Hello, Sorry about the delay. On Wed, Feb 26, 2020 at 08:59:55PM +0100, Miklos Szeredi wrote: > - apparently memcpy is copying downwards (from largest address to > smallest address). Not sure why, when I run the reproducer, it copies > upwards. > - there's a slow batch of reads of the first ~4MB of data, then a > quick writeback > - there's a quick read of the rest (~95MB) of data, then a quick > writeback of the same > > Plots of the whole and closeups of slow and quick segments attached. > X axis is time, Y axis is offset. > > Tejun, could this behavior be attributed to dirty throttling? What > would be the best way to trace this? Yeah, seems likely. Can you please try offcputime (or just sample /proc/PID/stack) and see whether it's in balance dirty pages? https://github.com/iovisor/bcc/blob/master/tools/offcputime.py If it's dirty throttling, the next step would be watching the bdp tracepoints to find out what kind of numbers it's getting. Thanks. -- tejun
