Re: [Qemu-block] [PATCH v5 00/10] qcow2: encryption threads

[Max Reitz]

On 02.04.19 17:37, Vladimir Sementsov-Ogievskiy wrote:
> v5: rebase on master, some conflicts resolved due to data-file feature
> 
> 01: new patch, just move test from cover letter to a file. I really hope that 
> it
>     will not hang the whole series, so, if we don't want it as is or with 
> really
>     tiny improvements, I'd prefer to skip it and queue 02-10 first.

Yup, noted.

> 09: "true" parameter added to moved qcow2_pre_write_overlap_check() call due 
> to
>     rebase on master (both before and after patch). Seems OK, so keep 
> Alberto's r-b.
> 
> performance:
> 
> after 01:
>  # ./tests/perf/block/qcow2/convert-to-encrypted /ssd/src.raw 
> /ssd/dst.enc.qcow2
> 14.18
>  # ./tests/perf/block/qcow2/convert-to-encrypted /ssd/src.raw 
> /ssd/dst.enc.qcow2 -W
> 13.77
> 
> after 10:
>  # ./tests/perf/block/qcow2/convert-to-encrypted /ssd/src.raw 
> /ssd/dst.enc.qcow2
> 14.35
>  # ./tests/perf/block/qcow2/convert-to-encrypted /ssd/src.raw 
> /ssd/dst.enc.qcow2 -W
> 5.62

Hm, I see those results as well:

Before:
w/o -W: 7.15
w/  -W: 6.77

After:
w/o -W: 7.19
w/  -W: 3.65


But with -t none, this is what I get:

Before:
w/o -W: 15.98
w/  -W: 10.91

After:
w/o -W: 19.95
w/  -W: 11.77


For good measure, on tmpfs:

Before:
w/o -W: 6.98
w/  -W: 6.75

After:
w/o -W: 7.04
w/  -W: 3.63


So it looks like the results with cache enabled are really only in the
cache.  When it goes down to disk, this series seems to decrease
performance.

To confirm whether that’s actually the case, I took another machine with
an SSD where I have more empty space and increased the size to 8 GB (not
the $size, because qemu-io doesn't like that, but well, yeah), and then
ran it again without cache:

Before:
w/o -W: ~50 - ~60 (varies...)
w/  -W: ~50 - ~70

After:
w/o -W: ~60
w/  -W: ~55 - ~85


So it does seem slower, although the values vary so much that it’s
difficult to tell.

Hmm...  And on that machine, there is no difference between before and
after when using -t none.  So I suppose it also depends on the device?



OK, I tried using qemu-img bench.  After patching it to accept --object,
these are the results I got with -t none -w on a preallocated (full) 8
GB image:

Before:
HDD: 17.7 s, 17.8 s, 18.0 s
SSD 1: 12.9 s, 15.8 s, 15.1 s
SSD 2: 1.8 s, 1.7 s, 1.7 s

After:
HDD: 16.1 s, 15.8 s, 15.8 s
SSD 1: 16.3 s, 18.0 s, 17.9 s
SSD 2: 2.0 s, 1.5 s, 1.5 s

Result #1: My SSD 1 is trash.

Result #2: I need more requests for SSD 2 to get a useful results.
Let's try again with 2^20:
Before: 23.8, 23.5, 23.3
After:  21.0, 20.6, 20.5

OK, and I can clearly see that this series increases the CPU usage
(which is good).


So...  Hm.  I suppose I conclude that this series decreases performance
on trashy SSDs?  But it gets better on my HDD and on my good SSD, so...
 Good thing I tested it, or something.

The only really interesting thing that came out of this is that I didn't
see an improvement with qemu-img convert (only on tmpfs), but that I do
see it with qemu-img bench.  So I'm wondering why you aren't using
qemu-img bench in the test in your first patch...?

Max

> Vladimir Sementsov-Ogievskiy (10):
>   tests/perf: Test qemu-img convert from raw to encrypted qcow2
>   qcow2.h: add missing include
>   qcow2: add separate file for threaded data processing functions
>   qcow2-threads: use thread_pool_submit_co
>   qcow2-threads: qcow2_co_do_compress: protect queuing by mutex
>   qcow2-threads: split out generic path
>   qcow2: qcow2_co_preadv: improve locking
>   qcow2: qcow2_co_preadv: skip using hd_qiov when possible
>   qcow2: bdrv_co_pwritev: move encryption code out of the lock
>   qcow2: do encryption in threads
> 
>  block/qcow2.h                               |  20 +-
>  block/qcow2-bitmap.c                        |   1 -
>  block/qcow2-cache.c                         |   1 -
>  block/qcow2-cluster.c                       |   8 +-
>  block/qcow2-refcount.c                      |   1 -
>  block/qcow2-snapshot.c                      |   1 -
>  block/qcow2-threads.c                       | 268 +++++++++++++++++++
>  block/qcow2.c                               | 275 ++++----------------
>  block/Makefile.objs                         |   2 +-
>  tests/perf/block/qcow2/convert-to-encrypted |  48 ++++
>  10 files changed, 389 insertions(+), 236 deletions(-)
>  create mode 100644 block/qcow2-threads.c
>  create mode 100755 tests/perf/block/qcow2/convert-to-encrypted
>

signature.asc
Description: OpenPGP digital signature