marcandre.lur...@redhat.com writes: > From: Marc-André Lureau <marcandre.lur...@redhat.com> > > Thanks to the monitors coroutine support, the screendump handler can
monitors' Suggest to add (merge commit b7092cda1b3) right before the comma. > trigger a graphic_hw_update(), yield and let the main loop run until > update is done. Then the handler is resumed, and ppm_save() will write > the screen image to disk in the coroutine context (thus non-blocking). > > Potentially, during non-blocking write, some new graphic update could > happen, and thus the image may have some glitches. Whether that > behaviour is acceptable is discutable. Allocating new memory may not be s/discutable/debatable/ > a good idea, as framebuffers can be quite large. Even then, QEMU may > become less responsive as it requires paging in etc. Tradeoff. I'm okay with "simple & efficient, but might glitch". It should be documented, though. Followup patch is fine. > Related to: > https://bugzilla.redhat.com/show_bug.cgi?id=1230527 > > Signed-off-by: Marc-André Lureau <marcandre.lur...@redhat.com> > --- > hmp-commands.hx | 1 + > monitor/hmp-cmds.c | 3 ++- > qapi/ui.json | 3 ++- > ui/console.c | 27 ++++++++++++++++++++++++--- > 4 files changed, 29 insertions(+), 5 deletions(-) > > diff --git a/hmp-commands.hx b/hmp-commands.hx > index cd068389de..ff2d7aa8f3 100644 > --- a/hmp-commands.hx > +++ b/hmp-commands.hx > @@ -254,6 +254,7 @@ ERST > .help = "save screen from head 'head' of display device > 'device' " > "into PPM image 'filename'", > .cmd = hmp_screendump, > + .coroutine = true, > }, > > SRST > diff --git a/monitor/hmp-cmds.c b/monitor/hmp-cmds.c > index 9789f4277f..91608bac6d 100644 > --- a/monitor/hmp-cmds.c > +++ b/monitor/hmp-cmds.c > @@ -1756,7 +1756,8 @@ err_out: > goto out; > } > > -void hmp_screendump(Monitor *mon, const QDict *qdict) > +void coroutine_fn > +hmp_screendump(Monitor *mon, const QDict *qdict) > { > const char *filename = qdict_get_str(qdict, "filename"); > const char *id = qdict_get_try_str(qdict, "device"); > diff --git a/qapi/ui.json b/qapi/ui.json > index 9d6721037f..6c7b33cb72 100644 > --- a/qapi/ui.json > +++ b/qapi/ui.json > @@ -98,7 +98,8 @@ > # > ## > { 'command': 'screendump', > - 'data': {'filename': 'str', '*device': 'str', '*head': 'int'} } > + 'data': {'filename': 'str', '*device': 'str', '*head': 'int'}, > + 'coroutine': true } > > ## > # == Spice > diff --git a/ui/console.c b/ui/console.c > index a56fe0dd26..0118f70d9a 100644 > --- a/ui/console.c > +++ b/ui/console.c > @@ -168,6 +168,7 @@ struct QemuConsole { > QEMUFIFO out_fifo; > uint8_t out_fifo_buf[16]; > QEMUTimer *kbd_timer; > + CoQueue dump_queue; > > QTAILQ_ENTRY(QemuConsole) next; > }; > @@ -263,6 +264,7 @@ static void gui_setup_refresh(DisplayState *ds) > > void graphic_hw_update_done(QemuConsole *con) > { > + qemu_co_queue_restart_all(&con->dump_queue); > } > > void graphic_hw_update(QemuConsole *con) > @@ -340,8 +342,15 @@ static bool ppm_save(int fd, pixman_image_t *image, > Error **errp) > return true; > } > > -void qmp_screendump(const char *filename, bool has_device, const char > *device, > - bool has_head, int64_t head, Error **errp) > +static void graphic_hw_update_bh(void *con) > +{ > + graphic_hw_update(con); > +} > + > +/* Safety: coroutine-only, concurrent-coroutine safe, main thread only */ > +void coroutine_fn > +qmp_screendump(const char *filename, bool has_device, const char *device, > + bool has_head, int64_t head, Error **errp) > { > g_autoptr(pixman_image_t) image = NULL; > QemuConsole *con; > @@ -366,7 +375,15 @@ void qmp_screendump(const char *filename, bool > has_device, const char *device, > } > } > > - graphic_hw_update(con); > + if (qemu_co_queue_empty(&con->dump_queue)) { > + /* Defer the update, it will restart the pending coroutines */ > + aio_bh_schedule_oneshot(qemu_get_aio_context(), > + graphic_hw_update_bh, con); > + } > + qemu_co_queue_wait(&con->dump_queue, NULL); > + > + /* All pending coroutines are woken up, while BQL taken, no further > graphic > + * update are possible until it is released, take an image ref before > that. */ "while BQL taken": I guess you mean "while the BQL is held". Style nit: CODING_STYLE.rst asks for wings. Recommend to limit comment line length for readability. Recommend to turn a few commas into periods. Together: /* * All pending coroutines are woken up, while the BQL is held. No * further graphic update are possible until it is released. Take * an image ref before that. */ > surface = qemu_console_surface(con); > if (!surface) { > error_setg(errp, "no surface"); > @@ -381,6 +398,9 @@ void qmp_screendump(const char *filename, bool > has_device, const char *device, > return; > } > > + /* The image content could potentially be updated as the coroutine yields > + * and releases the BQL. It could produce corrupted dump, but it should > be > + * otherwise safe. */ Similar nit. /* * The image content could potentially be updated as the coroutine * yields and releases the BQL. It could produce corrupted dump, but * it should be otherwise safe. */ > if (!ppm_save(fd, image, errp)) { > qemu_unlink(filename); > } > @@ -1297,6 +1317,7 @@ static QemuConsole *new_console(DisplayState *ds, > console_type_t console_type, > > obj = object_new(TYPE_QEMU_CONSOLE); > s = QEMU_CONSOLE(obj); > + qemu_co_queue_init(&s->dump_queue); > s->head = head; > object_property_add_link(obj, "device", TYPE_DEVICE, > (Object **)&s->device, Simpler than v1 thanks to coroutine support for HMP, and the use of CoQueue. Let's revisit the experiment I did for v1: "observe the main loop keeps running while the screendump does its work". Message-ID: <87a74ueudt....@dusky.pond.sub.org> https://lists.nongnu.org/archive/html/qemu-devel/2020-03/msg01235.html I repeated the first experiment "does the main loop continue to run when writing out the screendump blocks / would block?" Same result: main loop remains blocked. Back then, you replied Right, the goal was rather originally to fix rhbz#1230527. We got coroutine IO by accident, and I was too optimistic about default behaviour change ;) I will update the patch. I'm unsure what exactly the update is. Is it the change from Fixes: https://bugzilla.redhat.com/show_bug.cgi?id=1230527 to Related to: https://bugzilla.redhat.com/show_bug.cgi?id=1230527 ? The commit message says "ppm_save() will write the screen image to disk in the coroutine context (thus non-blocking)." Sure reads like a claim the main loop is no longer blocked. It is blocked, at least for me. Please clarify. Back then, I proposed a second experiment: "does the main loop continue to run while we wait for graphic_hw_update_done()?" I don't know the result. Do you? The commit message claims "the screendump handler can trigger a graphic_hw_update(), yield and let the main loop run until update is done."
