On Wed, 29 Aug 2018 14:33:01 -0300
Eduardo Habkost <ehabk...@redhat.com> wrote:
> On Wed, Aug 29, 2018 at 04:32:01PM +0200, Igor Mammedov wrote:
> > 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 triggable
> > 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 omited on CLI.
> >
> > Signed-off-by: Igor Mammedov <imamm...@redhat.com>
> > ---
> > vl.c | 5 ++++-
> > 1 file changed, 4 insertions(+), 1 deletion(-)
> >
> > diff --git a/vl.c b/vl.c
> > index 7fd700e..333d638 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);
>
> We already have a "max_cpus = qemu_opt_get_number(...)" line in
> this function[1]:
>
> /* 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) {
> cpus = cores * threads * sockets;
> }
> } else if (cores == 0) {
> [...]
> } else if (threads == 0) {
> [...]
> } else if (sockets * cores * threads < cpus) {
> [...]
> }
>
> max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus); /* [1] */
>
> /* [2] */
>
> if (max_cpus < cpus) {
> error_report("maxcpus must be equal to or greater than smp");
> exit(1);
> }
>
> Why not move the sockets == 0 check to [2]?
it won't work, since the rest 'else if' depends on sockets being non 0
which is ensured by (cpus == 0 || sockets == 0) branch, I can split this in 2
equivalent conditions. It's more code but it might be easier to read
diff --git a/vl.c b/vl.c
index 7fd700e..6320bdc 100644
--- a/vl.c
+++ b/vl.c
@@ -1208,14 +1208,18 @@ static void smp_parse(QemuOpts *opts)
unsigned cores = qemu_opt_get_number(opts, "cores", 0);
unsigned threads = qemu_opt_get_number(opts, "threads", 0);
+ max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
/* compute missing values, prefer sockets over cores over threads */
- if (cpus == 0 || sockets == 0) {
+ if (cpus == 0) {
sockets = sockets > 0 ? sockets : 1;
cores = cores > 0 ? cores : 1;
threads = threads > 0 ? threads : 1;
- if (cpus == 0) {
- cpus = cores * threads * sockets;
- }
+ cpus = cores * threads * sockets;
+ max_cpus = max_cpus > 0 ? max_cpus : cpus;
+ } else if (sockets == 0) {
+ cores = cores > 0 ? cores : 1;
+ threads = threads > 0 ? threads : 1;
+ sockets = max_cpus / (cores * threads);
} else if (cores == 0) {
threads = threads > 0 ? threads : 1;
cores = cpus / (sockets * threads);
@@ -1231,8 +1235,6 @@ static void smp_parse(QemuOpts *opts)
exit(1);
}
- max_cpus = qemu_opt_get_number(opts, "maxcpus", cpus);
-
if (max_cpus < cpus) {
error_report("maxcpus must be equal to or greater than smp");
exit(1);
>
>
> > + sockets = !sockets ? max_cpus / (cores * threads) :
> > sockets;
>
> The two patches in this thread make QEMU print a warning on a
> case that was never documented as invalid/deprecated: maxcpus now
> needs to be a multiple of cores*threads.
>
> However, the error message doesn't make it obvious:
>
> $ ./x86_64-softmmu/qemu-system-x86_64 -smp 7,cores=3
> qemu-system-x86_64: warning: Invalid CPU topology deprecated: sockets (2) *
> cores (3) * threads (1) != maxcpus (7)
to me it look pretty obvious, fix one side of equation to make sure that VM
starts in the future.
> I think this would make more sense:
>
> $ ./x86_64-softmmu/qemu-system-x86_64 -smp 7,cores=3
> qemu-system-x86_64: warning: Invalid CPU topology deprecated: maxcpus (7)
> is not a multiple of cores (3) * threads (1)
I think it will add not necessary warning/code, but if you really
think we need it, I can add it to 'vl.c deprecate incorrect CPUs
topology' on respin.
>
>
> > }
> > } else if (cores == 0) {
> > threads = threads > 0 ? threads : 1;
> > --
> > 2.7.4
> >
>
