Re: [LTP] [TESTING] x86: implement prctl PR_GET_TSC and PR_SET_TSC in 2.6.26

Re: [LTP] [TESTING] x86: implement prctl PR_GET_TSC and PR_SET_TSC in 2.6.26

[Subrata Modak]

Hi Erik,

On Thu, 2008-09-04 at 18:44 +0530, Subrata Modak wrote:
> Hi Erik,
> 
> On Mon, 2008-09-01 at 19:36 +0200, Erik Bosman wrote:
> > Hi Subrata,
> > 
> > Sorry for my late reaction. I'm busy working on my Master thesis right
> > now.

I would disturb you for a brief period once again.

> > 
> > On Tue, 26 Aug 2008, Subrata Modak wrote:
> > 
> > > Hi Erik,
> > >
> > > Would you kindly let us know how you tested prctl PR_GET_TSC and
> > > PR_SET_TSC, which is added in 2.6.26. Did you write/develop an automated
> > > test case(s) of your own. Let us know if you would like the same to
> > > share with LTP under GPLv2.
> > >
> > 
> > One of my patches added three tests to the Documentation/prctl, so you can
> > find them there from 2.6.26 on. They are not automated but it is not hard
> > to change that. I would recommend using disable-tsc-on-off-stress-test.c.
> 
> Thank you very much. I would look into them surely, and see how i can
> integrate them inside LTP.

I have run those tests on i686, x86_64 & ppc64 running 2.6.26 kernel.
And here are my observations:

1) Built and ran perfectly on X86_64:

# uname -a
Linux 2.6.26-autokern1 #1 SMP PREEMPT Fri Sep 5 09:40:31 UTC 2008 x86_64
GNU/Linux

# ./disable-tsc-test               
rdtsc() == 9766811077875
prctl(PR_GET_TSC, &tsc_val); tsc_val == PR_TSC_ENABLE
rdtsc() == 9766811184102
prctl(PR_SET_TSC, PR_TSC_ENABLE)
rdtsc() == 9766811200743
prctl(PR_SET_TSC, PR_TSC_SIGSEGV)
rdtsc() == [ SIG_SEGV ]
prctl(PR_GET_TSC, &tsc_val); tsc_val == PR_TSC_SIGSEGV
prctl(PR_SET_TSC, PR_TSC_ENABLE)
rdtsc() == 9766811246535
# echo $?
0

# ./disable-tsc-on-off-stress-test 
[No further output means we're allright]
# echo $?
0

# ./disable-tsc-ctxt-sw-stress-test 
[No further output means we're allright]
# echo $?
0



2) Built fine on i686, but disable-tsc-on-off-stress-test failed:

# uname -a
Linux 2.6.26-autokern1 #1 SMP Fri Sep 5 09:49:37 UTC 2008 i686 GNU/Linux

# ./disable-tsc-test 
rdtsc() == 4098191459558
prctl(PR_GET_TSC, &tsc_val); tsc_val == PR_TSC_ENABLE
rdtsc() == 4098192032718
prctl(PR_SET_TSC, PR_TSC_ENABLE)
rdtsc() == 4098192209502
prctl(PR_SET_TSC, PR_TSC_SIGSEGV)
rdtsc() == [ SIG_SEGV ]
prctl(PR_GET_TSC, &tsc_val); tsc_val == PR_TSC_SIGSEGV
prctl(PR_SET_TSC, PR_TSC_ENABLE)
rdtsc() == 4098192880534
# echo $?
0

# ./disable-tsc-on-off-stress-test 
Floating point exception
# echo $?
136

# ./disable-tsc-ctxt-sw-stress-test 
[No further output means we're allright]
# echo $?
0


3) Build failure on ppc64 with a POWER6 cpu:

# uname -a
Linux 2.6.26-autokern1 #1 SMP Fri Sep 5 05:41:12 EDT 2008 ppc64 ppc64
ppc64 GNU/Linux

# make
cc     disable-tsc-ctxt-sw-stress-test.c   -o
disable-tsc-ctxt-sw-stress-test
disable-tsc-ctxt-sw-stress-test.c: In function ‘rdtsc’:
disable-tsc-ctxt-sw-stress-test.c:33: error: impossible constraint in
‘asm’
make: *** [disable-tsc-ctxt-sw-stress-test] Error 1

# gcc --version
gcc (GCC) 4.1.2 20071124 (Red Hat 4.1.2-42)
Copyright (C) 2006 Free Software Foundation, Inc.



Can you kindly help us fix the:
1) Floating point exception for disable-tsc-on-off-stress-test, running
2.6.26 on i686,
2) build failure issue(s) with ppc64.

I also see the following issue(s) when i run it on i386 machine running
kernel less than 2.6.26:

$ uname -a
Linux 2.6.18-92.el5 #1 SMP Tue Apr 29 13:16:12 EDT 2008 i686 i686 i386
GNU/Linux

$ ./disable-tsc-test 
rdtsc() == 34367216958620
prctl(PR_GET_TSC, &tsc_val); prctl: Invalid argument
tsc_val == [not set]
rdtsc() == 34367217591252
prctl(PR_SET_TSC, PR_TSC_ENABLE)
prctl: Invalid argument
rdtsc() == 34367217645449
prctl(PR_SET_TSC, PR_TSC_SIGSEGV)
prctl: Invalid argument
rdtsc() == 34367217698450
$ echo $?
0

$ ./disable-tsc-ctxt-sw-stress-test 
[No further output means we're allright]
prctl: Invalid argument
prctl: Invalid argument
..............
..............
prctl: Invalid argument
$ echo $?
0

$ ./disable-tsc-ctxt-sw-stress-test 
[No further output means we're allright]
prctl: Invalid argument
prctl: Invalid argument
..............
..............
prctl: Invalid argument
$ echo $?
0

Should it not fail on any kernel(s) below 2.6.26 ? It shows pass for all
the tests. And also lots of lines like:

prctl: Invalid argument

is printed, which in ideal situation should not be printed at all. What
do you think ?

Regards--
Subrata

> 
> > 
> > Is it a problem if the test causes a very high load?
> 
> No, there is no such problem. But we will run it separately rather than
> with default run. Normally, we run the stress tests separately from the
> normal functional tests.
> 
> Regards--
> Subrata
> 
> > 
> > > We already have the prctl() test cases in LTP and probably with this
> > > addition, we need to add some more tests to the existing scenario. Would
> > > you review the existing ones too:
> > >
> > > http://ltp.cvs.sourceforge.net/ltp/ltp/testcases/kernel/syscalls/prctl/,
> > 
> > Prctl is by definition a very diverse syscall, I am not an expert on
> > all prctl calls. I don't think I can help you with many of them (as I
> > don't have the hardware, ) and as I said, I'm rather busy finishing my
> > master thesis.
> > 
> > Regards,
> > Erik
> 
> 
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Re: [LTP] [TESTING] x86: implement prctl PR_GET_TSC and PR_SET_TSC in 2.6.26

[Erik Bosman]

On Fri, 5 Sep 2008, Subrata Modak wrote:
>
> 2) Built fine on i686, but disable-tsc-on-off-stress-test failed:
>
> # uname -a
> Linux 2.6.26-autokern1 #1 SMP Fri Sep 5 09:49:37 UTC 2008 i686 GNU/Linux
>
> # ./disable-tsc-test
> rdtsc() == 4098191459558
> prctl(PR_GET_TSC, &tsc_val); tsc_val == PR_TSC_ENABLE
> rdtsc() == 4098192032718
> prctl(PR_SET_TSC, PR_TSC_ENABLE)
> rdtsc() == 4098192209502
> prctl(PR_SET_TSC, PR_TSC_SIGSEGV)
> rdtsc() == [ SIG_SEGV ]
> prctl(PR_GET_TSC, &tsc_val); tsc_val == PR_TSC_SIGSEGV
> prctl(PR_SET_TSC, PR_TSC_ENABLE)
> rdtsc() == 4098192880534
> # echo $?
> 0
>
> # ./disable-tsc-on-off-stress-test
> Floating point exception
> # echo $?
> 136

I'm a bit puzzled by this, since I don't use any floats
in my test (or even integer division.)

Another strange thing is that it is the parent process getting
the signal, while the parent doesn't do anything but forking
and waiting.

If the bug was in the kernel (for example sending a SIGFPE instead
of a SIGSEGV,) the signal would be expected to go to the child process
doing the actual testing (I know, bugs are bugs, but my patches were
not that invasive.)

Does it fail every time? Does it fail immediately? Can you use gdb
to locate where it happens?

I cannot reproduce this error using gcc 4.2.3.
Valgrind doesn't give me any errors except uninitialized (and in
this case unused) prctl arguments.
Could it be a optimization bug?

>
> # ./disable-tsc-ctxt-sw-stress-test
> [No further output means we're allright]
> # echo $?
> 0
>
>
> 3) Build failure on ppc64 with a POWER6 cpu:
>

The test uses the intel RDTSC instruction
and PR_SET_TSC/PR_GET_TSC is currently only
implemented on x86. So it is of little use to
try to compile this test on other platforms.

>
> Can you kindly help us fix the:
> 1) Floating point exception for disable-tsc-on-off-stress-test, running
> 2.6.26 on i686,
> 2) build failure issue(s) with ppc64.
>
> I also see the following issue(s) when i run it on i386 machine running
> kernel less than 2.6.26:
>

...

> $ ./disable-tsc-ctxt-sw-stress-test
> [No further output means we're allright]
> prctl: Invalid argument
> prctl: Invalid argument
> ..............
> ..............
> prctl: Invalid argument
> $ echo $?
> 0
>
> $ ./disable-tsc-ctxt-sw-stress-test
> [No further output means we're allright]
> prctl: Invalid argument
> prctl: Invalid argument
> ..............
> ..............
> prctl: Invalid argument
> $ echo $?
> 0
>
> Should it not fail on any kernel(s) below 2.6.26 ? It shows pass for all
> the tests. And also lots of lines like:
>
> prctl: Invalid argument
>
> is printed, which in ideal situation should not be printed at all. What
> do you think ?
>
> Regards--
> Subrata
>

The current test wasn't written to be integrated into an automated testing
framework and only uses stderr output for error reporting. To integrate
the test into a framework, just test whether all children terminate using
SIGALRM (which means success.)

Regards,
Erik Bosman