commit a098761f63e019b75a23575bb8d5a520c0dbce64
author Peter Xu <peterx@redhat.com> Fri Jun 13 10:12:09 2025 -0400
committer Fabiano Rosas <farosas@suse.de> Fri Jul 11 10:37:38 2025 -0300
tree acf6cac46bef27d4d62b9afe3b4a56fe636d8ded
parent 08fb2a933586183be788aac43c62b2993e0a99ce

migration/postcopy: Bring blocktime layer to ns level

With 64-bit fields, it is trivial.  The caution is when exposing any values
in QMP, it was still declared with milliseconds (ms).  Hence it's needed to
do the convertion when exporting the values to existing QMP queries.

Reviewed-by: Fabiano Rosas <farosas@suse.de>
Link: https://lore.kernel.org/r/20250613141217.474825-7-peterx@redhat.com
Signed-off-by: Peter Xu <peterx@redhat.com>
Signed-off-by: Fabiano Rosas <farosas@suse.de>

migration/postcopy-ram.c

diff --git a/migration/postcopy-ram.c b/migration/postcopy-ram.c
index e9acb4e..9dfa92a 100644
--- a/migration/postcopy-ram.c
+++ b/migration/postcopy-ram.c
@@ -110,6 +110,7 @@
 #include <sys/eventfd.h>
 #include <linux/userfaultfd.h>
 
+/* All the time records are in unit of nanoseconds */
 typedef struct PostcopyBlocktimeContext {
     /* time when page fault initiated per vCPU */
     uint64_t *vcpu_blocktime_start;
@@ -168,7 +169,9 @@
     int i;
 
     for (i = ms->smp.cpus - 1; i >= 0; i--) {
-        QAPI_LIST_PREPEND(list, (uint32_t)ctx->vcpu_blocktime_total[i]);
+        /* Convert ns -> ms */
+        QAPI_LIST_PREPEND(
+            list, (uint32_t)(ctx->vcpu_blocktime_total[i] / SCALE_MS));
     }
 
     return list;
@@ -191,7 +194,8 @@
     }
 
     info->has_postcopy_blocktime = true;
-    info->postcopy_blocktime = (uint32_t)bc->total_blocktime;
+    /* Convert ns -> ms */
+    info->postcopy_blocktime = (uint32_t)(bc->total_blocktime / SCALE_MS);
     info->has_postcopy_vcpu_blocktime = true;
     info->postcopy_vcpu_blocktime = get_vcpu_blocktime_list(bc);
 }
@@ -816,9 +820,9 @@
     return -1;
 }
 
-static uint64_t get_low_time_offset(void)
+static uint64_t get_current_ns(void)
 {
-    return (uint64_t)qemu_clock_get_ms(QEMU_CLOCK_REALTIME);
+    return (uint64_t)qemu_clock_get_ns(QEMU_CLOCK_REALTIME);
 }
 
 /*
@@ -835,7 +839,7 @@
     int cpu;
     MigrationIncomingState *mis = migration_incoming_get_current();
     PostcopyBlocktimeContext *dc = mis->blocktime_ctx;
-    uint64_t low_time_offset;
+    uint64_t current;
 
     if (!dc || ptid == 0) {
         return;
@@ -845,13 +849,13 @@
         return;
     }
 
-    low_time_offset = get_low_time_offset();
+    current = get_current_ns();
     if (dc->vcpu_addr[cpu] == 0) {
         dc->smp_cpus_down++;
     }
 
-    dc->last_begin = low_time_offset;
-    dc->vcpu_blocktime_start[cpu] = low_time_offset;
+    dc->last_begin = current;
+    dc->vcpu_blocktime_start[cpu] = current;
     dc->vcpu_addr[cpu] = addr;
 
     /*
@@ -899,13 +903,13 @@
     unsigned int smp_cpus = ms->smp.cpus;
     int i, affected_cpu = 0;
     bool vcpu_total_blocktime = false;
-    uint64_t read_vcpu_time, low_time_offset;
+    uint64_t read_vcpu_time, current;
 
     if (!dc) {
         return;
     }
 
-    low_time_offset = get_low_time_offset();
+    current = get_current_ns();
     /* lookup cpu, to clear it,
      * that algorithm looks straightforward, but it's not
      * optimal, more optimal algorithm is keeping tree or hash
@@ -918,7 +922,7 @@
             continue;
         }
         dc->vcpu_addr[i] = 0;
-        vcpu_blocktime = low_time_offset - read_vcpu_time;
+        vcpu_blocktime = current - read_vcpu_time;
         affected_cpu += 1;
         /* we need to know is that mark_postcopy_end was due to
          * faulted page, another possible case it's prefetched
@@ -932,7 +936,7 @@
 
     dc->smp_cpus_down -= affected_cpu;
     if (vcpu_total_blocktime) {
-        dc->total_blocktime += low_time_offset - dc->last_begin;
+        dc->total_blocktime += current - dc->last_begin;
     }
     trace_mark_postcopy_blocktime_end(addr, dc->total_blocktime,
                                       affected_cpu);