diff options
author | David S. Miller <davem@davemloft.net> | 2016-02-20 00:21:44 -0500 |
---|---|---|
committer | David S. Miller <davem@davemloft.net> | 2016-02-20 00:21:44 -0500 |
commit | 80c804bfc487c6df783c258b9034b9d81c34f7a0 (patch) | |
tree | ec8f20a73795ff16ed02887eb72870eeeee186a8 /net/8021q/vlan_dev.c | |
parent | 6b83d28a55a891a9d70fc61ccb1c138e47dcbe74 (diff) | |
parent | a6ffe7b9df6228d11c5689914eceb488bc4e38df (diff) | |
download | linux-stable-80c804bfc487c6df783c258b9034b9d81c34f7a0.tar.gz linux-stable-80c804bfc487c6df783c258b9034b9d81c34f7a0.tar.bz2 linux-stable-80c804bfc487c6df783c258b9034b9d81c34f7a0.zip |
Merge branch 'bpf-get-stackid'
Alexei Starovoitov says:
====================
bpf_get_stackid() and stack_trace map
This patch set introduces new map type to store stack traces and
corresponding bpf_get_stackid() helper.
BPF programs already can walk the stack via unrolled loop
of bpf_probe_read()s which is ok for simple analysis, but it's
not efficient and limited to <30 frames after that the programs
don't fit into MAX_BPF_STACK. With bpf_get_stackid() helper
the programs can collect up to PERF_MAX_STACK_DEPTH both
user and kernel frames.
Using stack traces as a key in a map turned out to be very useful
for generating flame graphs, off-cpu graphs, waker and chain graphs.
Patch 3 is a simplified version of 'offwaketime' tool which is
described in detail here:
http://brendangregg.com/blog/2016-02-01/linux-wakeup-offwake-profiling.html
Earlier version of this patch were using save_stack_trace() helper,
but 'unreliable' frames add to much noise and two equiavlent
stack traces produce different 'stackid's.
Using lockdep style of storing frames with MAX_STACK_TRACE_ENTRIES is
great for lockdep, but not acceptable for bpf, since the stack_trace
map needs to be freed when user Ctrl-C the tool.
The ftrace style with per_cpu(struct ftrace_stack) is great, but it's
tightly coupled with ftrace ring buffer and has the same 'unreliable'
noise. perf_event's perf_callchain() mechanism is also very efficient
and it only needed minor generalization which is done in patch 1
to be used by bpf stack_trace maps.
Peter, please take a look at patch 1.
If you're ok with it, I'd like to take the whole set via net-next.
Patch 1 - generalization of perf_callchain()
Patch 2 - stack_trace map done as lock-less hashtable without link list
to avoid spinlock on insertion which is critical path when
bpf_get_stackid() helper is called for every task switch event
Patch 3 - offwaketime example
After the patch the 'perf report' for artificial 'sched_bench'
benchmark that doing pthread_cond_wait/signal and 'offwaketime'
example is running in the background:
16.35% swapper [kernel.vmlinux] [k] intel_idle
2.18% sched_bench [kernel.vmlinux] [k] __switch_to
2.18% sched_bench libpthread-2.12.so [.] pthread_cond_signal@@GLIBC_2.3.2
1.72% sched_bench libpthread-2.12.so [.] pthread_mutex_unlock
1.53% sched_bench [kernel.vmlinux] [k] bpf_get_stackid
1.44% sched_bench [kernel.vmlinux] [k] entry_SYSCALL_64
1.39% sched_bench [kernel.vmlinux] [k] __call_rcu.constprop.73
1.13% sched_bench libpthread-2.12.so [.] pthread_mutex_lock
1.07% sched_bench libpthread-2.12.so [.] pthread_cond_wait@@GLIBC_2.3.2
1.07% sched_bench [kernel.vmlinux] [k] hash_futex
1.05% sched_bench [kernel.vmlinux] [k] do_futex
1.05% sched_bench [kernel.vmlinux] [k] get_futex_key_refs.isra.13
The hotest part of bpf_get_stackid() is inlined jhash2, so we may consider
using some faster hash in the future, but it's good enough for now.
====================
Signed-off-by: David S. Miller <davem@davemloft.net>
Diffstat (limited to 'net/8021q/vlan_dev.c')
0 files changed, 0 insertions, 0 deletions