Hi Anthony,
> There's an aio_init in block-raw-posix.c that sets the thread count to
> 1. If you #if 0 out that block, or increase the threads to something
> higher (like 16), you should see multiple simultaneous requests. Sorry
> about that, I had that in a different patch in my tree.
Thank you for your suggestion. I tried commenting out the calling
aio_init(), the AIO functions use aio_threads=20 and aio_num=64 as
default, but the results were the same as I have tested before, the
number of I/Os was divided into equal proportion.
Then, I changed "io_throttle" value to 1(default is 4). "io_throttle"
is a dm-ioband's configuration parameter, when the number of BIOs in
progress exceeds this value, dm-ioband starts to control the bandwidth.
And then the bandwidth control seemed to work much better, but sometimes
I wasn't able to get the proper proportions. As these results indicate,
the number of simultaneous I/O requests issued from two KVM virtual
machines was less than 4.
The number of issued I/Os for 60 seconds (io_throttle = 1)
--------------------------------------------------------
| weight setting | sda11 | sda12 | total |
| sda11 : sda12 | I/Os(%) | I/Os(%) | I/Os |
|-----------------+--------------+-------------|---------|
| 80:20 #1 | 7264(75.8%) | 2324(24.2%) | 9588 |
| 80:20 #2 | 7147(71.1%) | 2899(28.9%) | 10046 |
|-----------------+--------------+-------------|---------|
| 50:50 #1 | 5162(55.5%) | 4146(44.5%) | 9308 |
| 50:50 #2 | 4666(49.3%) | 4793(50.7%) | 9459 |
|-----------------+--------------+-------------|---------|
| 20:80 #1 | 3574(39.8%) | 5402(60.2%) | 8976 |
| 20:80 #2 | 2038(21.4%) | 7499(78.6%) | 9537 |
|-----------------+--------------+-------------|---------|
| 10:90 #1 | 2027(21.1%) | 7602(78.9%) | 9629 |
| 10:90 #2 | 1556(16.4%) | 7935(83.6%) | 9491 |
--------------------------------------------------------
> The virtio block backend isn't quite optimal right now. I have some
> patches (that are currently suffering bitrot) that switch over to
> linux-aio which allows zero-copy and for proper barrier support (so the
> guest block device will use an ordered queue). The QEMU aio
> infrastructure makes it tough to integrate it properly though.
That's good idea. I hope your work is going well and look forward to
releasing the patches.
Thanks,
Ryo Tsuruta
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