Perf with the Linux Kernel. Copyright Kevin Dankwardt

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1 Perf with the Linux Kernel

2 perf commands annotate annotate source code with profile info kmem kernel memory profiling kvm profile guests list list kinds of events lock analyze lock events record save profile data to a file report display profile report stat gather data while running a command timechart visualize system behavior top system profiling

3 perf list ~/perf-stuff$ perf list grep Hardware cpu-cycles OR cycles instructions cache-references cache-misses branch-instructions OR branches branch-misses bus-cycles stalled-cycles-frontend OR idle-cycles-frontend ref-cycles Much more available if run as root.

4 perf stat User space example: ~/perf-stuff$ perf stat -e instructions date Wed Feb 18 21:49:03 PST 2015 Performance counter stats for 'date': 669,408 instructions seconds time elapsed Subsequent runs gave: 668,858 instructions, seconds time elapsed 667,037 instructions, seconds time elapsed

5 perf list/stat kernel sudo perf list perf calls perf_event_open(2) kernel/events/core.c sudo perf stat -e net:netif_rx wget (24MB) Performance counter stats for 'wget 2 net:netif_rx seconds time elapsed For stat -e net:netif_receive_skb 3,828 net:netif_receive_skb seconds time elapsed int netif_receive_skb(struct sk_buff *skb) { trace_netif_receive_skb_entry(skb); return netif_receive_skb_internal(skb); }

6 top run perf top with sudo perf_event_paranoid is not mentioned in./documentation defined in kernel/sysctl.c depends on CONFIG_PERF_EVENTS

7 timechart sudo perf timechart record find /usr -name core >&/dev/null sudo perf timechar display output.svg

8 report sudo perf record wget sudo perf report

9 lock sudo perf lock record wget tracepoint lock:lock_acquire is not enabled. Are CONFIG_LOCKDEP and CONFIG_LOCK_STAT enabled? under kernel hacking

10 perf kvm Perf uses CPU performance counters These need to be virtualized to properly account for performance in a Guest VM perf kvm [--host] [--guest] [--guestmount=<path> [--guestkallsyms=<path> --guestmodules=<path> --guestvmlinux=<path>]] {top record report diff buildid-list} perf kvm [--host] [--guest] [--guestkallsyms=<path> --guestmodules=<path> --guestvmlinux=<path>] {top record report diff buildid-list} Copyright 2013 K Computing

11 Virtualization Overhead VM layer overhead, Linux guest: CPU and Memory: 14.36% Network I/O: 24.46% Disk I/O: 8.84% Disk latency for reading: 2.41 times slower Micro-operations execution time: times slower Reported by: Redhat reports 85% efficiency in VM's (RHEL6 Virtualization Getting Started Guide) Copyright 2013 K Computing

kmem sudo perf kmem record wget http://tahoot.com/cs172a-lecture7.

12 kmem sudo perf kmem record wget you may lose events... Warning: Processed events and lost 10 chunks! Check IO/CPU overload!

13 kmem events sudo perf record -g -e kmem:mm_page_alloc -c 1 wget

14 annotate sudo perf annotate -l -P

15 annotate in kernel

16 report of looper with dup2()

Profiling: Understand Your Application

Profiling: Understand Your Application Michal Merta michal.merta@vsb.cz 1st of March 2018 Agenda Hardware events based sampling Some fundamental bottlenecks Overview of profiling tools perf tools Intel