update TODO

[lttng-ust.git] / libust / buffers.h

/*
 * buffers.h
 *
 * Copyright (C) 2009 - Pierre-Marc Fournier (pierre-marc dot fournier at polymtl dot ca)
 * Copyright (C) 2008 - Mathieu Desnoyers (mathieu.desnoyers@polymtl.ca)
 *
 */

#ifndef _UST_BUFFERS_H
#define _UST_BUFFERS_H

#include <kcompat/kref.h>
#include <assert.h>
#include "channels.h"
#include "tracerconst.h"
#include "tracercore.h"
#include "header-inline.h"
#include <usterr.h>

/***** SHOULD BE REMOVED ***** */

/*
 * BUFFER_TRUNC zeroes the subbuffer offset and the subbuffer number parts of
 * the offset, which leaves only the buffer number.
 */
#define BUFFER_TRUNC(offset, chan) \
        ((offset) & (~((chan)->alloc_size-1)))
#define BUFFER_OFFSET(offset, chan) ((offset) & ((chan)->alloc_size - 1))
#define SUBBUF_OFFSET(offset, chan) ((offset) & ((chan)->subbuf_size - 1))
#define SUBBUF_ALIGN(offset, chan) \
        (((offset) + (chan)->subbuf_size) & (~((chan)->subbuf_size - 1)))
#define SUBBUF_TRUNC(offset, chan) \
        ((offset) & (~((chan)->subbuf_size - 1)))
#define SUBBUF_INDEX(offset, chan) \
        (BUFFER_OFFSET((offset), chan) >> (chan)->subbuf_size_order)

/*
 * Tracks changes to rchan/rchan_buf structs
 */
#define UST_CHANNEL_VERSION             8

/**************************************/

struct commit_counters {
        local_t cc;
        local_t cc_sb;                  /* Incremented _once_ at sb switch */
};

struct ust_buffer {
        /* First 32 bytes cache-hot cacheline */
        local_t offset;                 /* Current offset in the buffer */
        struct commit_counters *commit_count;   /* Commit count per sub-buffer */
        atomic_long_t consumed;         /*
                                         * Current offset in the buffer
                                         * standard atomic access (shared)
                                         */
        unsigned long last_tsc;         /*
                                         * Last timestamp written in the buffer.
                                         */
        /* End of first 32 bytes cacheline */
        atomic_long_t active_readers;   /*
                                         * Active readers count
                                         * standard atomic access (shared)
                                         */
        local_t events_lost;
        local_t corrupted_subbuffers;
        /* one byte is written to this pipe when data is available, in order
           to wake the consumer */
        /* portability: Single byte writes must be as quick as possible. The kernel-side
           buffer must be large enough so the writer doesn't block. From the pipe(7)
           man page: Since linux 2.6.11, the pipe capacity is 65536 bytes. */
        int data_ready_fd_write;
        /* the reading end of the pipe */
        int data_ready_fd_read;

        unsigned int finalized;
//ust// struct timer_list switch_timer; /* timer for periodical switch */
        unsigned long switch_timer_interval; /* 0 = unset */

        struct ust_channel *chan;

        struct kref kref;
        void *buf_data;
        size_t buf_size;
        int shmid;
        unsigned int cpu;

        /* commit count per subbuffer; must be at end of struct */
        local_t commit_seq[0] ____cacheline_aligned;
} ____cacheline_aligned;

/*
 * A switch is done during tracing or as a final flush after tracing (so it
 * won't write in the new sub-buffer).
 * FIXME: make this message clearer
 */
enum force_switch_mode { FORCE_ACTIVE, FORCE_FLUSH };

extern int ltt_reserve_slot_lockless_slow(struct ust_trace *trace,
                struct ust_channel *ltt_channel, void **transport_data,
                size_t data_size, size_t *slot_size, long *buf_offset, u64 *tsc,
                unsigned int *rflags, int largest_align, int cpu);

extern void ltt_force_switch_lockless_slow(struct ust_buffer *buf,
                enum force_switch_mode mode);


static __inline__ void ust_buffers_do_copy(void *dest, const void *src, size_t len)
{
        union {
                const void *src;
                const u8 *src8;
                const u16 *src16;
                const u32 *src32;
                const u64 *src64;
        } u = { .src = src };

        switch (len) {
        case 0: break;
        case 1: *(u8 *)dest = *u.src8;
                break;
        case 2: *(u16 *)dest = *u.src16;
                break;
        case 4: *(u32 *)dest = *u.src32;
                break;
        case 8: *(u64 *)dest = *u.src64;
                break;
        default:
                memcpy(dest, src, len);
        }
}

static __inline__ void *ust_buffers_offset_address(struct ust_buffer *buf, size_t offset)
{
        return ((char *)buf->buf_data)+offset;
}

/*
 * Last TSC comparison functions. Check if the current TSC overflows
 * LTT_TSC_BITS bits from the last TSC read. Reads and writes last_tsc
 * atomically.
 */

/* FIXME: does this test work properly? */
#if (BITS_PER_LONG == 32)
static __inline__ void save_last_tsc(struct ust_buffer *ltt_buf,
                                        u64 tsc)
{
        ltt_buf->last_tsc = (unsigned long)(tsc >> LTT_TSC_BITS);
}

static __inline__ int last_tsc_overflow(struct ust_buffer *ltt_buf,
                                        u64 tsc)
{
        unsigned long tsc_shifted = (unsigned long)(tsc >> LTT_TSC_BITS);

        if (unlikely((tsc_shifted - ltt_buf->last_tsc)))
                return 1;
        else
                return 0;
}
#else
static __inline__ void save_last_tsc(struct ust_buffer *ltt_buf,
                                        u64 tsc)
{
        ltt_buf->last_tsc = (unsigned long)tsc;
}

static __inline__ int last_tsc_overflow(struct ust_buffer *ltt_buf,
                                        u64 tsc)
{
        if (unlikely((tsc - ltt_buf->last_tsc) >> LTT_TSC_BITS))
                return 1;
        else
                return 0;
}
#endif

static __inline__ void ltt_reserve_push_reader(
                struct ust_channel *rchan,
                struct ust_buffer *buf,
                long offset)
{
        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 the buffer is not in overwrite mode, pushing the reader
                 * only happens if a sub-buffer is corrupted.
                 */
                if (unlikely((SUBBUF_TRUNC(offset, buf->chan)
                   - SUBBUF_TRUNC(consumed_old, buf->chan))
                   >= rchan->alloc_size))
                        consumed_new = SUBBUF_ALIGN(consumed_old, buf->chan);
                else
                        return;
        } while (unlikely(atomic_long_cmpxchg(&buf->consumed, consumed_old,
                        consumed_new) != consumed_old));
}

static __inline__ void ltt_vmcore_check_deliver(
                struct ust_buffer *buf,
                long commit_count, long idx)
{
        local_set(&buf->commit_seq[idx], commit_count);
}

static __inline__ void ltt_check_deliver(struct ust_channel *chan,
                struct ust_buffer *buf,
                long offset, long commit_count, long idx)
{
        long old_commit_count = commit_count - chan->subbuf_size;

        /* Check if all commits have been done */
        if (unlikely((BUFFER_TRUNC(offset, chan)
                        >> chan->n_subbufs_order)
                        - (old_commit_count
                           & chan->commit_count_mask) == 0)) {
                /*
                 * If we succeeded in updating the cc_sb, we are delivering
                 * the subbuffer. Deals with concurrent updates of the "cc"
                 * value without adding a add_return atomic operation to the
                 * fast path.
                 */
                if (likely(local_cmpxchg(&buf->commit_count[idx].cc_sb,
                                         old_commit_count, commit_count)
                           == old_commit_count)) {
                        int result;

                        /*
                         * Set noref flag for this subbuffer.
                         */
//ust//                 ltt_set_noref_flag(rchan, buf, idx);
                        ltt_vmcore_check_deliver(buf, commit_count, idx);

                        /* wakeup consumer */
                        result = write(buf->data_ready_fd_write, "1", 1);
                        if(result == -1) {
                                PERROR("write (in ltt_relay_buffer_flush)");
                                ERR("this should never happen!");
                        }
                }
        }
}

static __inline__ int ltt_poll_deliver(struct ust_channel *chan, struct ust_buffer *buf)
{
        long consumed_old, consumed_idx, commit_count, write_offset;

        consumed_old = atomic_long_read(&buf->consumed);
        consumed_idx = SUBBUF_INDEX(consumed_old, buf->chan);
        commit_count = local_read(&buf->commit_count[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 = local_read(&buf->offset);

        /*
         * Check that the subbuffer we are trying to consume has been
         * already fully committed.
         */

        if (((commit_count - chan->subbuf_size)
             & chan->commit_count_mask)
            - (BUFFER_TRUNC(consumed_old, buf->chan)
               >> chan->n_subbufs_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, buf->chan)
           - SUBBUF_TRUNC(consumed_old, buf->chan))
           == 0)
                return 0;

        return 1;

}

/*
 * returns 0 if reserve ok, or 1 if the slow path must be taken.
 */
static __inline__ int ltt_relay_try_reserve(
                struct ust_channel *chan,
                struct ust_buffer *buf,
                size_t data_size,
                u64 *tsc, unsigned int *rflags, int largest_align,
                long *o_begin, long *o_end, long *o_old,
                size_t *before_hdr_pad, size_t *size)
{
        *o_begin = local_read(&buf->offset);
        *o_old = *o_begin;

        *tsc = trace_clock_read64();

//ust// #ifdef CONFIG_LTT_VMCORE
//ust//         prefetch(&buf->commit_count[SUBBUF_INDEX(*o_begin, rchan)]);
//ust//         prefetch(&buf->commit_seq[SUBBUF_INDEX(*o_begin, rchan)]);
//ust// #else
//ust//         prefetchw(&buf->commit_count[SUBBUF_INDEX(*o_begin, rchan)]);
//ust// #endif
        if (last_tsc_overflow(buf, *tsc))
                *rflags = LTT_RFLAG_ID_SIZE_TSC;

        if (unlikely(SUBBUF_OFFSET(*o_begin, buf->chan) == 0))
                return 1;

        *size = ust_get_header_size(chan,
                                *o_begin, data_size,
                                before_hdr_pad, *rflags);
        *size += ltt_align(*o_begin + *size, largest_align) + data_size;
        if (unlikely((SUBBUF_OFFSET(*o_begin, buf->chan) + *size)
                     > buf->chan->subbuf_size))
                return 1;

        /*
         * Event fits in the current buffer and we are not on a switch
         * boundary. It's safe to write.
         */
        *o_end = *o_begin + *size;

        if (unlikely((SUBBUF_OFFSET(*o_end, buf->chan)) == 0))
                /*
                 * The offset_end will fall at the very beginning of the next
                 * subbuffer.
                 */
                return 1;

        return 0;
}

static __inline__ int ltt_reserve_slot(struct ust_trace *trace,
                struct ust_channel *chan, void **transport_data,
                size_t data_size, size_t *slot_size, long *buf_offset, u64 *tsc,
                unsigned int *rflags, int largest_align, int cpu)
{
        struct ust_buffer *buf = chan->buf[cpu];
        long o_begin, o_end, o_old;
        size_t before_hdr_pad;

        /*
         * Perform retryable operations.
         */
        /* FIXME: make this rellay per cpu? */
        if (unlikely(LOAD_SHARED(ltt_nesting) > 4)) {
                DBG("Dropping event because nesting is too deep.");
                local_inc(&buf->events_lost);
                return -EPERM;
        }

        if (unlikely(ltt_relay_try_reserve(chan, buf,
                        data_size, tsc, rflags,
                        largest_align, &o_begin, &o_end, &o_old,
                        &before_hdr_pad, slot_size)))
                goto slow_path;

        if (unlikely(local_cmpxchg(&buf->offset, o_old, o_end) != o_old))
                goto slow_path;

        /*
         * Atomically update last_tsc. This update races against concurrent
         * atomic updates, but the race will always cause supplementary full TSC
         * events, never the opposite (missing a full TSC event when it would be
         * needed).
         */
        save_last_tsc(buf, *tsc);

        /*
         * Push the reader if necessary
         */
        ltt_reserve_push_reader(chan, buf, o_end - 1);

        /*
         * Clear noref flag for this subbuffer.
         */
//ust// ltt_clear_noref_flag(chan, buf, SUBBUF_INDEX(o_end - 1, chan));

        *buf_offset = o_begin + before_hdr_pad;
        return 0;
slow_path:
        return ltt_reserve_slot_lockless_slow(trace, chan,
                transport_data, data_size, slot_size, buf_offset, tsc,
                rflags, largest_align, cpu);
}

/*
 * Force a sub-buffer switch for a per-cpu buffer. This operation is
 * completely reentrant : can be called while tracing is active with
 * absolutely no lock held.
 *
 * Note, however, that as a local_cmpxchg is used for some atomic
 * operations, this function must be called from the CPU which owns the buffer
 * for a ACTIVE flush.
 */
static __inline__ void ltt_force_switch(struct ust_buffer *buf,
                enum force_switch_mode mode)
{
        return ltt_force_switch_lockless_slow(buf, mode);
}

/*
 * for flight recording. must be called after relay_commit.
 * This function increments the subbuffers's commit_seq counter each time the
 * commit count reaches back the reserve offset (module subbuffer size). It is
 * useful for crash dump.
 */
//ust// #ifdef CONFIG_LTT_VMCORE
static __inline__ void ltt_write_commit_counter(struct ust_channel *chan,
                struct ust_buffer *buf, long idx, long buf_offset,
                long commit_count, size_t data_size)
{
        long offset;
        long commit_seq_old;

        offset = buf_offset + data_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 event headers have non-zero length).
         */
        if (unlikely(SUBBUF_OFFSET(offset - commit_count, buf->chan)))
                return;

        commit_seq_old = local_read(&buf->commit_seq[idx]);
        while (commit_seq_old < commit_count)
                commit_seq_old = local_cmpxchg(&buf->commit_seq[idx],
                                         commit_seq_old, commit_count);

        DBG("commit_seq for channel %s_%d, subbuf %ld is now %ld", buf->chan->channel_name, buf->cpu, idx, commit_count);
}
//ust// #else
//ust// static __inline__ void ltt_write_commit_counter(struct ust_buffer *buf,
//ust//                 long idx, long buf_offset, long commit_count, size_t data_size)
//ust// {
//ust// }
//ust// #endif

/*
 * Atomic unordered slot commit. Increments the commit count in the
 * specified sub-buffer, and delivers it if necessary.
 *
 * Parameters:
 *
 * @ltt_channel : channel structure
 * @transport_data: transport-specific data
 * @buf_offset : offset following the event header.
 * @data_size : size of the event data.
 * @slot_size : size of the reserved slot.
 */
static __inline__ void ltt_commit_slot(
                struct ust_channel *chan,
                struct ust_buffer *buf, long buf_offset,
                size_t data_size, size_t slot_size)
{
        long offset_end = buf_offset;
        long endidx = SUBBUF_INDEX(offset_end - 1, chan);
        long commit_count;

#ifdef LTT_NO_IPI_BARRIER
        smp_wmb();
#else
        /*
         * Must write slot data before incrementing commit count.
         * This compiler barrier is upgraded into a smp_mb() by the IPI
         * sent by get_subbuf().
         */
        barrier();
#endif
        local_add(slot_size, &buf->commit_count[endidx].cc);
        /*
         * commit count read can race with concurrent OOO commit count updates.
         * This is only needed for ltt_check_deliver (for non-polling delivery
         * only) and for ltt_write_commit_counter. The race can only cause the
         * counter to be read with the same value more than once, which could
         * cause :
         * - Multiple delivery for the same sub-buffer (which is handled
         *   gracefully by the reader code) if the value is for a full
         *   sub-buffer. It's important that we can never miss a sub-buffer
         *   delivery. Re-reading the value after the local_add ensures this.
         * - Reading a commit_count with a higher value that what was actually
         *   added to it for the ltt_write_commit_counter call (again caused by
         *   a concurrent committer). It does not matter, because this function
         *   is interested in the fact that the commit count reaches back the
         *   reserve offset for a specific sub-buffer, which is completely
         *   independent of the order.
         */
        commit_count = local_read(&buf->commit_count[endidx].cc);

        ltt_check_deliver(chan, buf, offset_end - 1, commit_count, endidx);
        /*
         * Update data_size for each commit. It's needed only for extracting
         * ltt buffers from vmcore, after crash.
         */
        ltt_write_commit_counter(chan, buf, endidx, buf_offset, commit_count, data_size);
}

void _ust_buffers_write(struct ust_buffer *buf, size_t offset,
        const void *src, size_t len, ssize_t cpy);

static __inline__ int ust_buffers_write(struct ust_buffer *buf, size_t offset,
        const void *src, size_t len)
{
        size_t cpy;
        size_t buf_offset = BUFFER_OFFSET(offset, buf->chan);

        assert(buf_offset < buf->chan->subbuf_size*buf->chan->subbuf_cnt);

        cpy = min_t(size_t, len, buf->buf_size - buf_offset);
        ust_buffers_do_copy(buf->buf_data + buf_offset, src, cpy);

        if (unlikely(len != cpy))
                _ust_buffers_write(buf, buf_offset, src, len, cpy);
        return len;
}

int ust_buffers_get_subbuf(struct ust_buffer *buf, long *consumed);
int ust_buffers_put_subbuf(struct ust_buffer *buf, unsigned long uconsumed_old);

#endif /* _UST_BUFFERS_H */