runtime/trace: time stamps out of order

[tv42]

The RDTSCP event ordering logic talked about in #10512 and #15102 (tricky palindrome bug numbers) doesn't seem to be working, at all.

1. What version of Go are you using (go version)?

go version go1.7 linux/amd64

1. What operating system and processor architecture are you using (go env)?

GOARCH="amd64"
GOBIN=""
GOEXE=""
GOHOSTARCH="amd64"
GOHOSTOS="linux"
GOOS="linux"
GOPATH="/home/tv/go"
GORACE=""
GOROOT="/home/tv/src/go-1.7"
GOTOOLDIR="/home/tv/src/go-1.7/pkg/tool/linux_amd64"
CC="gcc"
GOGCCFLAGS="-fPIC -m64 -pthread -fmessage-length=0 -fdebug-prefix-map=/home/tv/tmp/go-build703689621=/tmp/go-build -gno-record-gcc-switches"
CXX="g++"
CGO_ENABLED="1"

/proc/cpuinfo contents:

processor   : 0
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 1820.625
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 0
cpu cores   : 6
apicid      : 0
initial apicid  : 0
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 1
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 3547.000
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 0
cpu cores   : 6
apicid      : 1
initial apicid  : 1
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 2
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 3080.625
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 1
cpu cores   : 6
apicid      : 2
initial apicid  : 2
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 3
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 3674.000
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 1
cpu cores   : 6
apicid      : 3
initial apicid  : 3
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 4
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 3337.750
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 2
cpu cores   : 6
apicid      : 4
initial apicid  : 4
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 5
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 3775.750
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 2
cpu cores   : 6
apicid      : 5
initial apicid  : 5
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 6
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 2750.875
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 3
cpu cores   : 6
apicid      : 6
initial apicid  : 6
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 7
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 3787.375
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 3
cpu cores   : 6
apicid      : 7
initial apicid  : 7
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 8
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 2576.375
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 4
cpu cores   : 6
apicid      : 8
initial apicid  : 8
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 9
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 3362.000
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 4
cpu cores   : 6
apicid      : 9
initial apicid  : 9
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 10
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 2986.375
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 5
cpu cores   : 6
apicid      : 10
initial apicid  : 10
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

processor   : 11
vendor_id   : GenuineIntel
cpu family  : 6
model       : 45
model name  : Intel(R) Core(TM) i7-3930K CPU @ 3.20GHz
stepping    : 7
microcode   : 0x710
cpu MHz     : 3744.125
cache size  : 12288 KB
physical id : 0
siblings    : 12
core id     : 5
cpu cores   : 6
apicid      : 11
initial apicid  : 11
fpu     : yes
fpu_exception   : yes
cpuid level : 13
wp      : yes
flags       : fpu vme de pse tsc msr pae mce cx8 apic sep mtrr pge mca cmov pat pse36 clflush dts acpi mmx fxsr sse sse2 ss ht tm pbe syscall nx pdpe1gb rdtscp lm constant_tsc arch_perfmon pebs bts rep_good nopl xtopology nonstop_tsc aperfmperf eagerfpu pni pclmulqdq dtes64 monitor ds_cpl vmx est tm2 ssse3 cx16 xtpr pdcm pcid dca sse4_1 sse4_2 x2apic popcnt tsc_deadline_timer aes xsave avx lahf_lm ida arat epb pln pts dtherm tpr_shadow vnmi flexpriority ept vpid xsaveopt
bugs        :
bogomips    : 6400.32
clflush size    : 64
cache_alignment : 64
address sizes   : 46 bits physical, 48 bits virtual
power management:

1. What did you do?

Imported net/http/pprof, put load on the application (webserver + wrk), fetched http://localhost:9999/debug/pprof/trace?seconds=1, ran go tool trace trace.out

1. What did you expect to see?

Web browser opening to the trace viewer.

1. What did you see instead?

2016/08/16 16:48:46 Parsing trace...
failed to parse trace: time stamps out of order

If I constrain the app to a single core with taskset, the trace viewer works.

taskset -c 1 env GOMAXPROCS=1 ./myapp

[tv42]

Oh this might be relevant, too:

Linux brute 4.2.0-38-generic #45-Ubuntu SMP Wed Jun 8 21:21:49 UTC 2016 x86_64 x86_64 x86_64 GNU/Linux

[tv42]

$ go test -v -run=TestTraceFutileWakeup runtime/trace
=== RUN   TestTraceFutileWakeup
--- SKIP: TestTraceFutileWakeup (0.03s)
    trace_test.go:67: skipping trace: time stamps out of order
PASS
ok      runtime/trace   0.034s

[rsc]

Is this running in a VM or directly on physical hardware? Looks like a laptop?

[tv42]

brute in the above is a desktop machine, bare metal.

[bradfitz]

/cc @dvyukov @hyangah -- this sounds like a dup of something I saw once before. Ring any bells?

[dvyukov]

This looks like a buggy processor/OS. @tv42 are you sure that C programs get reasonable data out of RDTSC on this machine?
We probably need a litmus test C program checked in somewhere. But we don't have it as far as I know.

[tv42]

I'm not sure why you'd call an RDTSC varying between cores/chips "buggy". I mean, this particular BIOS may even fail to synchronize TSC between the cores at boot, and it may be buggy, but the assumption of unified TSC across cores is not safe.

Invariant TSC was a feature added to the Nehalem generation Intel chips, and even then you have no guarantees that the computer doesn't actually have multiple cpus (not just multiple cores on one cpu).

You just simply can't rely on a singular RDTSC source across all possible cores, without further information that that assumption is safe. Outside of a kernel, that sounds like risky business.

http://lxr.linux.no/linux+v2.6.38/arch/x86/kernel/tsc.c#L859

[tv42]

For what it's worth, Linux properly diagnoses TSC as unreliable on this host, and uses hpet instead.

$ cat /sys/devices/system/clocksource/clocksource0/current_clocksource 
hpet

Decent summary of TSC issues (talks about hardware, also outside of virtualization):
https://git.kernel.org/pub/scm/linux/kernel/git/torvalds/linux.git/tree/Documentation/virtual/kvm/timekeeping.txt?h=v4.12-rc5