On 29/11/19 12:44:53, Bernd Schubert wrote: > >> Trace attached. Produced by: start the trace script > >> (with the pendrive already plugged), wait some seconds, run the test > >> (1 trial, 1 GB), wait for the test to finish, stop the trace. > >> > >> The copy took 73 seconds, roughly as already seen before with the fast > >> old kernel. > > > > This trace shows a good write IO order because the writeback IOs are > > queued to block layer serially from the 'cp' task and writeback wq. > > > > However, writeback IO order is changed in current linus tree because > > the IOs are queued to block layer concurrently from the 'cp' task > > and writeback wq. It might be related with killing queue_congestion > > by blk-mq. > > What about using direct-io to ensure order is guaranteed? Pity that 'cp' > doesn't seem to have an option for it. But dd should do the trick. > Andrea, can you replace cp with a dd command (on the slow kernel)? > > dd if=<path-to-src-file> of=<path-to-copy-on-flash-device> bs=1M > oflag=direct On the "new bad patched" kernel, this command take 68 seconds to complete (mean on 100 trials, with a narrow standard deviation), so perfectly aligned with the cp command on the old fast good kernel. Thanks, and bye Andrea
