On Wed, Aug 03, 2011 at 12:37:13PM +0200, Jan Kiszka wrote:
On 2011-08-03 12:07, Vasilis Liaskovitis wrote:
When rebooting after a CPU hotplug in qemu-kvm, Seabios can get stuck in smp_probe(). Normally cmos_smp_count is read from cmos and the smp_ap_boot_code is run on all cpus except bootstrap. The expected result is CountCPUs == cmos_smp_count + 1. After a cpu hotplug, more than cmos_smp_count cpus are active, so we get a situation where CountCPUs > cmos_smp_count + 1 and Seabios keeps looping forever in smp_probe. In some cases, the while loop exit condition is tested before CountCPUs gets larger (i.e. before smp_ap_boot_code runs on all CPUs), so the hang is not always reproducible.
This patch introduces a new fw_cfg variable called hotplugged_cpus that gets updated from qemu-kvm hoplug code. Seabios reads this variable on each call to smp_probe() and adjusts the expected number of online CPUs.
The qemu-kvm part of this patch is against Jan Kiszka's cpu-hotplug tree: git://git.kiszka.org/qemu-kvm.git queues/cpu-hotplug tested with qemu-system-x86_64.
An alternative to this patch would be to update the smp_cpus variable in qemu-kvm and do a "cmos update" to 0x5f from the cpu-hotplug code. Access to the rtc_state (cmos device) would be required in hw/acpi_piix4.c. This way no change to Seabios would be required.
...
src/paravirt.c | 12 ++++++++++++ src/paravirt.h | 2 ++ src/smp.c | 6 ++++-- 3 files changed, 18 insertions(+), 2 deletions(-)
diff --git a/src/paravirt.c b/src/paravirt.c index 9cf77de..3367609 100644 --- a/src/paravirt.c +++ b/src/paravirt.c @@ -305,6 +305,18 @@ u16 qemu_cfg_get_max_cpus(void) return cnt; }
+u16 qemu_cfg_get_hplug_cpus(void) +{
- u16 cnt;
- if (!qemu_cfg_present)
return 0;- qemu_cfg_read_entry(&cnt, QEMU_CFG_HPLUG_CPUS, sizeof(cnt));
Why can't Seabios read to true number online CPUs from the PIIX4 device? The information is there already, no need for addition PV here.
Where is it in PIIX4 device?
-- Gleb.