On 2015/9/7 20:51, Wang Nan wrote:
[SNIP]
Although theoretically CPU_TOPOLOGY feature should always be selected by
'perf record', I did generate a perf.data without that feature. It has
header like this:
# perf report -i ./bad.perf.data --header-only
# ========
# captured on: Thu Jan 8 09:30:15 2009
# hostname : localhost
# os release : 3.10.49-gd672fc4
# perf version : 4.2.gc9df
# arch : aarch64
# nrcpus online : 8
# nrcpus avail : 8
# total memory : 1850768 kB
# cmdline : /system/bin/perf record -e sync:sync_timeline -e
kgsl:kgsl_register_event -g -a sleep 5
# event : name = sync:sync_timeline, , id = { 1107, 1108, 1109, 1110, 1111,
1112 }, type = 2, size = 112, config = 0x3e7, { sample_period, sample_freq } =
1, sample_type = IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW, read_format = ID,
disabled = 1, inherit = 1, mmap = 1, comm = 1, task = 1, sample_id_all = 1,
exclude_guest = 1, mmap2 = 1, comm_exec = 1
# event : name = kgsl:kgsl_register_event, , id = { 1113, 1114, 1115, 1116,
1117, 1118 }, type = 2, size = 112, config = 0x350, { sample_period,
sample_freq } = 1, sample_type = IP|TID|TIME|CALLCHAIN|ID|CPU|PERIOD|RAW,
read_format = ID, disabled = 1, inherit = 1, sample_id_all = 1, exclude_guest =
1
# pmu mappings: cpu = 4, software = 1, tracepoint = 2
# ========
#
It should be:
# ========
# captured on: Thu Jan 8 11:26:41 2009
...
# HEADER_CPU_TOPOLOGY info available, use -I to display
# pmu mappings: cpu = 4, software = 1, tracepoint = 2
# ========
However, bad perf.data appears randomly. I can't stably reproduce it, so I
guess there might have another invalid memory accessing.
I found the problem.
perf relies on build_cpu_topology() to fetch CPU_TOPOLOGY from sysfs. It
depend on
the existance of
/sys/devices/system/cpu/cpu%d/topology/core_siblings_list
However, CPU can be canceled by hotcpu subsystem. After that the
directory of
/sys/devices/system/cpu/cpu%d/topology is gone, which causes perf's
write_cpu_topology() --> uild_cpu_topology() to fail, result in the
above perf.data.
So I think my patch is required.
Thank you.
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