Messages in this thread | | | Date | Mon, 7 Sep 2015 21:27:26 +0800 | From | "Wangnan (F)" <> | Subject | Re: [PATCH] perf report: Fix invalid memory accessing |
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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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