On Wed, 10 Aug 2022 17:30:41 -0300 Murilo Opsfelder Araújo <muri...@linux.ibm.com> wrote:
> Hi, Claudio. Hi Murilo, [...] > I've smoke-tested this on ppc and everything looks fine. > For what's worth: > > Reviewed-by: Murilo Opsfelder Araujo <muri...@linux.ibm.com> > Tested-by: Murilo Opsfelder Araujo <muri...@linux.ibm.com> thanks a lot for testing this! > > > Have you measured the benefits of using -async-teardown vs. not using it? > If so, can you please share the details so I can give it a try on ppc, too? > > The wall-clock perception is that nothing has changed, for better or worse. > My tests used mid-sized VMs, like 128 vCPUs, 64GB RAM. The number of CPUs doesn't really have any impact. 64G of RAM is quite small to notice a sizeable difference, although you should be able to see a few seconds of speedup in the shutdown. Also, starting a guest with a lot of RAM is not enough, you have to make sure that the guest ram is actually allocated (completely fill the ram in the guest before shutting it down) I just tested a 64G and a 256G guest on s390x. I measured the time between the last line in the console ("Reached target Power-Off.") and the moment when control comes back to the shell. The measurement was not exactly super accurate (I manually ran "date +%s" in another shell when I saw the last line in the console, and then again when I got the shell back from qemu). The 64G guest needs a few seconds, the 256G needs almost exactly 4 times as much. With the asynchronous teardown it's almost instant in both cases (less than 1s, too fast to measure manually). Try a multi-TB guest if you can (at the moment I can't) to see a more marked effect. Also consider that this is for _normal_ guests. Protected guests on s390x have an even slower teardown due to the way protected virtualization is implemented in the hardware. I hope this was helpful > > Cheers! > > > --- > > include/qemu/async-teardown.h | 22 ++++++ > > os-posix.c | 6 ++ > > qemu-options.hx | 17 +++++ > > util/async-teardown.c | 123 ++++++++++++++++++++++++++++++++++ > > util/meson.build | 1 + > > 5 files changed, 169 insertions(+) > > create mode 100644 include/qemu/async-teardown.h > > create mode 100644 util/async-teardown.c > > > > diff --git a/include/qemu/async-teardown.h b/include/qemu/async-teardown.h > > new file mode 100644 > > index 0000000000..092e7a37e7 > > --- /dev/null > > +++ b/include/qemu/async-teardown.h > > @@ -0,0 +1,22 @@ > > +/* > > + * Asynchronous teardown > > + * > > + * Copyright IBM, Corp. 2022 > > + * > > + * Authors: > > + * Claudio Imbrenda <imbre...@linux.ibm.com> > > + * > > + * This work is licensed under the terms of the GNU GPL, version 2 or (at > > your > > + * option) any later version. See the COPYING file in the top-level > > directory. > > + * > > + */ > > +#ifndef QEMU_ASYNC_TEARDOWN_H > > +#define QEMU_ASYNC_TEARDOWN_H > > + > > +#include "config-host.h" > > + > > +#ifdef CONFIG_LINUX > > +void init_async_teardown(void); > > +#endif > > + > > +#endif > > diff --git a/os-posix.c b/os-posix.c > > index 321fc4bd13..4858650c3e 100644 > > --- a/os-posix.c > > +++ b/os-posix.c > > @@ -39,6 +39,7 @@ > > > > #ifdef CONFIG_LINUX > > #include <sys/prctl.h> > > +#include "qemu/async-teardown.h" > > #endif > > > > /* > > @@ -150,6 +151,11 @@ int os_parse_cmd_args(int index, const char *optarg) > > case QEMU_OPTION_daemonize: > > daemonize = 1; > > break; > > +#if defined(CONFIG_LINUX) > > + case QEMU_OPTION_asyncteardown: > > + init_async_teardown(); > > + break; > > +#endif > > default: > > return -1; > > } > > diff --git a/qemu-options.hx b/qemu-options.hx > > index 3f23a42fa8..d434353159 100644 > > --- a/qemu-options.hx > > +++ b/qemu-options.hx > > @@ -4743,6 +4743,23 @@ HXCOMM Internal use > > DEF("qtest", HAS_ARG, QEMU_OPTION_qtest, "", QEMU_ARCH_ALL) > > DEF("qtest-log", HAS_ARG, QEMU_OPTION_qtest_log, "", QEMU_ARCH_ALL) > > > > +#ifdef __linux__ > > +DEF("async-teardown", 0, QEMU_OPTION_asyncteardown, > > + "-async-teardown enable asynchronous teardown\n", > > + QEMU_ARCH_ALL) > > +#endif > > +SRST > > +``-async-teardown`` > > + Enable asynchronous teardown. A new teardown process will be > > + created at startup, using clone. The teardown process will share > > + the address space of the main qemu process, and wait for the main > > + process to terminate. At that point, the teardown process will > > + also exit. This allows qemu to terminate quickly if the guest was > > + huge, leaving the teardown of the address space to the teardown > > + process. Since the teardown process shares the same cgroups as the > > + main qemu process, accounting is performed correctly. > > +ERST > > + > > DEF("msg", HAS_ARG, QEMU_OPTION_msg, > > "-msg [timestamp[=on|off]][,guest-name=[on|off]]\n" > > " control error message format\n" > > diff --git a/util/async-teardown.c b/util/async-teardown.c > > new file mode 100644 > > index 0000000000..07fe549891 > > --- /dev/null > > +++ b/util/async-teardown.c > > @@ -0,0 +1,123 @@ > > +/* > > + * Asynchronous teardown > > + * > > + * Copyright IBM, Corp. 2022 > > + * > > + * Authors: > > + * Claudio Imbrenda <imbre...@linux.ibm.com> > > + * > > + * This work is licensed under the terms of the GNU GPL, version 2 or (at > > your > > + * option) any later version. See the COPYING file in the top-level > > directory. > > + * > > + */ > > +#include <stdlib.h> > > +#include <stdio.h> > > +#include <sys/types.h> > > +#include <sys/unistd.h> > > +#include <dirent.h> > > +#include <sys/prctl.h> > > +#include <signal.h> > > +#include <sched.h> > > + > > +#include "qemu/async-teardown.h" > > + > > +static pid_t the_ppid; > > + > > +/* > > + * Close all open file descriptors. > > + */ > > +static void close_all_open_fd(void) > > +{ > > + struct dirent *de; > > + int fd, dfd; > > + DIR *dir; > > + > > + dir = opendir("/proc/self/fd"); > > + if (!dir) { > > + return; > > + } > > + /* Avoid closing the directory. */ > > + dfd = dirfd(dir); > > + > > + for (de = readdir(dir); de; de = readdir(dir)) { > > + fd = atoi(de->d_name); > > + if (fd != dfd) { > > + close(fd); > > + } > > + } > > + closedir(dir); > > +} > > + > > +static void hup_handler(int signal) > > +{ > > + /* Check every second if this process has been reparented. */ > > + while (the_ppid == getppid()) { > > + /* sleep() is safe to use in a signal handler. */ > > + sleep(1); > > + } > > + > > + /* At this point the parent process has terminated completely. */ > > + _exit(0); > > +} > > + > > +static int async_teardown_fn(void *arg) > > +{ > > + struct sigaction sa = { .sa_handler = hup_handler }; > > + sigset_t hup_signal; > > + char name[16]; > > + > > + /* Set a meaningful name for this process. */ > > + snprintf(name, 16, "cleanup/%d", the_ppid); > > + prctl(PR_SET_NAME, (unsigned long)name); > > + > > + /* > > + * Close all file descriptors that might have been inherited from the > > + * main qemu process when doing clone, needed to make libvirt happy. > > + * Not using close_range for increased compatibility with older > > kernels. > > + */ > > + close_all_open_fd(); > > + > > + /* Set up a handler for SIGHUP and unblock SIGHUP. */ > > + sigaction(SIGHUP, &sa, NULL); > > + sigemptyset(&hup_signal); > > + sigaddset(&hup_signal, SIGHUP); > > + sigprocmask(SIG_UNBLOCK, &hup_signal, NULL); > > + > > + /* Ask to receive SIGHUP when the parent dies. */ > > + prctl(PR_SET_PDEATHSIG, SIGHUP); > > + > > + /* > > + * Sleep forever, unless the parent process has already terminated. The > > + * only interruption can come from the SIGHUP signal, which in normal > > + * operation is received when the parent process dies. > > + */ > > + if (the_ppid == getppid()) { > > + pause(); > > + } > > + > > + /* At this point the parent process has terminated completely. */ > > + _exit(0); > > +} > > + > > +/* > > + * Block all signals, start (clone) a new process sharing the address space > > + * with qemu (CLONE_VM), then restore signals. > > + */ > > +void init_async_teardown(void) > > +{ > > + sigset_t all_signals, old_signals; > > + const int stack_size = 8192; /* Should be more than enough */ > > + char *stack, *stack_ptr; > > + > > + the_ppid = getpid(); > > + stack = malloc(stack_size); > > + if (!stack) { > > + return; > > + } > > + stack_ptr = stack + stack_size; > > + > > + sigfillset(&all_signals); > > + sigprocmask(SIG_BLOCK, &all_signals, &old_signals); > > + clone(async_teardown_fn, stack_ptr, CLONE_VM, NULL, NULL, NULL, NULL); > > + sigprocmask(SIG_SETMASK, &old_signals, NULL); > > +} > > diff --git a/util/meson.build b/util/meson.build > > index 5e282130df..63acd59bb0 100644 > > --- a/util/meson.build > > +++ b/util/meson.build > > @@ -2,6 +2,7 @@ util_ss.add(files('osdep.c', 'cutils.c', 'unicode.c', > > 'qemu-timer-common.c')) > > if not config_host_data.get('CONFIG_ATOMIC64') > > util_ss.add(files('atomic64.c')) > > endif > > +util_ss.add(when: 'CONFIG_LINUX', if_true: files('async-teardown.c')) > > util_ss.add(when: 'CONFIG_POSIX', if_true: files('aio-posix.c')) > > util_ss.add(when: 'CONFIG_POSIX', if_true: files('fdmon-poll.c')) > > if config_host_data.get('CONFIG_EPOLL_CREATE1') > >