[PATCH] rt-tests: hwlatdetect: Gracefully handle lack of /dev/cpu_dma_latency

Punit Agrawal
2021-09-28T08:17:28Z

From: Punit Agrawal <punit1.agrawal@toshiba.co.jp>

On systems where cpu idle is disabled to reduce latencies,
"/dev/cpu_dma_latency" does not exist and leads to the following
exception report from python when using hwlatdetect.py -

FileNotFoundError: [Errno 2] No such file or directory: '/dev/cpu_dma_latency

Update hwlatdetect to check whether the file exists before attemping
to write values to it.

Reported-by: Suresh Hegde <suresh1.hegde@toshiba.co.jp>
Signed-off-by: Punit Agrawal <punit1.agrawal@toshiba.co.jp>
---
src/hwlatdetect/hwlatdetect.py | 7 +++++--
1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/src/hwlatdetect/hwlatdetect.py b/src/hwlatdetect/hwlatdetect.py
index 12228f45f852..89537a6e371f 100755
--- a/src/hwlatdetect/hwlatdetect.py
+++ b/src/hwlatdetect/hwlatdetect.py
@@ -216,8 +216,11 @@ class Detector(object):
# use c_states_on() to close the file descriptor and re-enable c-states
#
def c_states_off(self):
- self.dma_latency_handle = os.open("/dev/cpu_dma_latency", os.O_WRONLY)
- os.write(self.dma_latency_handle, b'\x00\x00\x00\x00')
+ if os.path.exists("/dev/cpu_dma_latency"):
+ self.dma_latency_handle = os.open("/dev/cpu_dma_latency", os.O_WRONLY)
+ os.write(self.dma_latency_handle, b'\x00\x00\x00\x00')
+ else:
+ self.dma_latency_handle = None
debug("c-states disabled")

def c_states_on(self):
--
2.32.0