mpstat: Fix missing sample after physically hotplugging vCPU

When a vCPU is physically hotplugged, mpstat with its option -H skips
one line of statistics:

$ ./mpstat -H -P ALL 5 5
Linux 5.4.17-2136.310.7.1.el8uek.x86_64 (localhost.localdomain) 10/10/2022 x86_64 (3 CPU)

10:11:22 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
10:11:27 AM all 0.07 0.00 0.07 0.00 0.07 0.00 0.00 0.00 0.00 99.80
10:11:27 AM 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
10:11:27 AM 1 0.20 0.00 0.20 0.00 0.20 0.00 0.00 0.00 0.00 99.40
10:11:27 AM 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00

10:11:27 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
10:11:32 AM all 0.00 0.00 0.07 0.00 0.07 0.00 0.00 0.00 0.00 99.87
10:11:32 AM 0 0.00 0.00 0.00 0.00 0.20 0.00 0.00 0.00 0.00 99.80
10:11:32 AM 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
10:11:32 AM 2 0.00 0.00 0.20 0.00 0.00 0.00 0.00 0.00 0.00 99.80
[ 1154.848226] CPU3 has been hot-added
[ 1154.862315] smpboot: Booting Node 0 Processor 3 APIC 0x3
[ 1154.863956] kvm-clock: cpu 3, msr adc010c1, secondary cpu clock
[ 1154.884436] KVM setup async PF for cpu 3
[ 1154.886055] kvm-stealtime: cpu 3, msr 13b9b2040
[ 1154.887657] Will online and init hotplugged CPU: 3

10:11:32 AM CPU %usr %nice %sys %iowait %irq %soft %steal %guest %gnice %idle
<<<<<<< No sample for 10:11:37 >>>>>>>
10:11:42 AM all 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
10:11:42 AM 0 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
10:11:42 AM 1 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
10:11:42 AM 2 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00
10:11:42 AM 3 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 0.00 100.00

This patch makes sure that we get a line of stats for every interval of
time, even when a vCPU is physically hotplugged.

Signed-off-by: Sebastien GODARD <sysstat@users.noreply.github.com>

diff --git a/mpstat.c b/mpstat.c
index ab478c56911fcbd552015b0e76c0239a4c39267c..79f04390282bbb98ca8c31988094166b9ae2bb24 100644 (file)
--- a/mpstat.c
+++ b/mpstat.c
@@ -176,10 +176,12 @@ void int_handler(int sig)
  * IN:
  * @nr_cpus    Number of CPUs. This is the real number of available CPUs + 1
  *             because we also have to allocate a structure for CPU 'all'.
- * @reset      Reset the memory only when set to TRUE.
+ * @pos                Indicate which structures should be initialized. When @pos is
+ *             non zero, it means that only the additional, newly allocated
+ *             structures should be initialized.
  ***************************************************************************
  */
-void salloc_mp_struct(int nr_cpus, int reset)
+void salloc_mp_struct(int nr_cpus, int pos)
 {
        int i;
 
@@ -245,14 +247,14 @@ void salloc_mp_struct(int nr_cpus, int reset)
                exit(4);
        }
 
-       if (reset == TRUE) {
-               for (i = 0; i < 3; i++) {
-                       memset(st_cpu[i], 0, STATS_CPU_SIZE * nr_cpus);
-                       memset(st_node[i], 0, STATS_CPU_SIZE * nr_cpus);
-                       memset(st_irq[i], 0, STATS_GLOBAL_IRQ_SIZE * nr_cpus);
-                       memset(st_irqcpu[i], 0, STATS_IRQCPU_SIZE * nr_cpus * irqcpu_nr);
-                       memset(st_softirqcpu[i], 0, STATS_IRQCPU_SIZE * nr_cpus * softirqcpu_nr);
-               }
+       for (i = 0; i < 3; i++) {
+               memset(st_cpu[i] + pos, 0, STATS_CPU_SIZE * (nr_cpus - pos));
+               memset(st_node[i] + pos, 0, STATS_CPU_SIZE * (nr_cpus - pos));
+               memset(st_irq[i] + pos, 0, STATS_GLOBAL_IRQ_SIZE * (nr_cpus - pos));
+               memset(st_irqcpu[i] + pos, 0, STATS_IRQCPU_SIZE * (nr_cpus - pos) * irqcpu_nr);
+               memset(st_softirqcpu[i] + pos, 0, STATS_IRQCPU_SIZE * (nr_cpus - pos) * softirqcpu_nr);
+       }
+       if (!pos) {
                memset(cpu_bitmap, 0, (nr_cpus >> 3) + 1);
                memset(node_bitmap, 0, (nr_cpus >> 3) + 1);
        }
@@ -2144,8 +2146,24 @@ int rw_mpstat_loop(int dis_hdr, int rows)
                if (count && USE_OPTION_H(flags)) {
                        /* Check if a vCPU has been physically hotplugged */
                        new_cpu_nr = get_cpu_nr(~0, TRUE);
-                       if (new_cpu_nr > cpu_nr)
-                               return new_cpu_nr;
+                       if (new_cpu_nr > cpu_nr) {
+
+                               /* Recalculate number of interrupts per processor */
+                               irqcpu_nr = get_irqcpu_nr(INTERRUPTS, NR_IRQS, new_cpu_nr) +
+                               NR_IRQCPU_PREALLOC;
+                               /* Recalculate number of soft interrupts per processor */
+                               softirqcpu_nr = get_irqcpu_nr(SOFTIRQS, NR_IRQS, new_cpu_nr) +
+                               NR_IRQCPU_PREALLOC;
+
+                               /* Reallocate cpu stats structures */
+                               salloc_mp_struct(new_cpu_nr + 1, cpu_nr + 1);
+
+                               /* Get NUMA node placement */
+                               node_nr = get_node_placement(new_cpu_nr, cpu_per_node, cpu2node);
+
+                               /* Update the highest processor number */
+                               cpu_nr = new_cpu_nr;
+                       }
                }
        }
        while (count);
@@ -2160,49 +2178,6 @@ int rw_mpstat_loop(int dis_hdr, int rows)
        return 0;
 }
 
-/*
- ***************************************************************************
- * Start mpstat loop until end of count or when a vCPU has been physically
- * hotplugged.
- *
- * IN:
- * @dis_hdr    Set to TRUE if the header line must always be printed.
- * @rows       Number of rows of screen.
- ***************************************************************************
- */
-void mpstat_loop(int dis_hdr, int rows)
-{
-       int new_cpu_nr = 1;
-
-       while (new_cpu_nr) {
-               /* Main loop for reading-writing stats */
-               new_cpu_nr = rw_mpstat_loop(dis_hdr, rows);
-
-               /* Handle vCPU physical hotplug */
-               if (new_cpu_nr) {
-                       /* Update the highest processor number */
-                       cpu_nr = new_cpu_nr;
-
-                       /* Recalculate number of interrupts per processor */
-                       irqcpu_nr = get_irqcpu_nr(INTERRUPTS, NR_IRQS, cpu_nr) +
-                                   NR_IRQCPU_PREALLOC;
-                       /* Recalculate number of soft interrupts per processor */
-                       softirqcpu_nr = get_irqcpu_nr(SOFTIRQS, NR_IRQS, cpu_nr) +
-                                       NR_IRQCPU_PREALLOC;
-
-                       /*
-                        * Reallocate cpu stats structs :
-                        * global, proc0, proc1, ..., proc$(prev_cpu_nr-1).
-                        * global, proc0, proc1, ..., proc$(prev_cpu_nr-1), ..., proc$(cpu_nr-1).
-                        */
-                       salloc_mp_struct(cpu_nr + 1, FALSE);
-
-                       /* Get NUMA node placement */
-                       node_nr = get_node_placement(cpu_nr, cpu_per_node, cpu2node);
-               }
-       }
-}
-
 /*
  ***************************************************************************
  * Main entry to the program
@@ -2241,7 +2216,7 @@ int main(int argc, char **argv)
         * cpu_nr: a value of 2 means there are 2 processors (0 and 1).
         * In this case, we have to allocate 3 structures: global, proc0 and proc1.
         */
-       salloc_mp_struct(cpu_nr + 1, TRUE);
+       salloc_mp_struct(cpu_nr + 1, 0);
 
        /* Get NUMA node placement */
        node_nr = get_node_placement(cpu_nr, cpu_per_node, cpu2node);
@@ -2466,7 +2441,7 @@ int main(int argc, char **argv)
                         DISPLAY_JSON_OUTPUT(flags));
 
        /* Main loop */
-       mpstat_loop(dis_hdr, rows);
+       rw_mpstat_loop(dis_hdr, rows);
 
        /* Free structures */
        sfree_mp_struct();