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Re: [PATCH] Speedup various nptl/tst-cancel20 and nptl/tst-cancel21 tests.
On 9/12/19 4:07 PM, Carlos O'Donell wrote:
On 9/12/19 8:15 AM, Stefan Liebler wrote:
Hi,
each of thease tests - tst-cancel20, tst-cancelx20, tst-cancel21,
tst-cancelx21 and tst-cancel21-static - runs for 8s.
do_one_test is called 4 times. Either in do_one_test (tst-cancel20.c)
or in tf (tst-cancel21.c) "sleep (1)" is called 2 times.
This patch reduces the sleep time. Using usleep (5ms) leads to a
runtime of one tst-cancel... invocation of roughly 40ms instead of 8s.
As the nptl tests run in sequence, this patch saves roughly 39s of
runtime for "make check".
Bye,
Stefan
ChangeLog:
* nptl/tst-cancel20.c (do_one_test): Reduce sleep times.
* nptl/tst-cancel21.c (tf): Likewise.
I see two possible solutions:
(a) Explain in detail why the sleep is needed, and why reducing
the sleep is safe.
(b) Remove the sleep and use proper barriers to provide the
synchronization the test is using sleep to accomplish.
Your current patch does (a) without explaining why it is safe
to reduce the sleep period, and that the test continues to test
what it was written to test.
Is it safe to reduce the sleep timing?
Why is it there?
Hi,
tst-cancel20.c cancels a thread and checks if all cleanup-handlers were
called in the correct order:
if (cleanups != 0x1234L)
{
printf ("called cleanups %lx\n", cleanups);
return 1;
}
These numbers belong to the cleanup-handlers called in the following
functions:
1 => sh_body (sets in_sh_body=1 and blocks in read)
2 => sh (SIGHUP signal-handler; is received after pthread_barrier_wait)
3 => tf_body (waits with pthread_barrier_wait and then blocks in read)
4 => tf (started via pthread_create in do_one_test)
do_one_test starts tf, sends SIGHUP after waiting for the barrier and
cancels the thread as soon as in_sh_body has been set to 1.
tst-cancel21.c differs in the fact, that there a thread sends SIGHUP and
cancels the main thread.
I've tried to just remove the sleeps. This works fine with tst-cancel20.
But with tst-cancelx20 (same code as tst-cancel20.c but compiled with
-fexceptions -fasynchronous-unwind-tables) it sometimes fails with:
called cleanups 124 => cleanup-handler in tf_body was not called.
In the "good" case, SIGHUP is received while tf_body is blocking in read.
In the "error" case, SIGHUP is received while tf_body is waiting in
pthread_barrier_wait.
(This occures on s390x in the same way as on e.g. x86_64; I've used gcc
version 9.1.1)
I've compiled the test with gcc -S -fverbose-asm. Here is the shortened
output:
tf_body:
.LFB28:
...
# tst-cancel20.c:75: int r = pthread_barrier_wait (&b);
brasl %r14,pthread_barrier_wait #,
...
# tst-cancel20.c:82: if (read (fd[0], &c, 1) == 1)
.LEHB4:
brasl %r14,read #,
...
.LEHE4:
...
.L25:
# ../sysdeps/nptl/pthread.h:612: __frame->__cancel_routine
(__frame->__cancel_arg);
lghi %r2,3 #,
brasl %r14,cl #,
...
brasl %r14,_Unwind_Resume #,
.cfi_endproc
.section .gcc_except_table
.LLSDA28:
.byte 0xff
.byte 0xff
.byte 0x1
.uleb128 .LLSDACSE28-.LLSDACSB28
.LLSDACSB28:
.uleb128 .LEHB4-.LFB28
.uleb128 .LEHE4-.LEHB4
.uleb128 .L25-.LFB28
.uleb128 0
.uleb128 .LEHB5-.LFB28
.uleb128 .LEHE5-.LEHB5
.uleb128 0
.uleb128 0
.LLSDACSE28:
According to the .gcc_except_table, the region with our cleanup-handler
starts - after pthread_barrier_wait - directly before the read call,
even though pthread_barrier_wait is within pthread_cleanup_push / pop:
tf_body (void)
{ ...
pthread_cleanup_push (cl, (void *) 3L);
int r = pthread_barrier_wait (&b);
...
if (read (fd[0], &c, 1) == 1)
...
read (fd[0], &c, 1);
pthread_cleanup_pop (0);
}
Is this behaviour intended?
The difference between those calls is "nothrow":
extern ssize_t read (int __fd, void *__buf, size_t __nbytes) ;
vs
extern int pthread_barrier_wait (pthread_barrier_t *__barrier)
__attribute__ ((__nothrow__)) __attribute__ ((__nonnull__ (1)));
Placing a e.g. a printf or read call just before pthread_barrier_wait
will lead to the inclusion of pthread_barrier_wait and the
cleanup-handler is called!
Now, I've removed the sleeps and also removed the pthread_barrier_wait.
Instead write to and read from a pipe is used to synchronizse tf_body
and do_one_test.
Please have a look at the attached patch.
Bye.
Stefan
commit 47847907fd2dae3201bf87096886c44d7801768b
Author: Stefan Liebler <stli@linux.ibm.com>
Date: Wed Sep 11 09:43:08 2019 +0200
Speedup various nptl/tst-cancel20 and nptl/tst-cancel21 tests.
Each of thease tests - tst-cancel20, tst-cancelx20, tst-cancel21,
tst-cancelx21 and tst-cancel21-static - runs for 8s.
do_one_test is called 4 times. Either in do_one_test (tst-cancel20.c)
or in tf (tst-cancel21.c) "sleep (1)" is called 2 times.
This patch removes the sleep which leads to a short runtime of one
tst-cancel... invocation and as the nptl tests run in sequence,
this patch saves roughly 39s of runtime for "make check".
Just removing the sleeps leads to fails in tst-cancelx20 / x21
as one cleanup-handler won't be called as pthread_barrier_wait is
marked with attribute ((__nothrow__)). Therefore the pthread_barrier_wait
calls are replaced by writing to and reading from a pipe in order
to synchronize the threads.
ChangeLog:
* nptl/tst-cancel20.c (b): Remove.
(fd): Enhance to 6 elements.
(tf_body): Use xwrite instead of pthread_barrier_wait.
(do_one_test): Remove sleep and use read instead of
pthread_barrier_wait.
* nptl/tst-cancel21.c (b): Remove.
(fd): Enhance to 6 elements.
(tf_body): Use xwrite instead of pthread_barrier_wait.
(tf): Remove sleep and use read instead of
pthread_barrier_wait.
diff --git a/nptl/tst-cancel20.c b/nptl/tst-cancel20.c
index 96dfb71fa9..f82f899a83 100644
--- a/nptl/tst-cancel20.c
+++ b/nptl/tst-cancel20.c
@@ -21,11 +21,10 @@
#include <signal.h>
#include <stdio.h>
#include <stdlib.h>
-#include <unistd.h>
+#include <support/xunistd.h>
-static int fd[4];
-static pthread_barrier_t b;
+static int fd[6];
volatile int in_sh_body;
unsigned long cleanups;
@@ -68,17 +67,21 @@ sh (int sig)
static void __attribute__((noinline))
tf_body (void)
{
- char c;
+ char c = 0;
pthread_cleanup_push (cl, (void *) 3L);
- int r = pthread_barrier_wait (&b);
- if (r != 0 && r != PTHREAD_BARRIER_SERIAL_THREAD)
- {
- puts ("child thread: barrier_wait failed");
- exit (1);
- }
-
+ /* Write to the pipe in order to inform do_one_test that we are now within
+ pthread_cleanup_push / pop and do_one_test can send us SIGHUP and cancel
+ this thread.
+ We do not use pthread_barrier_wait here as it is marked with
+ attribute ((__nothrow__)) and the region in .gcc_except_table section
+ which is responsible for calling the cleanup-handler would start just
+ before the next call to read in case of nptl/tst-cancelx20.c where we
+ build with "gcc -fexceptions -fasynchronous-unwind-tables". */
+ xwrite (fd[5], &c, 1);
+
+ /* Blocks until either SIGHUP is received or the thread is canceled. */
if (read (fd[0], &c, 1) == 1)
{
puts ("read succeeded");
@@ -106,7 +109,7 @@ do_one_test (void)
{
in_sh_body = 0;
cleanups = 0;
- if (pipe (fd) != 0 || pipe (fd + 2) != 0)
+ if (pipe (fd) != 0 || pipe (fd + 2) != 0 || pipe (fd + 4) != 0)
{
puts ("pipe failed");
return 1;
@@ -119,16 +122,17 @@ do_one_test (void)
return 1;
}
- int r = pthread_barrier_wait (&b);
- if (r != 0 && r != PTHREAD_BARRIER_SERIAL_THREAD)
+ /* Block until the thread is within pthread_cleanup_push / pop
+ in tf_body which is called by tf. */
+ char c;
+ if (read (fd[4], &c, 1) != 1)
{
- puts ("parent thread: barrier_wait failed");
+ printf ("parent thread: Reading from pipe failed %m\n");
return 1;
}
- sleep (1);
-
- r = pthread_kill (th, SIGHUP);
+ /* Send signal SIGHUP where in_sh_body will be set to 1 in sh_body. */
+ int r = pthread_kill (th, SIGHUP);
if (r)
{
errno = r;
@@ -137,8 +141,9 @@ do_one_test (void)
}
while (in_sh_body == 0)
- sleep (1);
+ ;
+ /* Cancel the thread while the signal handler blocks in read in sh_body. */
if (pthread_cancel (th) != 0)
{
puts ("cancel failed");
@@ -172,6 +177,8 @@ do_one_test (void)
close (fd[1]);
close (fd[2]);
close (fd[3]);
+ close (fd[4]);
+ close (fd[5]);
return 0;
}
@@ -195,12 +202,6 @@ do_test (void)
return 1;
}
- if (pthread_barrier_init (&b, NULL, 2) != 0)
- {
- puts ("barrier_init failed");
- return 1;
- }
-
struct sigaction sa;
sa.sa_handler = sh;
sigemptyset (&sa.sa_mask);
diff --git a/nptl/tst-cancel21.c b/nptl/tst-cancel21.c
index 361510b027..30e396dee2 100644
--- a/nptl/tst-cancel21.c
+++ b/nptl/tst-cancel21.c
@@ -22,11 +22,10 @@
#include <stdio.h>
#include <stdlib.h>
#include <sys/wait.h>
-#include <unistd.h>
+#include <support/xunistd.h>
-static int fd[4];
-static pthread_barrier_t b;
+static int fd[6];
volatile int in_sh_body;
unsigned long cleanups;
@@ -69,17 +68,21 @@ sh (int sig)
static void __attribute__((noinline))
tf_body (void)
{
- char c;
+ char c = 0;
pthread_cleanup_push (cl, (void *) 3L);
- int r = pthread_barrier_wait (&b);
- if (r != 0 && r != PTHREAD_BARRIER_SERIAL_THREAD)
- {
- puts ("child thread: barrier_wait failed");
- exit (1);
- }
-
+ /* Write to the pipe in order to inform tf that we are now within
+ pthread_cleanup_push / pop and tf can send us SIGHUP and cancel
+ this thread.
+ We do not use pthread_barrier_wait here as it is marked with
+ attribute ((__nothrow__)) and the region in .gcc_except_table section
+ which is responsible for calling the cleanup-handler would start just
+ before the next call to read in case of nptl/tst-cancelx21.c where we
+ build with "gcc -fexceptions -fasynchronous-unwind-tables". */
+ xwrite (fd[5], &c, 1);
+
+ /* Blocks until either SIGHUP is received or the thread is canceled. */
if (read (fd[0], &c, 1) == 1)
{
puts ("read succeeded");
@@ -97,16 +100,17 @@ tf (void *arg)
{
pthread_t th = (pthread_t) arg;
- int r = pthread_barrier_wait (&b);
- if (r != 0 && r != PTHREAD_BARRIER_SERIAL_THREAD)
+ /* Block until the main thread is within pthread_cleanup_push / pop
+ in tf_body which is called by do_one_test. */
+ char c;
+ if (read (fd[4], &c, 1) != 1)
{
- puts ("parent thread: barrier_wait failed");
+ printf ("Reading from pipe failed %m\n");
exit (1);
}
- sleep (1);
-
- r = pthread_kill (th, SIGHUP);
+ /* Send signal SIGHUP where in_sh_body will be set to 1 in sh_body. */
+ int r = pthread_kill (th, SIGHUP);
if (r)
{
errno = r;
@@ -115,8 +119,10 @@ tf (void *arg)
}
while (in_sh_body == 0)
- sleep (1);
+ ;
+ /* Cancel the parent thread while the signal handler blocks in read
+ in sh_body. */
if (pthread_cancel (th) != 0)
{
puts ("cancel failed");
@@ -142,11 +148,6 @@ tf (void *arg)
exit (1);
}
- if (pthread_barrier_destroy (&b))
- {
- puts ("barrier destroy failed");
- exit (1);
- }
/* The pipe closing must be issued after the cancellation handling to avoid
a race condition where the cancellation runs after both pipe ends are
@@ -156,6 +157,8 @@ tf (void *arg)
close (fd[1]);
close (fd[2]);
close (fd[3]);
+ close (fd[4]);
+ close (fd[5]);
exit (0);
}
@@ -186,14 +189,8 @@ do_one_test (void)
return !WIFEXITED (status) || WEXITSTATUS (status);
}
- if (pthread_barrier_init (&b, NULL, 2) != 0)
- {
- puts ("barrier_init failed");
- exit (1);
- }
-
cleanups = 0;
- if (pipe (fd) != 0 || pipe (fd + 2) != 0)
+ if (pipe (fd) != 0 || pipe (fd + 2) != 0 || pipe (fd + 4) != 0)
{
puts ("pipe failed");
exit (1);