[compiler-rt] r295364 - [PGO] Suspend SIGKILL for PR_SET_PDEATHSIG in profile-write
Rong Xu via llvm-commits
llvm-commits at lists.llvm.org
Fri Feb 17 09:57:32 PST 2017
Is this system very slow in file write? I think the test tries to dump the
profile while the child process still write the file.
I have a sleep(1) b/w the end of main process and profile dump. It seems
this is no enough.
Is it possible to get a temporal access to this machine?
If not, I can reduce the profile size or have a longer wait period before
profile dump.
-Rong
On Fri, Feb 17, 2017 at 5:55 AM, Diana Picus <diana.picus at linaro.org> wrote:
> Hi,
>
> This test has been failing every now and then on one of our bots:
> http://lab.llvm.org:8011/waterfall?show=clang-cmake-aarch64-42vma
> (builds 4700, 4695, 4690. 4671 etc)
>
> Any idea what the problem might be?
>
> Thanks,
> Diana
>
> On 16 February 2017 at 20:21, Rong Xu via llvm-commits
> <llvm-commits at lists.llvm.org> wrote:
> > Author: xur
> > Date: Thu Feb 16 13:21:31 2017
> > New Revision: 295364
> >
> > URL: http://llvm.org/viewvc/llvm-project?rev=295364&view=rev
> > Log:
> > [PGO] Suspend SIGKILL for PR_SET_PDEATHSIG in profile-write
> >
> > Summary:
> > We found a nondeterministic behavior when doing online profile merging
> > for multi-process applications. The application forks a sub-process and
> > sub-process sets to get SIGKILL when the parent process exits,
> >
> > The first process gets the lock, and dumps the profile. The second one
> > will mmap the file, do the merge and write out the file. Note that before
> > the merged write, we truncate the profile.
> >
> > Depending on the timing, the child process might be terminated
> > abnormally when the parent exits first. If this happens:
> > (1) before the truncation, we will get the profile for the main process
> > (2) after the truncation, and before write-out the profile, we will get
> > 0 size profile.
> > (3) after the merged write, we get merged profile.
> >
> > This patch temporarily suspend the SIGKILL for PR_SET_PDEATHSIG
> > before profile-write and restore it after the write.
> >
> > This patch only applies to Linux system.
> >
> > Reviewers: davidxl
> >
> > Reviewed By: davidxl
> >
> > Subscribers: xur, llvm-commits
> >
> > Differential Revision: https://reviews.llvm.org/D29954
> >
> > Added:
> > compiler-rt/trunk/test/profile/Linux/prctl.c
> > Modified:
> > compiler-rt/trunk/lib/profile/InstrProfilingFile.c
> > compiler-rt/trunk/lib/profile/InstrProfilingUtil.c
> > compiler-rt/trunk/lib/profile/InstrProfilingUtil.h
> >
> > Modified: compiler-rt/trunk/lib/profile/InstrProfilingFile.c
> > URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/
> profile/InstrProfilingFile.c?rev=295364&r1=295363&r2=295364&view=diff
> > ============================================================
> ==================
> > --- compiler-rt/trunk/lib/profile/InstrProfilingFile.c (original)
> > +++ compiler-rt/trunk/lib/profile/InstrProfilingFile.c Thu Feb 16
> 13:21:31 2017
> > @@ -530,6 +530,7 @@ int __llvm_profile_write_file(void) {
> > int rc, Length;
> > const char *Filename;
> > char *FilenameBuf;
> > + int PDeathSig = 0;
> >
> > if (lprofProfileDumped()) {
> > PROF_NOTE("Profile data not written to file: %s.\n",
> > @@ -556,10 +557,18 @@ int __llvm_profile_write_file(void) {
> > return -1;
> > }
> >
> > + // Temporarily suspend getting SIGKILL when the parent exits.
> > + PDeathSig = lprofSuspendSigKill();
> > +
> > /* Write profile data to the file. */
> > rc = writeFile(Filename);
> > if (rc)
> > PROF_ERR("Failed to write file \"%s\": %s\n", Filename,
> strerror(errno));
> > +
> > + // Restore SIGKILL.
> > + if (PDeathSig == 1)
> > + lprofRestoreSigKill();
> > +
> > return rc;
> > }
> >
> >
> > Modified: compiler-rt/trunk/lib/profile/InstrProfilingUtil.c
> > URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/
> profile/InstrProfilingUtil.c?rev=295364&r1=295363&r2=295364&view=diff
> > ============================================================
> ==================
> > --- compiler-rt/trunk/lib/profile/InstrProfilingUtil.c (original)
> > +++ compiler-rt/trunk/lib/profile/InstrProfilingUtil.c Thu Feb 16
> 13:21:31 2017
> > @@ -29,6 +29,11 @@
> > #include <stdlib.h>
> > #include <string.h>
> >
> > +#if defined(__linux__)
> > +#include <signal.h>
> > +#include <sys/prctl.h>
> > +#endif
> > +
> > COMPILER_RT_VISIBILITY
> > void __llvm_profile_recursive_mkdir(char *path) {
> > int i;
> > @@ -219,3 +224,24 @@ COMPILER_RT_VISIBILITY const char *lprof
> > #endif
> > return Sep;
> > }
> > +
> > +COMPILER_RT_VISIBILITY int lprofSuspendSigKill() {
> > +#if defined(__linux__)
> > + int PDeachSig = 0;
> > + /* Temporarily suspend getting SIGKILL upon exit of the parent
> process. */
> > + if (prctl(PR_GET_PDEATHSIG, &PDeachSig) == 0 && PDeachSig == SIGKILL)
> {
> > + fprintf(stderr, "set\n");
> > + prctl(PR_SET_PDEATHSIG, 0);
> > + }
> > + return (PDeachSig == SIGKILL);
> > +#else
> > + return 0;
> > +#endif
> > +}
> > +
> > +COMPILER_RT_VISIBILITY void lprofRestoreSigKill() {
> > +#if defined(__linux__)
> > + fprintf(stderr, "restore \n");
> > + prctl(PR_SET_PDEATHSIG, SIGKILL);
> > +#endif
> > +}
> >
> > Modified: compiler-rt/trunk/lib/profile/InstrProfilingUtil.h
> > URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/lib/
> profile/InstrProfilingUtil.h?rev=295364&r1=295363&r2=295364&view=diff
> > ============================================================
> ==================
> > --- compiler-rt/trunk/lib/profile/InstrProfilingUtil.h (original)
> > +++ compiler-rt/trunk/lib/profile/InstrProfilingUtil.h Thu Feb 16
> 13:21:31 2017
> > @@ -51,4 +51,12 @@ int lprofGetHostName(char *Name, int Len
> > unsigned lprofBoolCmpXchg(void **Ptr, void *OldV, void *NewV);
> > void *lprofPtrFetchAdd(void **Mem, long ByteIncr);
> >
> > +/* Temporarily suspend SIGKILL. Return value of 1 means a restore is
> needed.
> > + * Other return values mean no restore is needed.
> > + */
> > +int lprofSuspendSigKill();
> > +
> > +/* Restore previously suspended SIGKILL. */
> > +void lprofRestoreSigKill();
> > +
> > #endif /* PROFILE_INSTRPROFILINGUTIL_H */
> >
> > Added: compiler-rt/trunk/test/profile/Linux/prctl.c
> > URL: http://llvm.org/viewvc/llvm-project/compiler-rt/trunk/
> test/profile/Linux/prctl.c?rev=295364&view=auto
> > ============================================================
> ==================
> > --- compiler-rt/trunk/test/profile/Linux/prctl.c (added)
> > +++ compiler-rt/trunk/test/profile/Linux/prctl.c Thu Feb 16 13:21:31
> 2017
> > @@ -0,0 +1,36 @@
> > +// RUN: %clang_pgogen -O2 -o %t %s
> > +// RUN: rm -rf default_*.profraw
> > +// RUN: %run %t && sleep 1
> > +// RUN: llvm-profdata show default_*.profraw 2>&1 | FileCheck %s
> > +
> > +#include <signal.h>
> > +#include <stdio.h>
> > +#include <stdlib.h>
> > +#include <sys/prctl.h>
> > +#include <unistd.h>
> > +
> > +#define FAKE_COUNT_SZ 2000000
> > +/* fake counts to increse the profile size. */
> > +unsigned long long __attribute__((section("__llvm_prf_cnts")))
> > +counts[FAKE_COUNT_SZ];
> > +
> > +int main(int argc, char **argv) {
> > + pid_t pid = fork();
> > + if (pid == 0) {
> > + int i;
> > + int sum = 0;
> > + /* child process: sleep 500us and get to runtime before the
> > + * main process exits. */
> > + prctl(PR_SET_PDEATHSIG, SIGKILL);
> > + usleep(500);
> > + for (i = 0; i < 5000; ++i)
> > + sum += i * i * i;
> > + printf("child process (%d): sum=%d\n", getpid(), sum);
> > + } else if (pid > 0) {
> > + /* parent process: sleep 100us to get into profile runtime first. */
> > + usleep(100);
> > + }
> > + return 0;
> > +}
> > +
> > +// CHECK-NOT: Empty raw profile file
> >
> >
> > _______________________________________________
> > llvm-commits mailing list
> > llvm-commits at lists.llvm.org
> > http://lists.llvm.org/cgi-bin/mailman/listinfo/llvm-commits
>
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