From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:55649) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1bBQQH-0006JN-4a for qemu-devel@nongnu.org; Fri, 10 Jun 2016 13:40:51 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1bBQQF-0000MM-3p for qemu-devel@nongnu.org; Fri, 10 Jun 2016 13:40:44 -0400 From: Andrew Jones Date: Fri, 10 Jun 2016 19:40:13 +0200 Message-Id: <1465580427-13596-3-git-send-email-drjones@redhat.com> In-Reply-To: <1465580427-13596-1-git-send-email-drjones@redhat.com> References: <1465580427-13596-1-git-send-email-drjones@redhat.com> Subject: [Qemu-devel] [PATCH RFC 02/16] vl: smp: add checks for maxcpus based topologies List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: qemu-devel@nongnu.org, qemu-ppc@nongnu.org, qemu-arm@nongnu.org Cc: imammedo@redhat.com, ehabkost@redhat.com, pbonzini@redhat.com, peter.maydell@linaro.org, david@gibson.dropbear.id.au, dgibson@redhat.com, agraf@suse.de smp_parse computes missing smp options. Unfortunately cores and threads are computed by dividing smp_cpus, instead of max_cpus. This is incorrect because the topology doesn't leave room for hotplug. More unfortunately, we can't change it easily, as doing so would impact existing command lines. This patch adds a warning when the topology doesn't add up, and then checks that the topology at least computes when sockets are recalculated. If not, then it does fail. Adding the new failure is justified by the fact that we don't store the number of input sockets, and thus all consumers of cpu topology information recalculate it. If they choose to (correctly) calculate it based on maxcpus, then we need to guard them against building topologies which provide more cpu slots than are the maximum allowed cpus. Signed-off-by: Andrew Jones --- vl.c | 19 +++++++++++++++++++ 1 file changed, 19 insertions(+) diff --git a/vl.c b/vl.c index 7b96e787922f9..8d482cb1bf020 100644 --- a/vl.c +++ b/vl.c @@ -1227,6 +1227,7 @@ static void smp_parse(QemuOpts *opts) unsigned sockets = qemu_opt_get_number(opts, "sockets", 0); unsigned cores = qemu_opt_get_number(opts, "cores", 0); unsigned threads = qemu_opt_get_number(opts, "threads", 0); + bool sockets_input = sockets > 0; /* compute missing values, prefer sockets over cores over threads */ if (cpus == 0 || sockets == 0) { @@ -1269,6 +1270,24 @@ static void smp_parse(QemuOpts *opts) exit(1); } + if (sockets_input && sockets * cores * threads != max_cpus) { + unsigned sockets_rounded = DIV_ROUND_UP(max_cpus, cores * threads); + + error_report("warning: cpu topology: " + "sockets (%u) * cores (%u) * threads (%u) != " + "maxcpus (%u). Trying sockets=%u.", + sockets, cores, threads, max_cpus, sockets_rounded); + sockets = sockets_rounded; + + if (sockets * cores * threads > max_cpus) { + error_report("cpu topology: " + "sockets (%u) * cores (%u) * threads (%u) > " + "maxcpus (%u)", + sockets, cores, threads, max_cpus); + exit(1); + } + } + smp_cpus = cpus; smp_cores = cores; smp_threads = threads; -- 2.4.11