Deep Dive on Amazon EC2 Instances (March 2017)

© 2017, Amazon Web Services, Inc. or its Affiliates. All rights reserved.
Deep Dive on Amazon EC2 Instances
Featuring Performance Optimization Best Practices
Julien Simon
Principal Technical Evangelist, AWS
julsimon@amazon.fr
@julsimon

What to Expect from the Session
§  Understanding the factors that going into choosing an EC2 instance
§  Defining system performance and how it is characterized for
different workloads
§  How Amazon EC2 instances deliver performance while providing
flexibility and agility
§  How to make the most of your EC2 instance experience through the
lens of several instance types

API
EC2
EC2
Amazon Elastic Compute Cloud Is Big
Instances
Networking
Purchase options

Host Server
Hypervisor
Guest 1 Guest 2 Guest n
Amazon EC2 Instances

In the past
§  First launched in August 2006
§  M1 instance
§  “One size fits all”
M1

Amazon EC2 Instances History
2006 2008 2010 2012 2014
m1.small
m1.large
m1.xlarge
c1.medium
c1.xlarge
m2.xlarge
m2.4xlarge
m2.2xlarge
cc1.4xlarge
t1.micro
cg1.4xlarge
cc2.8xlarge
m1.medium
hi1.4xlarge
m3.xlarge
m3.2xlarge
hs1.8xlarge
cr1.8xlarge
c3.large
c3.xlarge
c3.2xlarge
c3.4xlarge
c3.8xlarge
g2.2xlarge
i2.xlarge
i2.2xlarge
i2.4xlarge
i2.4xlarge
m3.medium
m3.large
r3.large
r3.xlarge
r3.2xlarge
r3.4xlarge
r3.8xlarge
t2.micro
t2.small
t2.med
c4.large
c4.xlarge
c4.2xlarge
c4.4xlarge
c4.8xlarge
d2.xlarge
d2.2xlarge
d2.4xlarge
d2.8xlarge
g2.8xlarge
t2.large
m4.large
m4.xlarge
m4.2xlarge
m4.4xlarge
m4.10xlarge
x1.32xlarge
t2.nano
m4.16xlarge
p2.xlarge
p2.8xlarge
p2.16xlarge
t2.xlarge
t2.2xlarge
r4.large
r4.xlarge
r4.2xlarge
r4.4xlarge
r4.8xlarge
r4.16xlarge
2016
x1.16xlarge
i3.large
i3.xlarge
i3.2xlarge
i3.4xlarge
i3.8xlarge
i3.16xlarge

Instance generation
c4.xlarge
Instance family Instance size

EC2 Instance Families
General
purpose
Compute
optimized
C3
Storage and I/O
optimized
I2
P2
GPU
optimized
Memory
optimized
R3
C4
M4
D2
X1
G2

What’s a Virtual CPU? (vCPU)
§  A vCPU is typically a hyper-threaded physical core*
§  On Linux, “A” thread ids enumerated before “B” thread ids
§  A: 0-3, B: 4-7
§  On Windows, thread ids are interleaved
§  A: 0, 2, 4, 6. B : 1, 3, 5, 7
§  Divide vCPU count by 2 to get core count
§  Cores by EC2 & RDS DB Instance type:
https://aws.amazon.com/ec2/virtualcores/
§  “Demystifying the Number of vCPUs for Optimal Workload Performance”
https://d0.awsstatic.com/whitepapers/Demystifying_vCPUs.pdf
* Except on the “t” family and m3.medium

‘lstopo’ output for m4.10xlarge: 40 threads and 20 physical cores

Disable Hyper-Threading If You Need To
§  Useful for FPU heavy applications
Linux
§  Use ‘lscpu’ to validate layout
§  Hot offline the “B” threads
for i in `seq 64 127`; do
echo 0 > /sys/devices/system/cpu/cpu${i}/online
done
§  Set grub to only initialize the first half of
all threads
maxcpus=63
[ec2-user@ip-172-31-7-218 ~]$ lscpu
CPU(s): 128
On-line CPU(s) list: 0-127
Thread(s) per core: 2
Core(s) per socket: 16
Socket(s): 4
NUMA node(s): 4
Model name: Intel(R) Xeon(R) CPU
Hypervisor vendor: Xen
Virtualization type: full
NUMA node0 CPU(s): 0-15,64-79
NUMA node1 CPU(s): 16-31,80-95
NUMA node2 CPU(s): 32-47,96-111
NUMA node3 CPU(s): 48-63,112-127
Windows
§  More complicated due to
interleaved thread ids
§  Use “CPU affinity”

‘lstopo’ output for m4.10xlarge with HT disabled: 20 threads and 20 physical cores

Instance sizing
c4.8xlarge 2 - c4.4xlarge
≈
4 - c4.2xlarge
≈
8 - c4.xlarge
≈

Resource Allocation
§  All resources assigned to you are dedicated to your instance with no
over commitment*
§  All vCPUs are dedicated to you
§  Memory allocated is assigned only to your instance
§  Network resources are partitioned to avoid “noisy neighbors”
§  Curious about the number of instances per host? Use “Dedicated
Hosts” as a guide.
*Again, the “t” family is special

“Launching new instances and running tests
in parallel is easy…[when choosing an
instance] there is no substitute for measuring
the performance of your full application.”
- EC2 documentation

Timekeeping Explained
§  Timekeeping in an instance is deceptively hard
§  gettimeofday(), clock_gettime(), QueryPerformanceCounter()
§  Xen clock
§  Handled by the Xen hypervisor
•  Does not support vDSO (virtual dynamic shared object)
à Requires a system call, leading to context switches, etc. à Slow
§  Time Stamp Counter (TSC)
§  CPU counter, accessible from userspace through vDSO à Much faster
§  Available on Sandy Bridge processors and newer
§  On current generation instances, use TSC as clocksource

Benchmarking - Time Intensive Application
#include <sys/time.h>
#include <time.h>
#include <stdio.h>
#include <unistd.h>
int main()
{
time_t start,end;
time (&start);
for ( int x = 0; x < 100000000; x++ ) {
float f;
float g;
float h;
f = 123456789.0f;
g = 123456789.0f;
h = f * g;
struct timeval tv;
gettimeofday(&tv, NULL);
}
time (&end);
double dif = difftime (end,start);
printf ("Elasped time is %.2lf seconds.n", dif );
return 0;
}

Using the Xen Clock Source
[centos@ip-192-168-1-77 testbench]$ strace -c ./test
Elasped time is 12.00 seconds.
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
99.99 3.322956 2 2001862 gettimeofday
0.00 0.000096 6 16 mmap
0.00 0.000050 5 10 mprotect
0.00 0.000038 8 5 open
0.00 0.000026 5 5 fstat
0.00 0.000025 5 5 close
0.00 0.000023 6 4 read
0.00 0.000008 8 1 1 access
0.00 0.000006 6 1 brk
0.00 0.000006 6 1 execve
0.00 0.000005 5 1 arch_prctl
0.00 0.000000 0 1 munmap
------ ----------- ----------- --------- --------- ----------------
100.00 3.323239 2001912 1 total

Using the TSC Clock Source
[centos@ip-192-168-1-77 testbench]$ strace -c ./test
Elasped time is 2.00 seconds.
% time seconds usecs/call calls errors syscall
------ ----------- ----------- --------- --------- ----------------
32.97 0.000121 7 17 mmap
20.98 0.000077 8 10 mprotect
11.72 0.000043 9 5 open
10.08 0.000037 7 5 close
7.36 0.000027 5 6 fstat
6.81 0.000025 6 4 read
2.72 0.000010 10 1 munmap
2.18 0.000008 8 1 1 access
1.91 0.000007 7 1 execve
1.63 0.000006 6 1 brk
1.63 0.000006 6 1 arch_prctl
0.00 0.000000 0 1 write
------ ----------- ----------- --------- --------- ----------------
100.00 0.000367 53 1 total

Change with:
Tip: Use TSC as clocksource

P-state and C-state Control
§  c4.8xlarge, d2.8xlarge, m4.10xlarge, m4.16xlarge,
p2.16xlarge, x1.16xlarge, x1.32xlarge
§  By entering deeper idle states, non-idle cores can
achieve up to 300MHz higher clock frequencies
§  But… deeper idle states require more time to exit,
may not be appropriate for latency-sensitive
workloads
§  Limit c-state by adding “intel_idle.max_cstate=1” to grub
https://aws.amazon.com/blogs/aws/now-available-new-c4-instances/
http://docs.aws.amazon.com/AWSEC2/latest/UserGuide/processor_state_control.html

Tip: P-state Control for AVX2
§  If an application makes heavy use of AVX2 on all cores, the processor
may attempt to draw more power than it should
§  Processor will transparently reduce frequency
§  Frequent changes of CPU frequency can slow an application
sudo sh -c "echo 1 > /sys/devices/system/cpu/intel_pstate/no_turbo"

Review: T2 Instances
§  Lowest cost EC2 instance at $0.0059 per hour
§  Burstable performance
§  Fixed allocation enforced with CPU credits
Model vCPU Baseline CPU
Credits /
Hour
Memory
(GiB)
Storage
t2.nano 1 5% 3 .5 EBS Only
t2.micro 1 10% 6 1 EBS Only
t2.small 1 20% 12 2 EBS Only
t2.medium 2 40%** 24 4 EBS Only
t2.large 2 60%** 36 8 EBS Only
General purpose, web serving, developer environments, small databases

How Credits Work
§  A CPU credit provides the performance of a
full CPU core for one minute
§  An instance earns CPU credits at a steady rate
§  An instance consumes credits when active
§  Credits expire (leak) after 24 hours
Baseline rate
Credit
balance
Burst
rate

Tip: Monitor CPU Credit Balance

Review: X1 Instances
§  Largest memory instance with 2 TB of DRAM
§  Quad socket, Intel E7 processors with 128 vCPUs
Model vCPU Memory (GiB) Local Storage Network
x1.16xlarge 64 976 1x 1920GB SSD 10Gbps
x1.32xlarge 128 1952 2x 1920GB SSD 20Gbps
In-memory databases, big data processing, HPC workloads

NUMA
§  Non-uniform memory access
§  Each processor in a multi-CPU system has
local memory that is accessible through a
fast interconnect
§  Each processor can also access memory
from other CPUs, but local memory access
is a lot faster than remote memory
§  Performance is related to the number of
CPU sockets and how they are connected -
Intel QuickPath Interconnect (QPI)

QPI
122GB 122GB
16 vCPU’s 16 vCPU’s
r3.8xlarge

QPI
QPI
QPIQPI
QPI
488GB
488GB
488GB
488GB
x1.32xlarge

Tip: Kernel Support for NUMA Balancing
§  An application will perform best when the threads of its processes are
accessing memory on the same NUMA node.
§  NUMA balancing moves tasks closer to the memory they are accessing.
§  This is all done automatically by the Linux kernel when automatic NUMA
balancing is active: version 3.8+ of the Linux kernel.
§  Windows support for NUMA first appeared in the Enterprise and Data
Center SKUs of Windows Server 2003.
§  Set “numa=off” or use numactl to reduce NUMA paging if your
application uses more memory than will fit on a single socket or has
threads that move between sockets

Operating Systems Impact Performance
§  Memory intensive web application
§  Created many threads
§  Rapidly allocated/deallocated memory
§  Comparing performance of RHEL6 vs RHEL7
§  Notice high amount of “system” time in top
§  Found a benchmark tool (ebizzy) with a similar performance profile
§  Traced it’s performance with “perf”
https://sourceforge.net/projects/ebizzy/
https://perf.wiki.kernel.org

On RHEL6
[ec2-user@ip-172-31-12-150-RHEL6 ebizzy-0.3]$ sudo perf stat ./ebizzy -S 10
12,409 records/s
real 10.00 s
user 7.37 s
sys 341.22 s

Performance counter stats for './ebizzy -S 10':

     361458.371052      task-clock (msec)         #   35.880 CPUs utilized
            10,343      context-switches          #    0.029 K/sec
             2,582      cpu-migrations            #    0.007 K/sec
         1,418,204      page-faults               #    0.004 M/sec

      10.074085097 seconds time elapsed

RHEL6 Flame Graph Output
www.brendangregg.com/flamegraphs.html

On RHEL7
[ec2-user@ip-172-31-7-22-RHEL7 ~]$ sudo perf stat ./ebizzy-0.3/ebizzy -S 10
425,143 records/s
real 10.00 s
user 397.28 s
sys   0.18 s

Performance counter stats for './ebizzy-0.3/ebizzy -S 10':

     397515.862535      task-clock (msec)         #   39.681 CPUs utilized
            25,256      context-switches          #    0.064 K/sec
             2,201      cpu-migrations            #    0.006 K/sec
            14,109      page-faults               #    0.035 K/sec

      10.017856000 seconds time elapsed
Up from 12,400 records/s!
Down from 1,418,204!

Hugepages
§  Disable Transparent Hugepages
# echo never > /sys/kernel/mm/transparent_hugepage/enabled
# echo never > /sys/kernel/mm/transparent_hugepage/defrag
§  Use Explicit Huge Pages
$ sudo mkdir /dev/hugetlbfs
$ sudo mount -t hugetlbfs none /dev/hugetlbfs
$ sudo sysctl -w vm.nr_hugepages=10000
$ HUGETLB_MORECORE=yes LD_PRELOAD=libhugetlbfs.so numactl --cpunodebind=0
--membind=0 /path/to/application
https://lwn.net/Articles/375096/

Hardware
Split Driver Model
Driver Domain Guest Domain
VMM
Frontend
driver
Backend
driver
Device
Driver
Physical CPU
Physical
Memory
Storage
Device
Virtual CPU
Virtual
Memory
CPU
Scheduling
Sockets
Application

Granting in pre-3.8.0 Kernels
§  Requires “grant mapping” prior to 3.8.0
§  Grant mappings are expensive operations due to TLB flushes
SSD
Inter domain I/O:
(1)  Grant memory
(2)  Write to ring buffer
(3)  Signal event
(4)  Read ring buffer
(5)  Map grants
(6)  Read or write grants
(7)  Unmap grants
read(fd, buffer,…)
I/O domain Instance
https://blog.xenproject.org/2012/11/23/improving-block-protocol-scalability-with-persistent-grants/

Persistent granting in 3.8.0+ Kernels
§  Grant mappings are set up in a pool one time
§  Data is copied in and out of the grant pool
SSD
read(fd, buffer…)
I/O domain Instance
Grant pool
Copy to
and from
grant pool

Validating Persistent Grants
[ec2-user@ip-172-31-4-129 ~]$ dmesg | egrep -i 'blkfront'
Blkfront and the Xen platform PCI driver have been compiled for this kernel: unplug emulated
disks.
blkfront: xvda: barrier or flush: disabled; persistent grants: enabled; indirect descriptors: enabled;
blkfront: xvdb: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled;
blkfront: xvdc: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled;
blkfront: xvdd: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled;
blkfront: xvde: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled;
blkfront: xvdf: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled;
blkfront: xvdg: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled;
blkfront: xvdh: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled;
blkfront: xvdi: flush diskcache: enabled; persistent grants: enabled; indirect descriptors: enabled;

2009 – Longer ago than you think
§  Avatar was the top movie in the theaters
§  Facebook overtook MySpace in active users
§  President Obama was sworn into office
§  The 2.6.32 Linux kernel was released
Tip: Use 3.10+ kernel
§  Amazon Linux 2013.09 or later
§  Ubuntu 14.04 or later
§  RHEL/Centos 7 or later
§  Etc.

Device Pass Through: Enhanced Networking
§  SR-IOV eliminates need for driver domain
§  Physical network device exposes virtual function to instance
§  Requires a specialized driver, which means:
§  Your instance OS needs to know about it
§  EC2 needs to be told your instance can use it
More information in our previous “Deep Dive VPC” webinar
https://www.youtube.com/watch?v=hUw4ehDswWo

Hardware
After Enhanced Networking
Driver Domain Guest Domain
VMM
NIC
Driver
Physical CPU
Physical
Memory
SR-IOV Network
Device
Virtual CPU
Virtual
Memory
CPU
Scheduling
Sockets
Application

Elastic Network Adapter
§  Next Generation of Enhanced Networking
§  Hardware Checksums
§  Multi-Queue Support
§  Receive Side Steering
§  20Gbps in a Placement Group
§  New Open Source Amazon Network Driver
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/enhanced-networking-ena.html
https://github.com/amzn/amzn-drivers

Network Performance
§  Use placement groups when you need high and consistent instance
to instance bandwidth
§  20 Gigabit & 10 Gigabit
§  Measured one-way, double that for bi-directional (full duplex)
§  High, Moderate, Low – A function of the instance size and EBS
optimization
§  Not all created equal – Test with iperf if it’s important!
§  All traffic limited to 5 Gb/s when exiting EC2

EBS Performance
§  Instance size affects
throughput
§  Match your volume size and
type to your instance
§  Use EBS optimization if EBS
performance is important
https://docs.aws.amazon.com/AWSEC2/latest/UserGuide/ebs-ec2-config.html

§  Choose HVM AMIs
§  Timekeeping: use TSC
§  C state and P state controls
§  Monitor T2 CPU credits
§  Use a modern Linux OS
§  NUMA balancing
§  Persistent grants for I/O performance
§  Enhanced networking
§  Profile your application!
Summary: Getting the Most Out of EC2 Instances

AWS User Groups
Lille
Paris
Rennes
Nantes
Bordeaux
Lyon
Montpellier
Toulouse
Côte d’Azur (new!)
facebook.com/groups/AWSFrance/
@aws_actus

https://aws.amazon.com/fr/events/webinaires/
Chaîne “Amazon Web Services France” sur YouTube
https://www.youtube.com/channel/UCDE2Dt16Asi-RiR_GNe9scA

Thank you!
Julien Simon
Principal Technical Evangelist, AWS
julsimon@amazon.fr
@julsimon

Deep Dive on Amazon EC2 Instances (March 2017)

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