blk/kernel: New perf counter to view amount of discard threads.

Signed-off-by: Igor Fedotov <[email protected]>

Author: ifed01

src/blk/kernel/KernelDevice.cc

@@ -96,6 +96,8 @@ KernelDevice::KernelDevice(CephContext* cct, aio_callback_t cb, void *cbpriv, ai
   b.set_prio_default(PerfCountersBuilder::PRIO_USEFUL);
   b.add_u64_counter(l_blk_kernel_device_discard_op, "discard_op",
             "Number of discard ops issued to kernel device");
+  b.add_u64_counter(l_blk_kernel_discard_threads, "discard_threads",
+            "Number of discard threads running");
 
   logger.reset(b.create_perf_counters());
   cct->get_perfcounters_collection()->add(logger.get());
@@ -601,6 +603,7 @@ void KernelDevice::_discard_update_threads(bool discard_stop)
       t->join();
     }
   }
+  logger->set(l_blk_kernel_discard_threads, discard_threads.size());
 }
 
 void KernelDevice::_discard_stop()

src/blk/kernel/KernelDevice.h

@@ -32,6 +32,7 @@
 enum {
   l_blk_kernel_device_first = 1000,
   l_blk_kernel_device_discard_op,
+  l_blk_kernel_discard_threads,
   l_blk_kernel_device_last,
 };