There are two approaches to read compressed trace data:
- use a temporary file to decompress entire trace data before reading
- use in-memory decompression of requested trace data chunk only
In-memory decompression seems to be more efficient, but selecting which
approach to use depends in the use case.
A compression chunk consists of multiple trace pages, that's why a small
cache with uncompressed chunks is implemented. The chunk stays in the
cache until there are pages which have reference to it.
Signed-off-by: Tzvetomir Stoyanov (VMware) <tz.stoyanov@xxxxxxxxx>
---
lib/trace-cmd/trace-input.c | 110 ++++++++++++++++++++++++++++++++++++
1 file changed, 110 insertions(+)
diff --git a/lib/trace-cmd/trace-input.c b/lib/trace-cmd/trace-input.c
index 0fd1a451..040fb391 100644
--- a/lib/trace-cmd/trace-input.c
+++ b/lib/trace-cmd/trace-input.c
@@ -29,6 +29,9 @@
#define COMMIT_MASK ((1 << 27) - 1)
+/* force uncompressing in memory */
+#define INMEMORY_DECOMPRESS
+
/* for debugging read instead of mmap */
static int force_read = 0;
@@ -1257,6 +1260,105 @@ static void free_page_map(struct page_map *page_map)
free(page_map);
}
+#define CHUNK_CHECK_OFFSET(C, O) ((O) >= (C)->offset && (O) < ((C)->offset + (C)->size))
+static struct tracecmd_compress_chunk *get_zchunk(struct cpu_data *cpu, off64_t offset)
+{
+ struct cpu_zdata *cpuz = &cpu->compress;
+ int min, mid, max;
+
+ if (!cpuz->chunks)
+ return NULL;
+ if (offset > (cpuz->chunks[cpuz->count - 1].offset + cpuz->chunks[cpuz->count - 1].size))
+ return NULL;
+
+ /* check if the requested offset is in the last requested chunk or in the next chunk */
+ if (CHUNK_CHECK_OFFSET(cpuz->chunks + cpuz->last_chunk, offset))
+ return cpuz->chunks + cpuz->last_chunk;
+ cpuz->last_chunk++;
+ if (cpuz->last_chunk < cpuz->count &&
+ CHUNK_CHECK_OFFSET(cpuz->chunks + cpuz->last_chunk, offset))
+ return cpuz->chunks + cpuz->last_chunk;
+
+ /* do a binary search to find the chunk holding the given offset */
+ min = 0;
+ max = cpuz->count - 1;
+ mid = (min + max)/2;
+ while (min <= max) {
+ if (offset < cpuz->chunks[mid].offset)
+ max = mid - 1;
+ else if (offset > (cpuz->chunks[mid].offset + cpuz->chunks[mid].size))
+ min = mid + 1;
+ else
+ break;
+ mid = (min + max)/2;
+ }
+ cpuz->last_chunk = mid;
+ return cpuz->chunks + mid;
+}
+
+static void free_zpage(struct cpu_data *cpu_data, void *map)
+{
+ struct zchunk_cache *cache;
+
+ list_for_each_entry(cache, &cpu_data->compress.cache, list) {
+ if (map <= cache->map && map > (cache->map + cache->chunk->size))
+ goto found;
+ }
+ return;
+
+found:
+ cache->ref--;
+ if (cache->ref)
+ return;
+ list_del(&cache->list);
+ free(cache->map);
+ free(cache);
+}
+
+static void *read_zpage(struct tracecmd_input *handle, int cpu, off64_t offset)
+{
+ struct cpu_data *cpu_data = &handle->cpu_data[cpu];
+ struct tracecmd_compress_chunk *chunk;
+ struct zchunk_cache *cache;
+ void *map = NULL;
+ int pindex;
+ int size;
+
+ /* Look in the cache of already loaded chunks */
+ list_for_each_entry(cache, &cpu_data->compress.cache, list) {
+ if (CHUNK_CHECK_OFFSET(cache->chunk, offset)) {
+ cache->ref++;
+ goto out;
+ }
+ }
+
+ chunk = get_zchunk(cpu_data, offset);
+ if (!chunk)
+ return NULL;
+ size = handle->page_size > chunk->size ? handle->page_size : chunk->size;
+ map = malloc(size);
+ if (!map)
+ return NULL;
+ if (tracecmd_uncompress_chunk(handle->compress, chunk, map) < 0)
+ goto error;
+
+ cache = calloc(1, sizeof(struct zchunk_cache));
+ if (!cache)
+ goto error;
+ cache->ref = 1;
+ cache->chunk = chunk;
+ cache->map = map;
+ list_add(&cache->list, &cpu_data->compress.cache);
+
+ /* a chunk can hold multiple pages, get the requested one */
+out:
+ pindex = (offset - cache->chunk->offset) / handle->page_size;
+ return cache->map + (pindex * handle->page_size);
+error:
+ free(map);
+ return NULL;
+}
+
static void *allocate_page_map(struct tracecmd_input *handle,
struct page *page, int cpu, off64_t offset)
{
@@ -1268,6 +1370,9 @@ static void *allocate_page_map(struct tracecmd_input *handle,
int ret;
int fd;
+ if (handle->cpu_compressed && handle->read_zpage)
+ return read_zpage(handle, cpu, offset);
+
if (handle->read_page) {
map = malloc(handle->page_size);
if (!map)
@@ -1410,6 +1515,8 @@ static void __free_page(struct tracecmd_input *handle, struct page *page)
if (handle->read_page)
free(page->map);
+ else if (handle->read_zpage)
+ free_zpage(cpu_data, page->map);
else
free_page_map(page->page_map);
@@ -3902,6 +4009,9 @@ struct tracecmd_input *tracecmd_alloc_fd(int fd, int flags)
/* By default, use usecs, unless told otherwise */
handle->flags |= TRACECMD_FL_IN_USECS;
+#ifdef INMEMORY_DECOMPRESS
+ handle->read_zpage = 1;
+#endif
if (do_read_check(handle, buf, 3))
goto failed_read;
--
2.31.1
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