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From: "mjbaars1977 at gmail dot com" <sourceware-bugzilla@sourceware.org> To: glibc-bugs@sourceware.org Subject: [Bug libc/29585] New: sched_getcpu returns invalid results Date: Mon, 19 Sep 2022 08:22:30 +0000 [thread overview] Message-ID: <bug-29585-131@http.sourceware.org/bugzilla/> (raw) https://sourceware.org/bugzilla/show_bug.cgi?id=29585 Bug ID: 29585 Summary: sched_getcpu returns invalid results Product: glibc Version: 2.35 Status: UNCONFIRMED Severity: normal Priority: P2 Component: libc Assignee: unassigned at sourceware dot org Reporter: mjbaars1977 at gmail dot com CC: drepper.fsp at gmail dot com Target Milestone: --- Hello, I noticed the following while I was trying SCHED_FIFO, because FIFO processes are not supposed to migrate from processor to processor. When looking at the manual page of sched_getcpu(), it states that: The call cpu = sched_getcpu(); is equivalent to the following getcpu(2) call: int c, s; s = getcpu(&c, NULL, NULL); cpu = (s == -1) ? s : c; But when you compare the output of these two in a multi-threaded program (using clone()), the two produce very different outcomes. Only the second one will give you the right answer. The results can be reproduced with sched_setaffinity() before calling clone() and a call to both methods above from within the child process. My version uses a timer_create() to make this call periodically. sched_get_cpu_timer_init(0); // core_from = sched_get_cpu() + 1; double x = 1.0; double y = (double) (random() + 1) * 1.00E-19f; for (long i = 0; i < ((long) 1 << 32); i++) x *= 1.00f + y; // sleep (1); // usleep (random() % 1000000L); // core_upto = sched_get_cpu() + 1; sched_get_cpu_timer_free(); Compilation is done with -Ofast -mfpmath=387 -fno-toplevel-reorder, for sake of completeness. Best regards, Mischa Baars. -- You are receiving this mail because: You are on the CC list for the bug.
next reply other threads:[~2022-09-19 8:22 UTC|newest] Thread overview: 26+ messages / expand[flat|nested] mbox.gz Atom feed top 2022-09-19 8:22 mjbaars1977 at gmail dot com [this message] 2022-09-19 14:21 ` [Bug libc/29585] " fweimer at redhat dot com 2022-09-21 8:00 ` mjbaars1977 at gmail dot com 2022-09-22 8:30 ` mjbaars1977 at gmail dot com 2022-09-22 12:59 ` mjbaars1977 at gmail dot com 2022-09-22 13:00 ` mjbaars1977 at gmail dot com 2022-09-26 8:04 ` mjbaars1977 at gmail dot com 2022-09-26 9:18 ` fweimer at redhat dot com 2022-09-26 11:14 ` mjbaars1977 at gmail dot com 2022-09-26 11:21 ` fweimer at redhat dot com 2022-09-26 12:15 ` mjbaars1977 at gmail dot com 2022-09-28 9:59 ` mjbaars1977 at gmail dot com 2022-09-28 10:09 ` schwab@linux-m68k.org 2022-09-28 14:03 ` mjbaars1977 at gmail dot com 2022-10-10 9:18 ` fweimer at redhat dot com 2022-10-10 15:14 ` mjbaars1977 at gmail dot com 2022-10-10 16:20 ` mjbaars1977 at gmail dot com 2022-10-10 16:31 ` fweimer at redhat dot com 2022-10-10 16:41 ` mjbaars1977 at gmail dot com 2022-10-10 17:05 ` mjbaars1977 at gmail dot com 2022-10-10 17:09 ` schwab@linux-m68k.org 2022-10-10 17:10 ` mjbaars1977 at gmail dot com 2022-11-14 9:58 ` mjbaars1977 at gmail dot com 2022-11-14 12:55 ` fweimer at redhat dot com 2022-11-14 16:15 ` mjbaars1977 at gmail dot com 2022-11-14 16:40 ` mjbaars1977 at gmail dot com
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