X-Git-Url: http://git.lttng.org./?a=blobdiff_plain;f=usertrace-fast%2Fltt-usertrace-fast.c;h=fc919c348452d8a52dffcdadea560daa7c462d2a;hb=5ffa9d14c030ab0ac4724950721f9b0c24974254;hp=3d64e781efbbe556ca730f06ec0a3bd84866b7bf;hpb=77b31f39f7febe0a1cdd4c1297b73918e5efaca0;p=lttv.git diff --git a/usertrace-fast/ltt-usertrace-fast.c b/usertrace-fast/ltt-usertrace-fast.c index 3d64e781..fc919c34 100644 --- a/usertrace-fast/ltt-usertrace-fast.c +++ b/usertrace-fast/ltt-usertrace-fast.c @@ -41,6 +41,7 @@ * */ +#define _GNU_SOURCE #include #include #include @@ -58,11 +59,14 @@ #include #include #include +#include +#include #include //for get_cycles() #include "ltt-usertrace-fast.h" +enum force_switch_mode { FORCE_ACTIVE, FORCE_FLUSH }; /* Writer (the traced application) */ @@ -116,6 +120,248 @@ static void handler_sigalarm(int signo) alarm(3); } +/* Do a buffer switch. Don't switch if buffer is completely empty */ +static void flush_buffer(struct ltt_buf *ltt_buf, enum force_switch_mode mode) +{ + uint64_t tsc; + int offset_begin, offset_end, offset_old; + int reserve_commit_diff; + int consumed_old, consumed_new; + int commit_count, reserve_count; + int end_switch_old; + + do { + offset_old = atomic_read(<t_buf->offset); + offset_begin = offset_old; + end_switch_old = 0; + tsc = ltt_get_timestamp(); + if(tsc == 0) { + /* Error in getting the timestamp : should not happen : it would + * mean we are called from an NMI during a write seqlock on xtime. */ + return; + } + + if(SUBBUF_OFFSET(offset_begin, ltt_buf) != 0) { + offset_begin = SUBBUF_ALIGN(offset_begin, ltt_buf); + end_switch_old = 1; + } else { + /* we do not have to switch : buffer is empty */ + return; + } + if(mode == FORCE_ACTIVE) + offset_begin += ltt_subbuf_header_len(ltt_buf); + /* Always begin_switch in FORCE_ACTIVE mode */ + + /* Test new buffer integrity */ + reserve_commit_diff = + atomic_read( + <t_buf->reserve_count[SUBBUF_INDEX(offset_begin, ltt_buf)]) + - atomic_read( + <t_buf->commit_count[SUBBUF_INDEX(offset_begin, ltt_buf)]); + if(reserve_commit_diff == 0) { + /* Next buffer not corrupted. */ + if(mode == FORCE_ACTIVE + && (offset_begin-atomic_read(<t_buf->consumed)) + >= ltt_buf->alloc_size) { + /* We do not overwrite non consumed buffers and we are full : ignore + switch while tracing is active. */ + return; + } + } else { + /* Next subbuffer corrupted. Force pushing reader even in normal mode */ + } + + offset_end = offset_begin; + } while(atomic_cmpxchg(<t_buf->offset, offset_old, offset_end) + != offset_old); + + + if(mode == FORCE_ACTIVE) { + /* Push the reader if necessary */ + do { + consumed_old = atomic_read(<t_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 fartest 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 + happen if a sub-buffer is corrupted */ + if((SUBBUF_TRUNC(offset_end, ltt_buf) + - SUBBUF_TRUNC(consumed_old, ltt_buf)) + >= ltt_buf->alloc_size) + consumed_new = SUBBUF_ALIGN(consumed_old, ltt_buf); + else { + consumed_new = consumed_old; + break; + } + } while(atomic_cmpxchg(<t_buf->consumed, consumed_old, consumed_new) + != consumed_old); + + if(consumed_old != consumed_new) { + /* Reader pushed : we are the winner of the push, we can therefore + reequilibrate reserve and commit. Atomic increment of the commit + count permits other writers to play around with this variable + before us. We keep track of corrupted_subbuffers even in overwrite + mode : + we never want to write over a non completely committed sub-buffer : + possible causes : the buffer size is too low compared to the unordered + data input, or there is a writer who died between the reserve and the + commit. */ + if(reserve_commit_diff) { + /* We have to alter the sub-buffer commit count : a sub-buffer is + corrupted */ + atomic_add(reserve_commit_diff, + <t_buf->commit_count[SUBBUF_INDEX(offset_begin, ltt_buf)]); + atomic_inc(<t_buf->corrupted_subbuffers); + } + } + } + + /* Always switch */ + + if(end_switch_old) { + /* old subbuffer */ + /* Concurrency safe because we are the last and only thread to alter this + sub-buffer. As long as it is not delivered and read, no other thread can + alter the offset, alter the reserve_count or call the + client_buffer_end_callback on this sub-buffer. + The only remaining threads could be the ones with pending commits. They + will have to do the deliver themself. + Not concurrency safe in overwrite mode. We detect corrupted subbuffers with + commit and reserve counts. We keep a corrupted sub-buffers count and push + the readers across these sub-buffers. + Not concurrency safe if a writer is stalled in a subbuffer and + another writer switches in, finding out it's corrupted. The result will be + than the old (uncommited) subbuffer will be declared corrupted, and that + the new subbuffer will be declared corrupted too because of the commit + count adjustment. + Offset old should never be 0. */ + ltt_buffer_end_callback(ltt_buf, tsc, offset_old, + SUBBUF_INDEX((offset_old), ltt_buf)); + /* Setting this reserve_count will allow the sub-buffer to be delivered by + the last committer. */ + reserve_count = atomic_add_return((SUBBUF_OFFSET((offset_old-1), + ltt_buf) + 1), + <t_buf->reserve_count[SUBBUF_INDEX((offset_old), + ltt_buf)]); + if(reserve_count == atomic_read( + <t_buf->commit_count[SUBBUF_INDEX((offset_old), ltt_buf)])) { + ltt_deliver_callback(ltt_buf, SUBBUF_INDEX((offset_old), ltt_buf), NULL); + } + } + + if(mode == FORCE_ACTIVE) { + /* New sub-buffer */ + /* This code can be executed unordered : writers may already have written + to the sub-buffer before this code gets executed, caution. */ + /* The commit makes sure that this code is executed before the deliver + of this sub-buffer */ + ltt_buffer_begin_callback(ltt_buf, tsc, SUBBUF_INDEX(offset_begin, ltt_buf)); + commit_count = atomic_add_return(ltt_subbuf_header_len(ltt_buf), + <t_buf->commit_count[SUBBUF_INDEX(offset_begin, ltt_buf)]); + /* Check if the written buffer has to be delivered */ + if(commit_count == atomic_read( + <t_buf->reserve_count[SUBBUF_INDEX(offset_begin, ltt_buf)])) { + ltt_deliver_callback(ltt_buf, SUBBUF_INDEX(offset_begin, ltt_buf), NULL); + } + } + +} + +static inline int ltt_buffer_get(struct ltt_buf *ltt_buf, + unsigned int *offset) +{ + unsigned int consumed_old, consumed_idx; + consumed_old = atomic_read(<t_buf->consumed); + consumed_idx = SUBBUF_INDEX(consumed_old, ltt_buf); + + if(atomic_read(<t_buf->commit_count[consumed_idx]) + != atomic_read(<t_buf->reserve_count[consumed_idx])) { + return -EAGAIN; + } + if((SUBBUF_TRUNC(atomic_read(<t_buf->offset), ltt_buf) + -SUBBUF_TRUNC(consumed_old, ltt_buf)) == 0) { + return -EAGAIN; + } + + *offset = consumed_old; + + return 0; +} + +static inline int ltt_buffer_put(struct ltt_buf *ltt_buf, + unsigned int offset) +{ + unsigned int consumed_old, consumed_new; + int ret; + + consumed_old = offset; + consumed_new = SUBBUF_ALIGN(consumed_old, ltt_buf); + if(atomic_cmpxchg(<t_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. */ + return -EIO; + } else { + if(atomic_read(<t_buf->full) == 1) { + /* tell the client that buffer is now unfull */ + ret = futex((unsigned long)<t_buf->full, + FUTEX_WAKE, 1, 0, 0, 0); + if(ret != 1) { + printf("LTT warning : race condition : writer not waiting or too many writers\n"); + } + atomic_set(<t_buf->full, 0); + } + } +} + +static int read_subbuffer(struct ltt_buf *ltt_buf, int fd) +{ + unsigned int consumed_old; + int err; + printf("LTT read buffer\n"); + + + err = ltt_buffer_get(ltt_buf, &consumed_old); + if(err != 0) { + if(err != -EAGAIN) printf("LTT Reserving sub buffer failed\n"); + goto get_error; + } + + err = TEMP_FAILURE_RETRY(write(fd, + ltt_buf->start + + (consumed_old & ((ltt_buf->alloc_size)-1)), + ltt_buf->subbuf_size)); + + if(err < 0) { + perror("Error in writing to file"); + goto write_error; + } +#if 0 + err = fsync(pair->trace); + if(err < 0) { + ret = errno; + perror("Error in writing to file"); + goto write_error; + } +#endif //0 +write_error: + err = ltt_buffer_put(ltt_buf, consumed_old); + + if(err != 0) { + if(err == -EIO) { + printf("Reader has been pushed by the writer, last subbuffer corrupted.\n"); + /* FIXME : we may delete the last written buffer if we wish. */ + } + goto get_error; + } + +get_error: + return err; +} /* This function is called by ltt_rw_init which has signals blocked */ static void ltt_usertrace_fast_daemon(struct ltt_trace_info *shared_trace_info, @@ -176,10 +422,10 @@ static void ltt_usertrace_fast_daemon(struct ltt_trace_info *shared_trace_info, snprintf(identifier_name, PATH_MAX-1, "%lu.%lu.%llu", traced_pid, traced_thread, get_cycles()); snprintf(outfile_name, PATH_MAX-1, "facilities-%s", identifier_name); - fd_fac = creat(outfile_name, 0666); + fd_fac = creat(outfile_name, 0644); snprintf(outfile_name, PATH_MAX-1, "cpu-%s", identifier_name); - fd_cpu = creat(outfile_name, 0666); + fd_cpu = creat(outfile_name, 0644); while(1) { @@ -187,16 +433,34 @@ static void ltt_usertrace_fast_daemon(struct ltt_trace_info *shared_trace_info, if(traced_pid == 0) break; /* parent died */ if(parent_exited) break; printf("LTT Doing a buffer switch read. pid is : %lu\n", getpid()); - //printf("Test parent. pid is : %lu, ppid is %lu\n", getpid(), getppid()); + + do { + ret = read_subbuffer(&shared_trace_info->channel.cpu, fd_cpu); + } while(ret == 0); + + do { + ret = read_subbuffer(&shared_trace_info->channel.facilities, fd_fac); + } while(ret == 0); } - /* Buffer force switch (flush) */ - //TODO - + /* The parent thread is dead and we have finished with the buffer */ + + /* Buffer force switch (flush). Using FLUSH instead of ACTIVE because we know + * there is no writer. */ + flush_buffer(&shared_trace_info->channel.cpu, FORCE_FLUSH); + do { + ret = read_subbuffer(&shared_trace_info->channel.cpu, fd_cpu); + } while(ret == 0); + + + flush_buffer(&shared_trace_info->channel.facilities, FORCE_FLUSH); + do { + ret = read_subbuffer(&shared_trace_info->channel.facilities, fd_fac); + } while(ret == 0); + close(fd_fac); close(fd_cpu); - /* The parent thread is dead and we have finished with the buffer */ munmap(shared_trace_info, sizeof(*shared_trace_info)); exit(0); @@ -222,6 +486,23 @@ void ltt_rw_init(void) shared_trace_info = mmap(0, sizeof(*thread_trace_info), PROT_READ|PROT_WRITE, MAP_SHARED|MAP_ANONYMOUS, 0, 0); memset(shared_trace_info, 0, sizeof(*shared_trace_info)); + /* Tricky semaphore : is in a shared memory space, so it's ok for a fast + * mutex (futex). */ + atomic_set(&shared_trace_info->channel.facilities.full, 0); + shared_trace_info->channel.facilities.alloc_size = LTT_BUF_SIZE_FACILITIES; + shared_trace_info->channel.facilities.subbuf_size = LTT_SUBBUF_SIZE_FACILITIES; + shared_trace_info->channel.facilities.start = + shared_trace_info->channel.facilities_buf; + ltt_buffer_begin_callback(&shared_trace_info->channel.facilities, + ltt_get_timestamp(), 0); + + atomic_set(&shared_trace_info->channel.cpu.full, 0); + shared_trace_info->channel.cpu.alloc_size = LTT_BUF_SIZE_CPU; + shared_trace_info->channel.cpu.subbuf_size = LTT_SUBBUF_SIZE_CPU; + shared_trace_info->channel.cpu.start = shared_trace_info->channel.cpu_buf; + ltt_buffer_begin_callback(&shared_trace_info->channel.cpu, + ltt_get_timestamp(), 0); + shared_trace_info->init = 1; /* Disable signals */