On Jul 5, 2024, at 1:32 AM, Liu, Yuan1 <yuan1.liu@intel.com> wrote:
-----Original Message-----
From: Peter Xu <peterx@redhat.com>
Sent: Thursday, July 4, 2024 11:36 PM
To: Liu, Yuan1 <yuan1.liu@intel.com>
Cc: Wang, Yichen <yichen.wang@bytedance.com>; Paolo Bonzini
<pbonzini@redhat.com>; Daniel P. Berrangé <berrange@redhat.com>; Eduardo
Habkost <eduardo@habkost.net>; Marc-André Lureau
<marcandre.lureau@redhat.com>; Thomas Huth <thuth@redhat.com>; Philippe
Mathieu-Daudé <philmd@linaro.org>; Fabiano Rosas <farosas@suse.de>; Eric
Blake <eblake@redhat.com>; Markus Armbruster <armbru@redhat.com>; Laurent
Vivier <lvivier@redhat.com>; qemu-devel@nongnu.org; Hao Xiang
<hao.xiang@linux.dev>; Zou, Nanhai <nanhai.zou@intel.com>; Ho-Ren (Jack)
Chuang <horenchuang@bytedance.com>
Subject: Re: [PATCH v3 0/4] Implement using Intel QAT to offload ZLIB
On Thu, Jul 04, 2024 at 03:15:51AM +0000, Liu, Yuan1 wrote:
-----Original Message-----
From: Peter Xu <peterx@redhat.com>
Sent: Wednesday, July 3, 2024 3:16 AM
To: Wang, Yichen <yichen.wang@bytedance.com>
Cc: Paolo Bonzini <pbonzini@redhat.com>; Daniel P. Berrangé
<berrange@redhat.com>; Eduardo Habkost <eduardo@habkost.net>; Marc-
André
Lureau <marcandre.lureau@redhat.com>; Thomas Huth <thuth@redhat.com>;
Philippe Mathieu-Daudé <philmd@linaro.org>; Fabiano Rosas
<farosas@suse.de>; Eric Blake <eblake@redhat.com>; Markus Armbruster
<armbru@redhat.com>; Laurent Vivier <lvivier@redhat.com>; qemu-
devel@nongnu.org; Hao Xiang <hao.xiang@linux.dev>; Liu, Yuan1
<yuan1.liu@intel.com>; Zou, Nanhai <nanhai.zou@intel.com>; Ho-Ren
(Jack)
Chuang <horenchuang@bytedance.com>
Subject: Re: [PATCH v3 0/4] Implement using Intel QAT to offload ZLIB
On Thu, Jun 27, 2024 at 03:34:41PM -0700, Yichen Wang wrote:
v3:
- Rebase changes on top of master
- Merge two patches per Fabiano Rosas's comment
- Add versions into comments and documentations
v2:
- Rebase changes on top of recent multifd code changes.
- Use QATzip API 'qzMalloc' and 'qzFree' to allocate QAT buffers.
- Remove parameter tuning and use QATzip's defaults for better
performance.
- Add parameter to enable QAT software fallback.
v1:
https://lists.nongnu.org/archive/html/qemu-devel/2023-
12/msg03761.html
* Performance
We present updated performance results. For circumstantial reasons,
v1
presented performance on a low-bandwidth (1Gbps) network.
Here, we present updated results with a similar setup as before but
with
two main differences:
1. Our machines have a ~50Gbps connection, tested using 'iperf3'.
2. We had a bug in our memory allocation causing us to only use ~1/2
of
the VM's RAM. Now we properly allocate and fill nearly all of the
VM's
RAM.
Thus, the test setup is as follows:
We perform multifd live migration over TCP using a VM with 64GB
memory.
We prepare the machine's memory by powering it on, allocating a
large
amount of memory (60GB) as a single buffer, and filling the buffer
with
the repeated contents of the Silesia corpus[0]. This is in lieu of a
more
realistic memory snapshot, which proved troublesome to acquire.
We analyze CPU usage by averaging the output of 'top' every second
during migration. This is admittedly imprecise, but we feel that it
accurately portrays the different degrees of CPU usage of varying
compression methods.
We present the latency, throughput, and CPU usage results for all of
the
compression methods, with varying numbers of multifd threads (4, 8,
and
16).
[0] The Silesia corpus can be accessed here:
https://sun.aei.polsl.pl//~sdeor/index.php?page=silesia
** Results
4 multifd threads:
|---------------|---------------|----------------|---------|----
----
-|
|method |time(sec) |throughput(mbps)|send cpu%|recv
cpu%|
|---------------|---------------|----------------|---------|----
----
-|
|qatzip | 23.13 | 8749.94 |117.50
|186.49
|
|---------------|---------------|----------------|---------|----
----
-|
|zlib |254.35 | 771.87 |388.20
|144.40
|
|---------------|---------------|----------------|---------|----
----
-|
|zstd | 54.52 | 3442.59 |414.59
|149.77
|
|---------------|---------------|----------------|---------|----
----
-|
|none | 12.45 |43739.60 |159.71
|204.96
|
|---------------|---------------|----------------|---------|----
----
-|
8 multifd threads:
|---------------|---------------|----------------|---------|----
----
-|
|method |time(sec) |throughput(mbps)|send cpu%|recv
cpu%|
|---------------|---------------|----------------|---------|----
----
-|
|qatzip | 16.91 |12306.52 |186.37
|391.84
|
|---------------|---------------|----------------|---------|----
----
-|
|zlib |130.11 | 1508.89 |753.86
|289.35
|
|---------------|---------------|----------------|---------|----
----
-|
|zstd | 27.57 | 6823.23 |786.83
|303.80
|
|---------------|---------------|----------------|---------|----
----
-|
|none | 11.82 |46072.63 |163.74
|238.56
|
|---------------|---------------|----------------|---------|----
----
-|
16 multifd threads:
|---------------|---------------|----------------|---------|----
----
-|
|method |time(sec) |throughput(mbps)|send cpu%|recv
cpu%|
|---------------|---------------|----------------|---------|----
----
-|
|qatzip |18.64 |11044.52 | 573.61
|437.65
|
|---------------|---------------|----------------|---------|----
----
-|
|zlib |66.43 | 2955.79 |1469.68
|567.47
|
|---------------|---------------|----------------|---------|----
----
-|
|zstd |14.17 |13290.66 |1504.08
|615.33
|
|---------------|---------------|----------------|---------|----
----
-|
|none |16.82 |32363.26 | 180.74
|217.17
|
|---------------|---------------|----------------|---------|----
----
-|
** Observations
- In general, not using compression outperforms using compression in
a
non-network-bound environment.
- 'qatzip' outperforms other compression workers with 4 and 8
workers,
achieving a ~91% latency reduction over 'zlib' with 4 workers, and
a
~58% latency reduction over 'zstd' with 4 workers.
- 'qatzip' maintains comparable performance with 'zstd' at 16
workers,
showing a ~32% increase in latency. This performance difference
becomes more noticeable with more workers, as CPU compression is
highly
parallelizable.
- 'qatzip' compression uses considerably less CPU than other
compression
methods. At 8 workers, 'qatzip' demonstrates a ~75% reduction in
compression CPU usage compared to 'zstd' and 'zlib'.
- 'qatzip' decompression CPU usage is less impressive, and is even
slightly worse than 'zstd' and 'zlib' CPU usage at 4 and 16
workers.
Thanks for the results update.
It looks like the docs/migration/ file is still missing. It'll be
great
to
have it in the next version or separately.
So how it compares with QPL (which got merged already)? They at least
look
like both supported on an Intel platform, so an user whoever wants to
compress the RAM could start to look at both. I'm utterly confused on
why
Intel provides these two similar compressors. It would be great to
have
some answer and perhaps put into the doc.
Yuan,
I would like to explain some of the reasons why we want to merge the
two QAT and IAA solutions into the community.
Yes, these are very helpful information. Please consider putting them
into
the cover letter if there's a repost, and perhaps also in the doc/ files.
1. Although Intel Xeon Sapphire Rapids supports both QAT and IAA,
different
SKUs support different numbers of QAT and IAA, so some users do not
have
both QAT and IAA at the same time.
2. QAT products include PCIe cards, which are compatible with older Xeon
products and other non-Xeon products. And some users have already
used QAT
cards to accelerate live migration.
Ah, this makes some sense to me.
So a previous question always haunted me, where I wondered why an user who
bought all these fancy and expensive processors with QAT, would still like
to not invest on a better network of 50G or more, but stick with 10Gs
ancient NICs and switches.
So what you're saying is logically in some old clusters with old chips and
old network solutions, it's possible that user buys these PCIe cards
separately so it may help with that old infra migrate VMs faster. Is that
the case?
Yes, users do not add a QAT card just for live migration. Users mainly use QAT-SRIOV technology to help cloud users offload compression and encryption.If so, we may still want some numbers showing how this performs in a
network-limited environment, and how that helps users to migrate. Sorry
if
there's some back-and-forth requirement asking for these numbers, but I
think these are still important information when an user would like to
decide whether to use these features. Again, put that into docs/ if
proper
would be nice too.
Yes, I will provide some performance data at some specific bandwidths(100Mbps/1Gbps/10Gbps). And add documentation to explain the advantages of using QAT
Just want to add some information here. So in ByteDance, the current generation server is quipped with 2*100Gb NIC. We reserve 10Gbps for control plane purposes which includes live migration here. So it is not about we are using “good network”, it is about not normal to use full bandwidth for control plane purposes. Hence we do have a requirements for QAT/IAA in these cases.
3. In addition to compression, QAT and IAA also support various other
features
to better serve different workloads. Here is an introduction to the
accelerators,
including usage scenarios of QAT and IAA.
https://www.intel.com/content/dam/www/central-
libraries/us/en/documents/2022-12/storage-engines-4th-gen-xeon-brief.pdf
Thanks for the link.
However this doesn't look like a reason to support it in migration? It
needs to help migration in some form or another, no matter how many
features it provides.. since migration may not consume them.
Two major (but pure..) questions:
1) Why high cpu usage?
I raised this question below [1] too but I didn't yet get an answer.
Ror 8-chan multifd, it's ~390% (QAT) v.s. ~240% (nocomp), even if
46Gbps bw for the latter... so when throttled it will be even lower?
The paper you provided above has this upfront:
When a CPU can offload storage functions to built-in accelerators,
it frees up cores for business-critical workloads...
Isn't that a major feature to be able to "offload" things? Why cpu
isn't freed even if the offload happened?
Yes, it doesn't make sense, I will check this. 2) TLS?
I think I asked before, I apologize if any of you've already answered
and if I forgot.. but have any of you looked into offload TLS
(instead
of compression) with the QATs?
I'm sorry for not responding to the previous question about TLS. QAT has many related success cases (for example, OpenSSL). https://www.intel.com/content/dam/www/public/us/en/documents/solution-briefs/accelerating-openssl-brief.pdfI will send a separate RFC or patch about this part because the software stacks of QAT compression and encryption are independent, so we discuss them separately.Thanks,
For users who have both QAT and IAA, we recommend the following for
choosing a
live migration solution:
1. If the number of QAT devices is equal to or greater than the number
of IAA devices
and network bandwidth is limited, it is recommended to use the
QATZip(QAT) solution.
2. In other scenarios, the QPL (IAA) solution can be used first.
I am honestly curious too on whether are you planning to use it in
production. It looks like if the network resources are rich, no-comp
is
mostly always better than qatzip, no matter on total migration time or
cpu
consumption. I'm pretty surprised that it'll take that much resources
even
if the work should have been offloaded to the QAT chips iiuc.
[1]
I think it may not be a problem to merge this series even if it
performs
slower at some criterias.. but I think we may still want to know when
this
should be used, or the good reason this should be merged (if it's not
about
it outperforms others).
Thanks,
Bryan Zhang (4):
meson: Introduce 'qatzip' feature to the build system
migration: Add migration parameters for QATzip
migration: Introduce 'qatzip' compression method
tests/migration: Add integration test for 'qatzip' compression
method
hw/core/qdev-properties-system.c | 6 +-
meson.build | 10 +
meson_options.txt | 2 +
migration/meson.build | 1 +
migration/migration-hmp-cmds.c | 8 +
migration/multifd-qatzip.c | 382
+++++++++++++++++++++++++++++++
migration/multifd.h | 1 +
migration/options.c | 57 +++++
migration/options.h | 2 +
qapi/migration.json | 38 +++
scripts/meson-buildoptions.sh | 6 +
tests/qtest/meson.build | 4 +
tests/qtest/migration-test.c | 35 +++
13 files changed, 551 insertions(+), 1 deletion(-)
create mode 100644 migration/multifd-qatzip.c
--
Yichen Wang
--
Peter Xu
--
Peter Xu
|