* Alexey (a.pereva...@samsung.com) wrote:
> On Tue, May 09, 2017 at 08:01:01PM +0100, Dr. David Alan Gilbert wrote:
> > * Alexey (a.pereva...@samsung.com) wrote:
> > > On Tue, May 09, 2017 at 10:40:34AM +0100, Dr. David Alan Gilbert wrote:
> > > > * Peter Xu (pet...@redhat.com) wrote:
> > > > > On Mon, May 08, 2017 at 12:08:07PM +0300, Alexey wrote:
> > > > > > On Mon, May 08, 2017 at 02:29:06PM +0800, Peter Xu wrote:
> > > > > > > On Fri, Apr 28, 2017 at 02:11:19PM +0300, Alexey Perevalov wrote:
> > > > > > > > On 04/28/2017 01:00 PM, Peter Xu wrote:
> > > > > > > > >On Fri, Apr 28, 2017 at 09:57:37AM +0300, Alexey Perevalov
> > > > > > > > >wrote:
> > > > > > > > >>This patch provides downtime calculation per vCPU,
> > > > > > > > >>as a summary and as a overlapped value for all vCPUs.
> > > > > > > > >>
> > > > > > > > >>This approach was suggested by Peter Xu, as an improvements of
> > > > > > > > >>previous approch where QEMU kept tree with faulted page
> > > > > > > > >>address and cpus bitmask
> > > > > > > > >>in it. Now QEMU is keeping array with faulted page address as
> > > > > > > > >>value and vCPU
> > > > > > > > >>as index. It helps to find proper vCPU at UFFD_COPY time.
> > > > > > > > >>Also it keeps
> > > > > > > > >>list for downtime per vCPU (could be traced with
> > > > > > > > >>page_fault_addr)
> > > > > > > > >>
> > > > > > > > >>For more details see comments for get_postcopy_total_downtime
> > > > > > > > >>implementation.
> > > > > > > > >>
> > > > > > > > >>Downtime will not calculated if postcopy_downtime field of
> > > > > > > > >>MigrationIncomingState wasn't initialized.
> > > > > > > > >>
> > > > > > > > >>Signed-off-by: Alexey Perevalov <a.pereva...@samsung.com>
> > > > > > > > >>---
> > > > > > > > >> include/migration/migration.h | 3 ++
> > > > > > > > >> migration/migration.c | 103
> > > > > > > > >> ++++++++++++++++++++++++++++++++++++++++++
> > > > > > > > >> migration/postcopy-ram.c | 20 +++++++-
> > > > > > > > >> migration/trace-events | 6 ++-
> > > > > > > > >> 4 files changed, 130 insertions(+), 2 deletions(-)
> > > > > > > > >>
> > > > > > > > >>diff --git a/include/migration/migration.h
> > > > > > > > >>b/include/migration/migration.h
> > > > > > > > >>index e8fb68f..a22f9ce 100644
> > > > > > > > >>--- a/include/migration/migration.h
> > > > > > > > >>+++ b/include/migration/migration.h
> > > > > > > > >>@@ -139,6 +139,9 @@ void
> > > > > > > > >>migration_incoming_state_destroy(void);
> > > > > > > > >> * Functions to work with downtime context
> > > > > > > > >> */
> > > > > > > > >> struct DowntimeContext *downtime_context_new(void);
> > > > > > > > >>+void mark_postcopy_downtime_begin(uint64_t addr, int cpu);
> > > > > > > > >>+void mark_postcopy_downtime_end(uint64_t addr);
> > > > > > > > >>+uint64_t get_postcopy_total_downtime(void);
> > > > > > > > >> struct MigrationState
> > > > > > > > >> {
> > > > > > > > >>diff --git a/migration/migration.c b/migration/migration.c
> > > > > > > > >>index ec76e5c..2c6f150 100644
> > > > > > > > >>--- a/migration/migration.c
> > > > > > > > >>+++ b/migration/migration.c
> > > > > > > > >>@@ -2150,3 +2150,106 @@ PostcopyState
> > > > > > > > >>postcopy_state_set(PostcopyState new_state)
> > > > > > > > >> return atomic_xchg(&incoming_postcopy_state, new_state);
> > > > > > > > >> }
> > > > > > > > >>+void mark_postcopy_downtime_begin(uint64_t addr, int cpu)
> > > > > > > > >>+{
> > > > > > > > >>+ MigrationIncomingState *mis =
> > > > > > > > >>migration_incoming_get_current();
> > > > > > > > >>+ DowntimeContext *dc;
> > > > > > > > >>+ if (!mis->downtime_ctx || cpu < 0) {
> > > > > > > > >>+ return;
> > > > > > > > >>+ }
> > > > > > > > >>+ dc = mis->downtime_ctx;
> > > > > > > > >>+ dc->vcpu_addr[cpu] = addr;
> > > > > > > > >>+ dc->last_begin = dc->page_fault_vcpu_time[cpu] =
> > > > > > > > >>+ qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> > > > > > > > >>+
> > > > > > > > >>+ trace_mark_postcopy_downtime_begin(addr, dc,
> > > > > > > > >>dc->page_fault_vcpu_time[cpu],
> > > > > > > > >>+ cpu);
> > > > > > > > >>+}
> > > > > > > > >>+
> > > > > > > > >>+void mark_postcopy_downtime_end(uint64_t addr)
> > > > > > > > >>+{
> > > > > > > > >>+ MigrationIncomingState *mis =
> > > > > > > > >>migration_incoming_get_current();
> > > > > > > > >>+ DowntimeContext *dc;
> > > > > > > > >>+ int i;
> > > > > > > > >>+ bool all_vcpu_down = true;
> > > > > > > > >>+ int64_t now;
> > > > > > > > >>+
> > > > > > > > >>+ if (!mis->downtime_ctx) {
> > > > > > > > >>+ return;
> > > > > > > > >>+ }
> > > > > > > > >>+ dc = mis->downtime_ctx;
> > > > > > > > >>+ now = qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
> > > > > > > > >>+
> > > > > > > > >>+ /* check all vCPU down,
> > > > > > > > >>+ * QEMU has bitmap.h, but even with bitmap_and
> > > > > > > > >>+ * will be a cycle */
> > > > > > > > >>+ for (i = 0; i < smp_cpus; i++) {
> > > > > > > > >>+ if (dc->vcpu_addr[i]) {
> > > > > > > > >>+ continue;
> > > > > > > > >>+ }
> > > > > > > > >>+ all_vcpu_down = false;
> > > > > > > > >>+ break;
> > > > > > > > >>+ }
> > > > > > > > >>+
> > > > > > > > >>+ if (all_vcpu_down) {
> > > > > > > > >>+ dc->total_downtime += now - dc->last_begin;
> > > > > > > > >Shall we do this accouting only if we are sure the copied page
> > > > > > > > >address
> > > > > > > > >is one of the page faulted addresses? Can it be some other
> > > > > > > > >page? I
> > > > > > > > >don't know. But since we have the loop below to make sure of
> > > > > > > > >it, why
> > > > > > > > >not?
> > > > > > > > no, the downtime implies since page fault till the
> > > > > > > > page will be copied.
> > > > > > > > Yes another pages could be copied as well as pagefaulted,
> > > > > > > > and they are copied due to prefetching, but it's not a downtime.
> > > > > > >
> > > > > > > Not sure I got the point... Do you mean that when reach here, then
> > > > > > > this page address is definitely one of the faulted addresses? I
> > > > > > > am not
> > > > > > > 100% sure of this, but if you are sure, I am okay with it.
> > > > > > Let me clarify.
> > > > > >
> > > > > > > > >Shall we do this accouting only if we are sure the copied page
> > > > > > > > >address
> > > > > > > > >is one of the page faulted addresses?
> > > > > > Yes it's primary condition, due to there are could be another pages,
> > > > > > which weren't faulted, they just was sent from source to
> > > > > > destination,
> > > > > > I called it prefetching.
> > > > > >
> > > > > > I think I got why did you ask that question, because in this version
> > > > > > all_vcpu_down and as a result total_downtime calculated incorrectly,
> > > > > > it calculates every time when any page is copied, but it should
> > > > > > be calculated only when faulted page copied, so only
> > > > > > dc->vcpu_downtime
> > > > > > was correctly calculated.
> > > > >
> > > > > Exactly. I am afraid if we have such "prefetching" stuff then
> > > > > total_downtime will be more than its real value.
> > > >
> > > > It should be OK as long as we measure the time between
> > > > userfault reporting a page miss for an address
> > > > and
> > > > place_page for *that same address*
> > > >
> > > > any places for other pages are irrelevant.
> > > >
> > > > (I still worry that this definition of 'downtime' is possibly
> > > > arbitrary - since if all but one of the vCPUs are down we
> > > > don't count it but it's obviously still a big impact).
> > > Technically we count downtime per vCPU and storing it in
> > > vcpu_downtime field of PostcopyDowntimeContext (in this version
> > > still DowntimeContext). I traced downtime per vCPU in previous
> > > version.
> > > But it just traced as total_downtime in current version.
> > >
> > > Also total_downtime is not possible to get on destination, due to
> > > query-migrate is about MigrationState, but not MigrationIncomingState,
> > > so I think need to extend it to MigrationIncomingState too.
> >
> > I don't think that's too problematic; just add it to qmp_query_migrate;
> > the only thing to be careful of is what happens if the incoming
> > migration finishes during the info migrate is reading the
> > MigrationIncomingState.
> Do you mean none atomic read of s->state in qmp_query_migrate, if so
> it's also a pre-copy problem. I saw you atomic operations like
> postcopy_state_get/set.
Yes, you're right - I'd remembered that MigrationState was statically
allocated, I'd forgotten that MigrationIncomingState was also statically
allocated - so we don't have to worry about it getting freed.
Dave
> > Dave
> >
> > > >
> > > > Dave
> > > >
> > > > > --
> > > > > Peter Xu
> > > > --
> > > > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
> > > >
> > >
> > > --
> > >
> > > BR
> > > Alexey
> > --
> > Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
> >
>
> --
>
> BR
> Alexey
--
Dr. David Alan Gilbert / dgilb...@redhat.com / Manchester, UK
