X-Git-Url: http://git.lttng.org/?a=blobdiff_plain;f=trunk%2Fverif%2Fnico%2Fmodels%2Fmodel_02.spin;fp=trunk%2Fverif%2Fnico%2Fmodels%2Fmodel_02.spin;h=671e9f2ef4e32cced6c6eecbedb76bf75b84fb0e;hb=dc45444e22c8e7fc3296f00924e4472257f96d79;hp=0000000000000000000000000000000000000000;hpb=1db0bd6a4b0334ca18e21d3c9c27476696a33e15;p=lttv.git diff --git a/trunk/verif/nico/models/model_02.spin b/trunk/verif/nico/models/model_02.spin new file mode 100755 index 00000000..671e9f2e --- /dev/null +++ b/trunk/verif/nico/models/model_02.spin @@ -0,0 +1,298 @@ +/* LTTng ltt-tracer.c atomic lockless buffering scheme Promela model v2 + * Created for the Spin validator. + * Mathieu Desnoyers + * October 2008 + + * TODO : create test cases that will generate an overflow on the offset and + * counter type. Counter types smaller than a byte should be used. + + * Promela only has unsigned char, no signed char. + * Because detection of difference < 0 depends on a signed type, but we want + * compactness, check also for the values being higher than half of the unsigned + * char range (and consider them negative). The model, by design, does not use + * offsets or counts higher than 127 because we would then have to use a larger + * type (short or int). + */ +#define HALF_UCHAR (255/2) + +/* NUMPROCS 4 : causes event loss with some reader timings. + * e.g. 3 events, 1 switch, 1 event (lost, buffer full), read 1 subbuffer + */ +#define NUMPROCS 4 + +/* NUMPROCS 3 : does not cause event loss because buffers are big enough. + * #define NUMPROCS 3 + * e.g. 3 events, 1 switch, read 1 subbuffer + */ + +#define NUMSWITCH 1 +#define BUFSIZE 4 +#define NR_SUBBUFS 2 +#define SUBBUF_SIZE (BUFSIZE / NR_SUBBUFS) + +/* Writer counters +*/ +byte write_off = 0; +byte commit_count[NR_SUBBUFS]; + +/* Reader counters +*/ +byte read_off = 0; + +byte events_lost = 0; +byte refcount = 0; + +bool deliver = 0; + +/* buffer slot in-use bit. Detects racy use (more than a single process + * accessing a slot at any given step). + */ +bool buffer_use[BUFSIZE]; + +/* Proceed to a sub-subber switch is needed. + * Used in a periodical timer interrupt to fill and ship the current subbuffer + * to the reader so we can guarantee a steady flow. If a subbuffer is + * completely empty, do not switch. + * Also used as "finalize" operation to complete the last subbuffer after + * all writers have finished so the last subbuffer can be read by the reader. + */ +proctype switcher() +{ + byte prev_off, new_off, tmp_commit; + byte size; + +cmpxchg_loop: + atomic { + prev_off = write_off; + size = SUBBUF_SIZE - (prev_off % SUBBUF_SIE); + new_off = prev_off + size; + if + :: (new_off - read_off > BUFSIZE && new_off - read_off < HALF_UCHAR) + || size == SUBBUF_SIZE -> + refcount = refcount - 1; + goto not_needed; + :: else -> skip + fi; + } + atomic { + if + :: prev_off != write_off -> goto cmpxchg_loop + :: else -> write_off = new_off; + fi; + } + + atomic { + tmp_commit = commit_count[(prev_off % BUFSIZE) / SUBBUF_SIZE] + size; + commit_count[(prev_off % BUFSIZE) / SUBBUF_SIZE] = tmp_commit; + if + :: (((prev_off / BUFSIZE) * BUFSIZE) / NR_SUBBUFS) + SUBBUF_SIZE - + tmp_commit + -> deliver = 1 + :: else + -> skip + fi; + refcount = refcount - 1; + } +not_needed: + skip; +} + +/* tracer + * Writes 1 byte of information in the buffer at the current + * "write_off" position and then increment the commit_count of the sub-buffer + * the information has been written to. + */ +proctype tracer() +{ + byte size = 1; + byte prev_off, new_off, tmp_commit; + byte i, j; + +cmpxchg_loop: + atomic { + prev_off = write_off; + new_off = prev_off + size; + } + atomic { + if + :: new_off - read_off > BUFSIZE && new_off - read_off < HALF_UCHAR -> + goto lost + :: else -> skip + fi; + } + atomic { + if + :: prev_off != write_off -> goto cmpxchg_loop + :: else -> write_off = new_off; + fi; + i = 0; + do + :: i < size -> + assert(buffer_use[(prev_off + i) % BUFSIZE] == 0); + buffer_use[(prev_off + i) % BUFSIZE] = 1; + i++ + :: i >= size -> break + od; + } + + /* writing to buffer... + */ + + atomic { + i = 0; + do + :: i < size -> + buffer_use[(prev_off + i) % BUFSIZE] = 0; + i++ + :: i >= size -> break + od; + tmp_commit = commit_count[(prev_off % BUFSIZE) / SUBBUF_SIZE] + size; + commit_count[(prev_off % BUFSIZE) / SUBBUF_SIZE] = tmp_commit; + if + :: (((prev_off / BUFSIZE) * BUFSIZE) / NR_SUBBUFS) + SUBBUF_SIZE - + tmp_commit + -> deliver = 1 + :: else + -> skip + fi; + } + atomic { + goto end; +lost: + events_lost++; +end: + refcount = refcount - 1; + } +} + +/* reader + * Read the information sub-buffer per sub-buffer when available. + * + * Reads the information as soon as it is ready, or may be delayed by + * an asynchronous delivery. Being modeled as a process insures all cases + * (scheduled very quickly or very late, causing event loss) are covered. + * Only one reader per buffer (normally ensured by a mutex). This is modeled + * by using a single reader process. + */ +proctype reader() +{ + byte i, j; + + do + :: (write_off / SUBBUF_SIZE) - (read_off / SUBBUF_SIZE) > 0 + && (write_off / SUBBUF_SIZE) - (read_off / SUBBUF_SIZE) < HALF_UCHAR + && (commit_count[(read_off % BUFSIZE) / SUBBUF_SIZE] + - SUBBUF_SIZE - (((read_off / BUFSIZE) * BUFSIZE) / NR_SUBBUFS) + == 0) -> + atomic { + i = 0; + do + :: i < SUBBUF_SIZE -> + assert(buffer_use[(read_off + i) % BUFSIZE] == 0); + buffer_use[(read_off + i) % BUFSIZE] = 1; + i++ + :: i >= SUBBUF_SIZE -> break + od; + } + + /* reading from buffer... + */ + + atomic { + i = 0; + do + :: i < SUBBUF_SIZE -> + buffer_use[(read_off + i) % BUFSIZE] = 0; + i++ + :: i >= SUBBUF_SIZE -> break + od; + read_off = read_off + SUBBUF_SIZE; + } + :: read_off >= (NUMPROCS - events_lost) -> break; + od; +} + +/* Waits for all tracer and switcher processes to finish before finalizing + * the buffer. Only after that will the reader be allowed to read the + * last subbuffer. + */ +proctype cleaner() +{ + atomic { + do + :: refcount == 0 -> + refcount = refcount + 1; + run switcher(); /* Finalize the last sub-buffer so it can be read. */ + break; + od; + } +} + +init { + byte i = 0; + byte j = 0; + byte sum = 0; + byte commit_sum = 0; + + atomic { + i = 0; + do + :: i < NR_SUBBUFS -> + commit_count[i] = 0; + i++ + :: i >= NR_SUBBUFS -> break + od; + i = 0; + do + :: i < BUFSIZE -> + buffer_use[i] = 0; + i++ + :: i >= BUFSIZE -> break + od; + run reader(); + run cleaner(); + i = 0; + do + :: i < NUMPROCS -> + refcount = refcount + 1; + run tracer(); + i++ + :: i >= NUMPROCS -> break + od; + i = 0; + do + :: i < NUMSWITCH -> + refcount = refcount + 1; + run switcher(); + i++ + :: i >= NUMSWITCH -> break + od; + } + + /* Assertions. + */ + atomic { + /* The writer head must always be superior or equal to the reader head. + */ + /*assert(write_off - read_off >= 0 && write_off - read_off < HALF_UCHAR);*/ + j = 0; + commit_sum = 0; + do + :: j < NR_SUBBUFS -> + commit_sum = commit_sum + commit_count[j]; + j++ + :: j >= NR_SUBBUFS -> break + od; + /* The sum of all subbuffer commit counts must always be lower or equal + * to the writer head, because space must be reserved before it is + * written to and then committed. + */ + assert(write_off - commit_sum >= 0 && write_off - commit_sum < HALF_UCHAR); + + /* If we have less writers than the buffer space available, we should + * not loose events + */ + assert(NUMPROCS + NUMSWITCH > BUFSIZE || events_lost == 0); + } +} +