Re: [Xen-devel] "xl vcpu-set" not persistent across reboot?

[Wei Liu <wei.liu2@xxxxxxxxxx>]

On Fri, Jun 03, 2016 at 08:42:11AM -0600, Jan Beulich wrote:
> >>> On 03.06.16 at 15:41, <wei.liu2@xxxxxxxxxx> wrote:
> > On Fri, Jun 03, 2016 at 02:29:12AM -0600, Jan Beulich wrote:
> >> Ian, Wei,
> >> 
> >> is it intentional that rebooting a (HVM) guest after having altered its
> >> vCPU count will reset it back to the vCPU count it was originally
> >> started with? That doesn't seem very natural - if one hotplugs a CPU
> >> into a physical system and then reboots, that CPU will remain there.
> >> 
> > 
> > This is probably an oversight.
> > 
> > I've added this to my list of things to look at after the release.
> 
> Thanks!
> 

I got a patch ready.  But QEMU upstream refuses to start on the receiving end
with following error message:

qemu-system-i386: Unknown savevm section or instance 'cpu_common' 1
qemu-system-i386: load of migration failed: Invalid argument

With QEMU traditional HVM guest and PV guest, the guest works fine -- up
and running with all hot plugged cpus available.

So I think the relevant libxl information is transmitted but we also
need to fix QEMU upstream. But that's a separate issue.

Wei.

---8<---
From 790ff77c6307b341dec0b4cc5e2d394e42f82e7c Mon Sep 17 00:00:00 2001
From: Wei Liu <wei.liu2@xxxxxxxxxx>
Date: Fri, 3 Jun 2016 16:38:32 +0100
Subject: [PATCH] libxl: update vcpus bitmap in retrieved geust config

... because the available vcpu bitmap can change during domain life time
due to cpu hotplug and unplug.

Reported-by: Jan Beulich <jbeulich@xxxxxxxx>
Signed-off-by: Wei Liu <wei.liu2@xxxxxxxxxx>
---
 tools/libxl/libxl.c | 31 +++++++++++++++++++++++++++++++
 1 file changed, 31 insertions(+)

diff --git a/tools/libxl/libxl.c b/tools/libxl/libxl.c
index 006b83f..99617f3 100644
--- a/tools/libxl/libxl.c
+++ b/tools/libxl/libxl.c
@@ -7270,6 +7270,37 @@ int libxl_retrieve_domain_configuration(libxl_ctx *ctx, 
uint32_t domid,
         libxl_dominfo_dispose(&info);
     }
 
+    /* VCPUs */
+    {
+        libxl_vcpuinfo *vcpus;
+        libxl_bitmap *map;
+        int nr_vcpus, nr_cpus;
+        unsigned int i;
+
+        vcpus = libxl_list_vcpu(ctx, domid, &nr_vcpus, &nr_cpus);
+        if (!vcpus) {
+            LOG(ERROR, "fail to get vcpu list for domain %d", domid);
+            rc = ERROR_FAIL;
+            goto out;
+        }
+
+        /* Update the avail_vcpus bitmap accordingly */
+        map = &d_config->b_info.avail_vcpus;
+
+        libxl_bitmap_dispose(map);
+
+        libxl_bitmap_alloc(ctx, map, nr_vcpus);
+
+        libxl_bitmap_init(map);
+
+        for (i = 0; i < nr_vcpus; i++) {
+            if (vcpus[i].online)
+                libxl_bitmap_set(map, i);
+        }
+
+        libxl_vcpuinfo_list_free(vcpus, nr_vcpus);
+    }
+
     /* Memory limits:
      *
      * Currently there are three memory limits:
-- 
2.1.4



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