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Tuning for Zero Packet Loss in Red Hat OpenStack Platform – Part 3

In Part 1 of this series Federico Iezzi, EMEA Cloud Architect with Red Hat covered the architecture and planning requirements to begin the journey into achieving zero packet loss in Red Hat OpenStack Platform 10 for NFV deployments. In Part 2 he went into the details around the specific tuning and parameters required. Now, in Part 3, Federico concludes the series with an example of how all this planning and tuning comes together!

opwithtoolsinside

Putting it all together …

So, what happens when you use the cpu tuning features?

Well, it depends on the hardware choice of course. But to see some examples we can use Linux perf events to see what is going on. Let’s look at two examples.

Virtual Machine

On a KVM VM, you will have the ideal results because you don’t have all of the interrupts from the real hardware:

$ perf record -g -C 1 -- sleep 2h
$ perf report --stdio -n
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 100  of event 'cpu-clock'
# Event count (approx.): 25000000
#
# Children      Self  Command  Shared Object      Symbol               
# ........  ........  .......  .................  .....................
#
   100.00%     0.00%  swapper  [kernel.kallsyms]  [k] default_idle
            |
            ---default_idle
               native_safe_halt
   100.00%     0.00%  swapper  [kernel.kallsyms]  [k] arch_cpu_idle
            |
            ---arch_cpu_idle
               default_idle
               native_safe_halt
   100.00%     0.00%  swapper  [kernel.kallsyms]  [k] cpu_startup_entry
            |
            ---cpu_startup_entry
               arch_cpu_idle
               default_idle
               native_safe_halt
   100.00%   100.00%  swapper  [kernel.kallsyms]  [k] native_safe_halt
            |
            ---start_secondary
               cpu_startup_entry
               arch_cpu_idle
               default_idle
               native_safe_halt
   100.00%     0.00%  swapper  [kernel.kallsyms]  [k] start_secondary
            |
            ---start_secondary
               cpu_startup_entry
               arch_cpu_idle
               default_idle
               native_safe_halt

Physical Machine

On physical hardware, it’s quite different. The best results involved backlighting a bunch of ipmi and watchdog kernel modules:

$ modprobe -r iTCO_wdt iTCO_vendor_support
$ modprobe -r i2c_i801
$ modprobe -r ipmi_si ipmi_ssif ipmi_msghandler

Note: If you have a different watchdog than the example above, (iTCO is for Supermicro motherboards), check out the kernel modules folder where you can find the whole list: /lib/modules/*/kernel/drivers/watchdog/

Here’s the perf command and output for physical:

$ perf record -F 99 -g -C 2 -- sleep 2h
$ perf report --stdio -n
# To display the perf.data header info, please use --header/--header-only options.
#
#
# Total Lost Samples: 0
#
# Samples: 4  of event 'cycles:ppp'
# Event count (approx.): 255373
#
# Children      Self       Samples  Command  Shared Object      Symbol                                        
# ........  ........  ............  .......  .................  ..............................................
#
    99.83%     0.00%             0  swapper  [kernel.kallsyms]  [k] generic_smp_call_function_single_interrupt
            |
            ---generic_smp_call_function_single_interrupt
               |          
                --99.83%--nmi_restore
    99.83%     0.00%             0  swapper  [kernel.kallsyms]  [k] smp_call_function_single_interrupt
            |
            ---smp_call_function_single_interrupt
               generic_smp_call_function_single_interrupt
               |          
                --99.83%--nmi_restore
    99.83%     0.00%             0  swapper  [kernel.kallsyms]  [k] call_function_single_interrupt
            |
            ---call_function_single_interrupt
               smp_call_function_single_interrupt
               generic_smp_call_function_single_interrupt
               |          
                --99.83%--nmi_restore
    99.83%     0.00%             0  swapper  [kernel.kallsyms]  [k] cpuidle_idle_call
            |
            ---cpuidle_idle_call
               call_function_single_interrupt
               smp_call_function_single_interrupt
               generic_smp_call_function_single_interrupt
               |          
                --99.83%--nmi_restore
    99.83%     0.00%             0  swapper  [kernel.kallsyms]  [k] arch_cpu_idle
            |
            ---arch_cpu_idle
               cpuidle_idle_call
               call_function_single_interrupt
               smp_call_function_single_interrupt
               generic_smp_call_function_single_interrupt
               |          
                --99.83%--nmi_restore

Using mpstat, and excluding the hardware interrupts, the results are as follows:

Please note: one CPU core per socket has been excluded – in this case using two Xeon E5-2640 V4.

$ mpstat -P 1,2,3,4,5,6,7,8,9,11,12,13,14,15,16,17,18,19,21,22,23,24,25,26,27,28,29,31,32,32,34,35,36,37,38,39 3600
Linux 3.10.0-514.16.1.el7.x86_64 (ws1.localdomain)      04/20/2017      _x86_64_     (40 CPU)

03:05:10 PM  CPU    %usr   %nice    %sys %iowait    %irq   %soft  %steal  %guest  %gnice   %idle
Average:       1    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:       2    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:       3    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:       4    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:       5    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:       6    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:       7    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:       8    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:       9    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      11    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      12    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      13    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      14    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      15    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      16    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      17    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      18    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      19    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      21    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      22    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      23    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      24    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      25    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      26    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      27    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      28    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      29    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      31    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      32    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      34    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      35    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      36    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      37    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      38    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00
Average:      39    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00    0.00  100.00

Cool, right? Want to know more about Linux perf events? Check out the following links:

Zero Packet Loss, achieved …

As you can see, using tuned and the cpu-partitioning profile is exceptional in that it exposes a lot of deep Linux tuning which usually only a few people know about.

IMG_0786

And with a combination of tuning, service settings, and plenty of  interrupt isolations (over 50% of the total settings are about interrupt isolations!) things really start to fly.

Finally, once you make sure PMD threads and VNF vCPUs do not get interrupted by other threads allowing for proper CPU core allocation, the zero packet loss game is achieved.

Of course, there are other considerations such as the hardware chosen, the VNF quality, and the number of PMD threads, but, generally speaking, those are the main requirements.

Further Reading …

Red Hat Enterprise Linux Performance Tuning Guide
Network Functions Virtualization Configuration Guide (Red Hat OpenStack Platform 10)


Check out the Red Hat Services Webinar Don’t fail at scale: How to plan, build, and operate a successful OpenStack cloud today! 


The “Operationalizing OpenStack” series features real-world tips, advice and experiences from experts running and deploying OpenStack.


Source: Redhat

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