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Date:   Wed, 12 Aug 2020 08:16:57 -0700
From:   Eric Dumazet <eric.dumazet@...il.com>
To:     sedat.dilek@...il.com, Eric Dumazet <edumazet@...gle.com>
Cc:     netdev@...r.kernel.org
Subject: Re: Flaw in "random32: update the net random state on interrupt and
 activity"



On 8/11/20 11:03 PM, Sedat Dilek wrote:
> [ CC netdev ]
> [ Please CC me I am not subscribed to this mailing-list ]
> 
> Hi Eric,
> 
> I have added your diffs from [0] and have some troubles to display the
> prandom_32 trace-events (I mostly followed [1]):
> 
> I did:
> 
> echo prandom_u32 >> /sys/kernel/debug/tracing/set_event
> echo traceon > /sys/kernel/debug/tracing/events/random/prandom_u32/trigger
> echo 1 > /sys/kernel/debug/tracing/events/enable
> 
> cat /sys/kernel/debug/tracing/set_event | grep prandom
> random:prandom_u32
> cat /sys/kernel/debug/tracing/events/random/prandom_u32/trigger
> traceon:unlimited
> cat /sys/kernel/debug/tracing/events/enable
> X
> 
> Following [2] and [3] I wanted to use perf:
> 
> # /home/dileks/bin/perf list | grep prandom
>   random:prandom_u32                                 [Tracepoint event]
> 
> Following the example in [4]:
> 
> # /home/dileks/bin/perf probe --add tcp_sendmsg
> # /home/dileks/bin/perf record -e probe:tcp_sendmsg -a -g -- sleep 10
> # /home/dileks/bin/perf report --stdio
> 
> That gives me a report.
> 
> Adapting:
> 
> # /home/dileks/bin/perf probe --add tcp_conn_request
> 
> # /home/dileks/bin/perf list | grep probe:
>   probe:tcp_conn_request                             [Tracepoint event]
>   probe:tcp_sendmsg                                  [Tracepoint event]
> 
> # home/dileks/bin/perf record -e probe:tcp_conn_request -a -g -- sleep 10
> 
> # /home/dileks/bin/perf report --stdio
> Error:
> The perf.data data has no samples!
> # To display the perf.data header info, please use
> --header/--header-only options.
> #
> 
> # /home/dileks/bin/perf report --stdio --header-only
> # ========
> # captured on    : Wed Aug 12 07:39:42 2020
> # header version : 1
> # data offset    : 440
> # data size      : 2123144
> # feat offset    : 2123584
> # hostname : iniza
> # os release : 5.8.1-2-amd64-llvm11-ias
> # perf version : 5.8.1
> # arch : x86_64
> # nrcpus online : 4
> # nrcpus avail : 4
> # cpudesc : Intel(R) Core(TM) i5-2467M CPU @ 1.60GHz
> # cpuid : GenuineIntel,6,42,7
> # total memory : 8046012 kB
> # cmdline : /home/dileks/bin/perf record -e probe:tcp_conn_request -a
> -g -- sleep 10
> # event : name = probe:tcp_conn_request, , id = { 304, 305, 306, 307
> }, type = 2, size = 120, config = 0x866, { sample_period, sample_freq
> } = 1, sample_type = IP|TID|TIME|CALLCHAIN|CPU|PERIO>
> # event : name = dummy:HG, , id = { 308, 309, 310, 311 }, type = 1,
> size = 120, config = 0x9, { sample_period, sample_freq } = 4000,
> sample_type = IP|TID|TIME|CALLCHAIN|CPU|PERIOD|IDENTIFIER,>
> # CPU_TOPOLOGY info available, use -I to display
> # NUMA_TOPOLOGY info available, use -I to display
> # pmu mappings: software = 1, power = 14, uprobe = 7, cpu = 4,
> cstate_core = 12, breakpoint = 5, uncore_cbox_0 = 9, tracepoint = 2,
> cstate_pkg = 13, uncore_arb = 11, kprobe = 6, i915 = 15, ms>
> # CACHE info available, use -I to display
> # time of first sample : 0.000000
> # time of last sample : 0.000000
> # sample duration :      0.000 ms
> # MEM_TOPOLOGY info available, use -I to display
> # bpf_prog_info 3: bpf_prog_6deef7357e7b4530 addr 0xffffffffc01d7834 size 66
> # bpf_prog_info 4: bpf_prog_6deef7357e7b4530 addr 0xffffffffc01df7e8 size 66
> # bpf_prog_info 5: bpf_prog_6deef7357e7b4530 addr 0xffffffffc041ca18 size 66
> # bpf_prog_info 6: bpf_prog_6deef7357e7b4530 addr 0xffffffffc041eb58 size 66
> # bpf_prog_info 7: bpf_prog_6deef7357e7b4530 addr 0xffffffffc1061dc0 size 66
> # bpf_prog_info 8: bpf_prog_6deef7357e7b4530 addr 0xffffffffc1063388 size 66
> # bpf_prog_info 12: bpf_prog_6deef7357e7b4530 addr 0xffffffffc129c244 size 66
> # bpf_prog_info 13: bpf_prog_6deef7357e7b4530 addr 0xffffffffc129e8c0 size 66
> # cpu pmu capabilities: branches=16, max_precise=2, pmu_name=sandybridge
> # missing features: BRANCH_STACK GROUP_DESC AUXTRACE STAT CLOCKID
> DIR_FORMAT COMPRESSED
> # ========
> #
> 
> In dmesg I see:
> 
> [Wed Aug 12 07:30:52 2020] Scheduler tracepoints stat_sleep,
> stat_iowait, stat_blocked and stat_runtime require the kernel
> parameter schedstats=enable or kernel.sched_schedstats=1
> 
> CONFIG_SCHEDSTATS=y is set.
> 
> # echo 1 > /proc/sys/kernel/sched_schedstats
> # cat /proc/sys/kernel/sched_schedstats
> 1
> 
> Still seeing:
> # /home/dileks/bin/perf report --stdio
> Error:
> The perf.data data has no samples!
> # To display the perf.data header info, please use
> --header/--header-only options.
> #
> 
> Do I miss to set some required Kconfigs?
> I have attached my latest kernel-config file.
> 
> So I need a helping hand how to trace prandom_u32 events in general?


perf record -a -g -e random:prandom_u32  sleep 5

Then something like

perf report --no-children

or "perf script"

> 
> How to add it as a kernel-boot-parameter (see [4])?
> 
> Any help appreciated and thanks in advance.
> 
> Thanks.
> 
> Regards,
> - Sedat -
> 
> [0] https://marc.info/?l=linux-netdev&m=159716173516111&w=2
> [1] https://www.kernel.org/doc/html/v5.8/trace/events.html
> [2] http://www.brendangregg.com/perf.html
> [3] http://www.brendangregg.com/perf.html#DynamicTracing
> [4] https://www.kernel.org/doc/html/v5.8/trace/events.html#boot-option
> 

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