Hi Stefan, This solve the bug seen by the customer. Whole patchset tested by on behalf of the user.
Tested-By: Benoit Canet <ben...@irqsave.net> Best regards Benoît > Le Thursday 21 Mar 2013 à 15:49:55 (+0100), Stefan Hajnoczi a écrit : > Benoît Canet <ben...@irqsave.net> reported that QEMU I/O throttling can > oscillate under continuous I/O. The test case runs 50 threads performing > random writes and a -drive iops=150 limit is used. > > Since QEMU I/O throttling is implemented using 100 millisecond time slices, > we'd expect 150 +/- 15 IOPS. Anything outside that range indicates a problem > with the I/O throttling algorithm. > > It turned out that even a single thread performing sequential I/O continuously > is throttled outside the 150 +/- 15 IOPS range. The continous stream of I/O > slows down as time goes on but resets to 150 IOPS again when interrupted. > This > can be tested with: > > $ iostat -d 1 -x /dev/vdb & > $ dd if=/dev/vdb of=/dev/null bs=4096 iflag=direct > > This patches addresses these problems as follows: > > 1. Account for I/O requests when they are submitted instead of completed. > This > ensures that we do not exceed the budget for this slice. Exceeding the > budget leads to fluctuations since we have to make up for this later. > > 2. Use constant 100 millisecond slice time. Adjusting the slice time at > run-time led to oscillations. Since the reason for adjusting slice time is > not clear, drop this behavior. > > I have also included two code clean-up patches. > > Benoît: Please let me know if this solves the problems you're seeing. > > Stefan Hajnoczi (4): > block: fix I/O throttling accounting blind spot > block: keep I/O throttling slice time constant > block: drop duplicated slice extension code > block: clean up I/O throttling wait_time code > > block.c | 47 > ++++++++++++++++++++--------------------------- > blockdev.c | 1 - > include/block/block_int.h | 3 +-- > 3 files changed, 21 insertions(+), 30 deletions(-) > > -- > 1.8.1.4 >
