20-30% Performance Hit from the Spectre Bug Fix on Ubuntu

In this blog post, we’ll look at the performance hit from the Spectre bug fix on Ubuntu.

Recently we measured the performance penalty from the Meltdown fix on Ubuntu servers. It turned out to be negligible.

Today, Ubuntu made a Spectre bug fix on Ubuntu available, shipped in kernel 4.4.0-112. As with the Meltdown fix, we measured the effect of this update. Unfortunately, we observed a major performance penalty on MySQL workloads with this new kernel.

Our benchmark used the following:

System:

• CPU:

  • 2 x Intel(R) Xeon(R) CPU E5-2680 v3 @ 2.50GHz (Codename Haswell)
  • /proc/cpuinfo has 48 entries

• Server

  • Supermicro Motherboard X10DRI

• Storage

  • NVMi Intel DC 36000

• Ubuntu 16.04

  • no-fix – kernel 4.4.0-104-generic
  • fix (now GA) – kernel 4.4.0-112-generic

With the fix, the Spectre and Meltdown mitigation detection tool v0.27 reports following:

Workload:

• sysbench 1.0.11 oltp_read_only and oltp_point_select
• 32 tables, 10mln rows each
• datasize ~73GB

Server:

• Percona-Server-5.7.20-19-Linux.x86_64 binary distribution
• config https://github.com/Percona-Lab-results/201701-meltdown-OLTP-ro/blob/master/my.cnf

Sysbench script:

• https://github.com/Percona-Lab-results/201701-meltdown-OLTP-ro/blob/master/run_sysbench.sh

The results

The results are in transactions per sec (more is better).

In memory (buffer pool 100G)

Connection via TCP

Buffer pool 50G

Connection via TCP

Buffer pool 25G

connection via TCP

 

We can see that in CPU-bound workloads the overhead is 20-25%, reaching up to 30% in point select queries. In IO-bound (25G buffer pool) workloads, the observed overhead is 15-20%.

This is a major performance hit, and you should consider it carefully before upgrading to the new kernel.

One hope that is retpoline kernels will have much less impact.