[PATCH v1] domctl: hold domctl lock while domain is destroyed

[Dmitry Isaikin <isaikin-dmitry@xxxxxxxxx>]

From: Dmitry Isaykin <isaikin-dmitry@xxxxxxxxx>

This significantly speeds up concurrent destruction of multiple domains on x86.

I identify the place taking the most time:

    do_domctl(case XEN_DOMCTL_destroydomain)
      -> domain_kill()
           -> domain_relinquish_resources()
                -> relinquish_memory(d, &d->page_list, PGT_l4_page_table)

My reference setup: Intel(R) Xeon(R) CPU E5-2680 v4 @ 2.40GHz, Xen 4.14.

I use this command for test:

    for i in $(seq 1 5) ; do xl destroy test-vm-${i} & done

Without holding the lock all calls of `relinquish_memory(d, &d->page_list, 
PGT_l4_page_table)`
took on my setup (for HVM with 2GB of memory) about 3 seconds for each 
destroying domain.

With holding the lock it took only 100 ms.

Signed-off-by: Dmitry Isaykin <isaikin-dmitry@xxxxxxxxx>
---
 xen/common/domctl.c | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)

diff --git a/xen/common/domctl.c b/xen/common/domctl.c
index 12d6144d28..b9a50d3e5d 100644
--- a/xen/common/domctl.c
+++ b/xen/common/domctl.c
@@ -497,14 +497,13 @@ long do_domctl(XEN_GUEST_HANDLE_PARAM(xen_domctl_t) 
u_domctl)
         break;
 
     case XEN_DOMCTL_destroydomain:
-        domctl_lock_release();
         domain_lock(d);
         ret = domain_kill(d);
         domain_unlock(d);
         if ( ret == -ERESTART )
             ret = hypercall_create_continuation(
                 __HYPERVISOR_domctl, "h", u_domctl);
-        goto domctl_out_unlock_domonly;
+        break;
 
     case XEN_DOMCTL_setnodeaffinity:
     {
-- 
2.33.0