Begin forwarded message: Date: Tue, 19 Nov 2019 09:52:12 +0000 From: bugzilla-daemon@xxxxxxxxxxxxxxxxxxx To: stephen@xxxxxxxxxxxxxxxxxx Subject: [Bug 205579] New: rfcomm causes very high cpu usage during serial connectivity https://bugzilla.kernel.org/show_bug.cgi?id=205579 Bug ID: 205579 Summary: rfcomm causes very high cpu usage during serial connectivity Product: Networking Version: 2.5 Kernel Version: Everything Hardware: All OS: Linux Tree: Mainline Status: NEW Severity: normal Priority: P1 Component: Other Assignee: stephen@xxxxxxxxxxxxxxxxxx Reporter: epigramx@xxxxxxxxx Regression: No This appears to be a long standing issue that is mentioned only in old Debian bug reports and current Raspbian discussions but it remains important for embedded systems because they are not powerful systems. Sources: https://bugs.debian.org/cgi-bin/bugreport.cgi?bug=565485 https://www.raspberrypi.org/forums/viewtopic.php?t=181796 Issue Description: "I use 'rfcomm listen' in combination with 'gpspipe' to relay GPS data from my eeePC to my Blackberry. I noticed, however, that the CPU overhead from 'rfcomm listen' is quite significant -- over 10% on my eeePC 901. Running 'strace' reveals that rfcomm is in a tight loop between 'waitpid' (with WNOHANG) and 'ppoll' (with a 200 nanosecond(!!) timeout). This is evidently the source of the extreme CPU usage. If it's critical that rfcomm know the child has died ASAP, I would expect it should be watching for the SIGCHLD signal rather than trying to use waitpid(). If it's not all that critical, it probably doesn't need to be watching for child death at a rate of five millions checks per second. :)" also "I am experimenting with a serial connection to Pi Zero W using the on-board Bluetooth module. I can successfully establish a connection and send data to Pi. However as soon as the connection starts, the rfcomm process consumes almost 50% of the processor (as top shows). This noticeably slows down other processes." The issue remains on current code. -- You are receiving this mail because: You are the assignee for the bug.
