test/crimson: cbt test does rand-reads instead of seq-reads.

The rationale behind the change is not only that random
read performance tends to be more important and meaningful.
Actually, the current procedure is broken because of how
`rados bench` internally operates: the number of seq read
operations is limited by the number of write ops used to
create the data set (`write` with the `--no-cleanup` option):

  ```cpp
  int ObjBencher::write_bench(/* ... */) {
    // ...
    //write object size/number data for read benchmarks
    encode(data.object_size, b_write);
    encode(data.finished, b_write);

    //...

  int ObjBencher::fetch_bench_metadata(// ...
                                       int* num_ops, /* ... */) {
    // ...
    decode(*object_size, p);
    decode(*num_ops, p);

  int ObjBencher::seq_read_bench(
    int seconds_to_run, int num_ops, int num_objects,
    int concurrentios, int pid, bool no_verify) {

    // ...

    //start initial reads
    for (int i = 0; i < concurrentios; ++i) {
      // ...
      ++data.started;
    }

    // ...

    while ((seconds_to_run && mono_clock::now() < finish_time) &&
           num_ops > data.started) {
  ```

This makes significant problem as the cbt test uses short (3 sec.)
period of prefill. In the consequence, the sequential read testing
takes around half-second.

Signed-off-by: Radoslaw Zarzynski <rzarzyns@redhat.com>

diff --git a/src/test/crimson/cbt/radosbench_4K_read.yaml b/src/test/crimson/cbt/radosbench_4K_read.yaml
index d4205d710e0e11b23276f543cc2c0e65e43ba080..db21f7a4df27894df372930bc8bd3c5e798f6720 100644 (file)
--- a/src/test/crimson/cbt/radosbench_4K_read.yaml
+++ b/src/test/crimson/cbt/radosbench_4K_read.yaml
@@ -13,6 +13,7 @@ tasks:
         pool_profile: 'replicated'
         read_time: 30
         read_only: true
+        readmode: 'rand'
         prefill_time: 3
         acceptable:
           bandwidth: '(or (greater) (near 0.05))'