* [Qemu-devel] [PATCH v8 1/2] vl.c deprecate incorrect CPUs topology
2018-09-13 11:06 [Qemu-devel] [PATCH v8 0/2] deprecate incorrect CPUs topolog Igor Mammedov
@ 2018-09-13 11:06 ` Igor Mammedov
2018-09-13 14:58 ` Eric Blake
2018-09-13 11:06 ` [Qemu-devel] [PATCH v8 2/2] vl:c: make sure that sockets are calculated correctly in '-smp X' case Igor Mammedov
2018-10-08 14:42 ` [Qemu-devel] [PATCH v8 0/2] deprecate incorrect CPUs topolog Eduardo Habkost
2 siblings, 1 reply; 5+ messages in thread
From: Igor Mammedov @ 2018-09-13 11:06 UTC (permalink / raw)
To: qemu-devel; +Cc: eblake, ehabkost
-smp [cpus],sockets/cores/threads[,maxcpus] should describe topology
so that total number of logical CPUs [sockets * cores * threads]
would be equal to [maxcpus], however historically we didn't have
such check in QEMU and it is possible to start VM with an invalid
topology.
Deprecate invalid options combination so we can make sure that
the topology VM started with is always correct in the future.
Users with an invalid sockets/cores/threads/maxcpus values should
fix their CLI to make sure that
[sockets * cores * threads] == [maxcpus]
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
Reviewed-by: Eduardo Habkost <ehabkost@redhat.com>
---
V8:
- drop repetitive sentence:
"In other words: ..."
(Eric Blake <eblake@redhat.com>)
v7:
- add corrections to deprication doc formulas/math/section title
- drop Note section
(Eduardo Habkost <ehabkost@redhat.com>)
v6:
- s/socket/sockets/, the same for core, thread in subsection
(Andrew Jones <drjones@redhat.com>)
v5:
- extend deprecation doc, adding that maxcpus should be multiple of
present on CLI [sockets/cores/threads] options
(Eduardo Habkost <ehabkost@redhat.com>)
v4:
- missed dot comment, fix it with s/./,/ (Andrew Jones <drjones@redhat.com>)
v3:
- more spelling fixes (Andrew Jones <drjones@redhat.com>)
- place deprecation check after (sockets * cores * threads > max_cpus) check
(Eduardo Habkost <ehabkost@redhat.com>)
v2:
- spelling&&co fixes (Andrew Jones <drjones@redhat.com>)
---
qemu-deprecated.texi | 12 ++++++++++++
vl.c | 7 +++++++
2 files changed, 19 insertions(+)
diff --git a/qemu-deprecated.texi b/qemu-deprecated.texi
index 1b9c007..df717df 100644
--- a/qemu-deprecated.texi
+++ b/qemu-deprecated.texi
@@ -139,6 +139,18 @@ The 'file' driver for drives is no longer appropriate for character or host
devices and will only accept regular files (S_IFREG). The correct driver
for these file types is 'host_cdrom' or 'host_device' as appropriate.
+@subsection -smp (invalid topologies) (since 3.1)
+
+CPU topology properties should describe whole machine topology including
+possible CPUs.
+
+However, historically it was possible to start QEMU with an incorrect topology
+where @math{@var{n} <= @var{sockets} * @var{cores} * @var{threads} < @var{maxcpus}},
+which could lead to an incorrect topology enumeration by the guest.
+Support for invalid topologies will be removed, the user must ensure
+topologies described with -smp include all possible cpus, i.e.
+ @math{@var{sockets} * @var{cores} * @var{threads} = @var{maxcpus}}.
+
@section QEMU Machine Protocol (QMP) commands
@subsection block-dirty-bitmap-add "autoload" parameter (since 2.12.0)
diff --git a/vl.c b/vl.c
index 5ba06ad..7fd700e 100644
--- a/vl.c
+++ b/vl.c
@@ -1246,6 +1246,13 @@ static void smp_parse(QemuOpts *opts)
exit(1);
}
+ if (sockets * cores * threads != max_cpus) {
+ warn_report("Invalid CPU topology deprecated: "
+ "sockets (%u) * cores (%u) * threads (%u) "
+ "!= maxcpus (%u)",
+ sockets, cores, threads, max_cpus);
+ }
+
smp_cpus = cpus;
smp_cores = cores;
smp_threads = threads;
--
2.7.4
^ permalink raw reply related [flat|nested] 5+ messages in thread* [Qemu-devel] [PATCH v8 2/2] vl:c: make sure that sockets are calculated correctly in '-smp X' case
2018-09-13 11:06 [Qemu-devel] [PATCH v8 0/2] deprecate incorrect CPUs topolog Igor Mammedov
2018-09-13 11:06 ` [Qemu-devel] [PATCH v8 1/2] vl.c deprecate incorrect CPUs topology Igor Mammedov
@ 2018-09-13 11:06 ` Igor Mammedov
2018-10-08 14:42 ` [Qemu-devel] [PATCH v8 0/2] deprecate incorrect CPUs topolog Eduardo Habkost
2 siblings, 0 replies; 5+ messages in thread
From: Igor Mammedov @ 2018-09-13 11:06 UTC (permalink / raw)
To: qemu-devel; +Cc: eblake, ehabkost
commit
(5cdc9b76e3 vl.c: Remove dead assignment)
removed sockets calculation when 'sockets' weren't provided on CLI
since there wasn't any users for it back then. Exiting checks
are neither reachable
} else if (sockets * cores * threads < cpus) {
or nor triggerable
if (sockets * cores * threads > max_cpus)
so we weren't noticing wrong topology since then, since users
recalculate sockets adhoc on their own.
However with deprecation check it becomes noticable, for example
-smp 2
will start printing warning:
"warning: Invalid CPU topology deprecated: sockets (1) * cores (1) * threads (1) != maxcpus (2)"
calculating sockets if they weren't specified.
Fix it by returning back sockets calculation if it's omitted on CLI.
Signed-off-by: Igor Mammedov <imammedo@redhat.com>
Reviewed-by: Andrew Jones <drjones@redhat.com>
---
v8:
- spelling fixes in commit message (Eric Blake <eblake@redhat.com>)
---
vl.c | 5 ++++-
1 file changed, 4 insertions(+), 1 deletion(-)
diff --git a/vl.c b/vl.c
index 7fd700e..9e56696 100644
--- a/vl.c
+++ b/vl.c
@@ -1210,11 +1210,14 @@ static void smp_parse(QemuOpts *opts)
/* compute missing values, prefer sockets over cores over threads */
if (cpus == 0 || sockets == 0) {
- sockets = sockets > 0 ? sockets : 1;
cores = cores > 0 ? cores : 1;
threads = threads > 0 ? threads : 1;
if (cpus == 0) {
+ sockets = sockets > 0 ? sockets : 1;
cpus = cores * threads * sockets;
+ } else {
+ max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
+ sockets = max_cpus / (cores * threads);
}
} else if (cores == 0) {
threads = threads > 0 ? threads : 1;
--
2.7.4
^ permalink raw reply related [flat|nested] 5+ messages in thread