Methods and arrangements for collecting tracing data from a plurality of threads of a program. A storage buffer is provided, a first number of units of tracing data for a first thread of the program is determined, and a second number of units of tracing data for a second thread of the program is determined. In the storage buffer, a first block of storage space is reserved for storing the first number of units of tracing data and a second block of storage space is reserved for storing the second number of units of tracing data. Tracing data are then written concurrently into the first and blocks.