_read(&buf->consumed);
+ /*
+ * If buffer is in overwrite mode, push the reader consumed
+ * count if the write position has reached it and we are not
+ * at the first iteration (don't push the reader farther than
+ * the writer). This operation can be done concurrently by many
+ * writers in the same buffer, the writer being at the farthest
+ * write position sub-buffer index in the buffer being the one
+ * which will win this loop.
+ */
+ if (unlikely(subbuf_trunc(offset, chan)
+ - subbuf_trunc(consumed_old, chan)
+ >= chan->backend.buf_size))
+ consumed_new = subbuf_align(consumed_old, chan);
+ else
+ return;
+ } while (unlikely(atomic_long_cmpxchg(&buf->consumed, consumed_old,
+ consumed_new) != consumed_old));
+}
+
+static inline
+void lib_ring_buffer_vmcore_check_deliver(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ unsigned long commit_count,
+ unsigned long idx)
+{
+ if (config->oops == RING_BUFFER_OOPS_CONSISTENCY)
+ v_set(config, &buf->commit_hot[idx].seq, commit_count);
+}
+
+static inline
+int lib_ring_buffer_poll_deliver(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ struct channel *chan)
+{
+ unsigned long consumed_old, consumed_idx, commit_count, write_offset;
+
+ consumed_old = atomic_long_read(&buf->consumed);
+ consumed_idx = subbuf_index(consumed_old, chan);
+ commit_count = v_read(config, &buf->commit_cold[consumed_idx].cc_sb);
+ /*
+ * No memory barrier here, since we are only interested
+ * in a statistically correct polling result. The next poll will
+ * get the data is we are racing. The mb() that ensures correct
+ * memory order is in get_subbuf.
+ */
+ write_offset = v_read(config, &buf->offset);
+
+ /*
+ * Check that the subbuffer we are trying to consume has been
+ * already fully committed.
+ */
+
+ if (((commit_count - chan->backend.subbuf_size)
+ & chan->commit_count_mask)
+ - (buf_trunc(consumed_old, chan)
+ >> chan->backend.num_subbuf_order)
+ != 0)
+ return 0;
+
+ /*
+ * Check that we are not about to read the same subbuffer in
+ * which the writer head is.
+ */
+ if (subbuf_trunc(write_offset, chan) - subbuf_trunc(consumed_old, chan)
+ == 0)
+ return 0;
+
+ return 1;
+
+}
+
+static inline
+int lib_ring_buffer_pending_data(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ struct channel *chan)
+{
+ return !!subbuf_offset(v_read(config, &buf->offset), chan);
+}
+
+static inline
+unsigned long lib_ring_buffer_get_data_size(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ unsigned long idx)
+{
+ return subbuffer_get_data_size(config, &buf->backend, idx);
+}
+
+/*
+ * Check if all space reservation in a buffer have been committed. This helps
+ * knowing if an execution context is nested (for per-cpu buffers only).
+ * This is a very specific ftrace use-case, so we keep this as "internal" API.
+ */
+static inline
+int lib_ring_buffer_reserve_committed(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ struct channel *chan)
+{
+ unsigned long offset, idx, commit_count;
+
+ CHAN_WARN_ON(chan, config->alloc != RING_BUFFER_ALLOC_PER_CPU);
+ CHAN_WARN_ON(chan, config->sync != RING_BUFFER_SYNC_PER_CPU);
+
+ /*
+ * Read offset and commit count in a loop so they are both read
+ * atomically wrt interrupts. By deal with interrupt concurrency by
+ * restarting both reads if the offset has been pushed. Note that given
+ * we only have to deal with interrupt concurrency here, an interrupt
+ * modifying the commit count will also modify "offset", so it is safe
+ * to only check for offset modifications.
+ */
+ do {
+ offset = v_read(config, &buf->offset);
+ idx = subbuf_index(offset, chan);
+ commit_count = v_read(config, &buf->commit_hot[idx].cc);
+ } while (offset != v_read(config, &buf->offset));
+
+ return ((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
+ - (commit_count & chan->commit_count_mask) == 0);
+}
+
+static inline
+void lib_ring_buffer_check_deliver(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ struct channel *chan,
+ unsigned long offset,
+ unsigned long commit_count,
+ unsigned long idx)
+{
+ unsigned long old_commit_count = commit_count
+ - chan->backend.subbuf_size;
+ u64 tsc;
+
+ /* Check if all commits have been done */
+ if (unlikely((buf_trunc(offset, chan) >> chan->backend.num_subbuf_order)
+ - (old_commit_count & chan->commit_count_mask) == 0)) {
+ /*
+ * If we succeeded at updating cc_sb below, we are the subbuffer
+ * writer delivering the subbuffer. Deals with concurrent
+ * updates of the "cc" value without adding a add_return atomic
+ * operation to the fast path.
+ *
+ * We are doing the delivery in two steps:
+ * - First, we cmpxchg() cc_sb to the new value
+ * old_commit_count + 1. This ensures that we are the only
+ * subbuffer user successfully filling the subbuffer, but we
+ * do _not_ set the cc_sb value to "commit_count" yet.
+ * Therefore, other writers that would wrap around the ring
+ * buffer and try to start writing to our subbuffer would
+ * have to drop records, because it would appear as
+ * non-filled.
+ * We therefore have exclusive access to the subbuffer control
+ * structures. This mutual exclusion with other writers is
+ * crucially important to perform record overruns count in
+ * flight recorder mode locklessly.
+ * - When we are ready to release the subbuffer (either for
+ * reading or for overrun by other writers), we simply set the
+ * cc_sb value to "commit_count" and perform delivery.
+ *
+ * The subbuffer size is least 2 bytes (minimum size: 1 page).
+ * This guarantees that old_commit_count + 1 != commit_count.
+ */
+ if (likely(v_cmpxchg(config, &buf->commit_cold[idx].cc_sb,
+ old_commit_count, old_commit_count + 1)
+ == old_commit_count)) {
+ /*
+ * Start of exclusive subbuffer access. We are
+ * guaranteed to be the last writer in this subbuffer
+ * and any other writer trying to access this subbuffer
+ * in this state is required to drop records.
+ */
+ tsc = config->cb.ring_buffer_clock_read(chan);
+ v_add(config,
+ subbuffer_get_records_count(config,
+ &buf->backend, idx),
+ &buf->records_count);
+ v_add(config,
+ subbuffer_count_records_overrun(config,
+ &buf->backend,
+ idx),
+ &buf->records_overrun);
+ config->cb.buffer_end(buf, tsc, idx,
+ lib_ring_buffer_get_data_size(config,
+ buf,
+ idx));
+
+ /*
+ * Set noref flag and offset for this subbuffer id.
+ * Contains a memory barrier that ensures counter stores
+ * are ordered before set noref and offset.
+ */
+ lib_ring_buffer_set_noref_offset(config, &buf->backend, idx,
+ buf_trunc_val(offset, chan));
+
+ /*
+ * Order set_noref and record counter updates before the
+ * end of subbuffer exclusive access. Orders with
+ * respect to writers coming into the subbuffer after
+ * wrap around, and also order wrt concurrent readers.
+ */
+ smp_mb();
+ /* End of exclusive subbuffer access */
+ v_set(config, &buf->commit_cold[idx].cc_sb,
+ commit_count);
+ lib_ring_buffer_vmcore_check_deliver(config, buf,
+ commit_count, idx);
+
+ /*
+ * RING_BUFFER_WAKEUP_BY_WRITER wakeup is not lock-free.
+ */
+ if (config->wakeup == RING_BUFFER_WAKEUP_BY_WRITER
+ && atomic_long_read(&buf->active_readers)
+ && lib_ring_buffer_poll_deliver(config, buf, chan)) {
+ wake_up_interruptible(&buf->read_wait);
+ wake_up_interruptible(&chan->read_wait);
+ }
+
+ }
+ }
+}
+
+/*
+ * lib_ring_buffer_write_commit_counter
+ *
+ * For flight recording. must be called after commit.
+ * This function increments the subbuffer's commit_seq counter each time the
+ * commit count reaches back the reserve offset (modulo subbuffer size). It is
+ * useful for crash dump.
+ */
+static inline
+void lib_ring_buffer_write_commit_counter(const struct lib_ring_buffer_config *config,
+ struct lib_ring_buffer *buf,
+ struct channel *chan,
+ unsigned long idx,
+ unsigned long buf_offset,
+ unsigned long commit_count,
+ size_t slot_size)
+{
+ unsigned long offset, commit_seq_old;
+
+ if (config->oops != RING_BUFFER_OOPS_CONSISTENCY)
+ return;
+
+ offset = buf_offset + slot_size;
+
+ /*
+ * subbuf_offset includes commit_count_mask. We can simply
+ * compare the offsets within the subbuffer without caring about
+ * buffer full/empty mismatch because offset is never zero here
+ * (subbuffer header and record headers have non-zero length).
+ */
+ if (unlikely(subbuf_offset(offset - commit_count, chan)))
+ return;
+
+ commit_seq_old = v_read(config, &buf->commit_hot[idx].seq);
+ while ((long) (commit_seq_old - commit_count) < 0)
+ commit_seq_old = v_cmpxchg(config, &buf->commit_hot[idx].seq,
+ commit_seq_old, commit_count);
+}
+
+extern int lib_ring_buffer_create(struct lib_ring_buffer *buf,
+ struct channel_backend *chanb, int cpu);
+extern void lib_ring_buffer_free(struct lib_ring_buffer *buf);
+
+/* Keep track of trap nesting inside ring buffer code */
+DECLARE_PER_CPU(unsigned int, lib_ring_buffer_nesting);
+
+#endif /* _LINUX_RING_BUFFER_FRONTEND_INTERNAL_H */
projects / lttng-ust.git / blobdiff