[PATCH] D29954: [PGO] Suspend SIGKILL for PR_SET_PDEATHSIG in profile-write

[Rong Xu via llvm-commits]

this is basically the simple tested I described.

but the child process cannot sleep, as if it sleeps, it will be killed when
the parent process exit. This happens before getting into the profile
run-time. There would be no chance of merge.

it's hard to control the timing. I can only test that no 0-sized profile
will be created.
I cannot guarantee merge will happen.

On Wed, Feb 15, 2017 at 10:03 AM, Xinliang David Li <davidxl at google.com>
wrote:

> You can write a test that has high chance of failure when this patch is
> not applied. This can be done by let child process to sleep a few ms before
> existing. The period of waiting can be controlled by a command line
> argument.
>
> Things to test:
>
> 1) make sure the profile data is not zero sized
> 2) make sure the merged profile from parent and child is created (using
> llvm-profdata to dump)
>
> 3) repeat step 1) and 2) with different waiting parameters (e.g, 3
> different cases).
>
> David
>
> On Wed, Feb 15, 2017 at 9:55 AM, Rong Xu <xur at google.com> wrote:
>
>> It's not easy to write a test case for this. We need the extended period
>> of profile write to expose the faulty behavior. This is not easy for small
>> test programs.
>> I can register another atexit function that opens and locks the profile
>> to mimic this.
>> The flow is like:
>> main process:  __llvm_profile_write_file, open_profile, lock_profile,
>> close_profile, _exit
>> child process:    sleep
>>  __llvm_profile_write
>>
>> But this is not really testing the code directly.
>> Another thing is since merge is only enabled with %m specifier, i need to
>> get the string expansion for %m, or I need to read the directory to find
>> the profile. This is quite cumbersome.
>>
>> Or a simple version is just a test that using small profile and let the
>> race happen.
>> There are two outcomes: (1) if the main process exits before the child
>> process voiding the sigkill, we have the profile for the main process only.
>> (2) if the child process get time to void sigkill, we get merged profile.
>> The check would assert that 0-size profile should not happen.
>>
>> Do you have better idea?
>>
>>
>> On Wed, Feb 15, 2017 at 9:38 AM, Rong Xu <xur at google.com> wrote:
>>
>>>
>>>
>>> On Tue, Feb 14, 2017 at 1:05 PM, David Li via Phabricator <
>>> reviews at reviews.llvm.org> wrote:
>>>
>>>> davidxl added a comment.
>>>>
>>>> Can you create a test case? It can be put under the Linux subdir.
>>>>
>>>>
>>>> https://reviews.llvm.org/D29954
>>>>
>>>>
>>>>
>>>>
>>>
>>
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: <http://lists.llvm.org/pipermail/llvm-commits/attachments/20170215/4a18d0f4/attachment.html>