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David Gibson 8904e5a750 spapr: Adjust default VSMT value for better migration compatibility
fa98fbfc "PC: KVM: Support machine option to set VSMT mode" introduced the
"vsmt" parameter for the pseries machine type, which controls the spacing
of the vcpu ids of thread 0 for each virtual core.  This was done to bring
some consistency and stability to how that was done, while still allowing
backwards compatibility for migration and otherwise.

The default value we used for vsmt was set to the max of the host's
advertised default number of threads and the number of vthreads per vcore
in the guest.  This was done to continue running without extra parameters
on older KVM versions which don't allow the VSMT value to be changed.

Unfortunately, even that smaller than before leakage of host configuration
into guest visible configuration still breaks things.  Specifically a guest
with 4 (or less) vthread/vcore will get a different vsmt value when
running on a POWER8 (vsmt==8) and POWER9 (vsmt==4) host.  That means the
vcpu ids don't line up so you can't migrate between them, though you should
be able to.

Long term we really want to make vsmt == smp_threads for sufficiently
new machine types.  However, that means that qemu will then require a
sufficiently recent KVM (one which supports changing VSMT) - that's still
not widely enough deployed to be really comfortable to do.

In the meantime we need some default that will work as often as
possible.  This patch changes that default to 8 in all circumstances.
This does change guest visible behaviour (including for existing
machine versions) for many cases - just not the most common/important
case.

Following is case by case justification for why this is still the least
worst option.  Note that any of the old behaviours can still be duplicated
after this patch, it's just that it requires manual intervention by
setting the vsmt property on the command line.

KVM HV on POWER8 host:
   This is the overwhelmingly common case in production setups, and is
   unchanged by design.  POWER8 hosts will advertise a default VSMT mode
   of 8, and > 8 vthreads/vcore isn't permitted

KVM HV on POWER7 host:
   Will break, but POWER7s allowing KVM were never released to the public.

KVM HV on POWER9 host:
   Not yet released to the public, breaking this now will reduce other
   breakage later.

KVM HV on PowerPC 970:
   Will theoretically break it, but it was barely supported to begin with
   and already required various user visible hacks to work.  Also so old
   that I just don't care.

TCG:
   This is the nastiest one; it means migration of TCG guests (without
   manual vsmt setting) will break.  Since TCG is rarely used in production
   I think this is worth it for the other benefits.  It does also remove
   one more barrier to TCG<->KVM migration which could be interesting for
   debugging applications.

KVM PR:
   As with TCG, this will break migration of existing configurations,
   without adding extra manual vsmt options.  As with TCG, it is rare in
   production so I think the benefits outweigh breakages.

Signed-off-by: David Gibson <david@gibson.dropbear.id.au>
Reviewed-by: Laurent Vivier <lvivier@redhat.com>
Reviewed-by: Jose Ricardo Ziviani <joserz@linux.vnet.ibm.com>
Reviewed-by: Greg Kurz <groug@kaod.org>
2018-01-17 09:35:24 +11:00
accel Queued TCG patches 2018-01-08 16:17:04 +00:00
audio maint: Fix macros with broken 'do/while(0); ' usage 2018-01-16 14:54:52 +01:00
backends tpm: tpm_emulator: get and set buffer size of device 2017-12-14 23:39:15 -05:00
block block/iscsi: fix initialization of iTask in iscsi_co_get_block_status 2018-01-16 14:54:52 +01:00
bsd-user misc: remove headers implicitly included 2017-12-18 17:07:02 +03:00
capstone@22ead3e0bf disas: Add capstone as submodule 2017-10-26 11:56:20 +02:00
chardev chardev: Clean up previous patch indentation 2018-01-16 14:54:52 +01:00
contrib contrib: add systemd unit files 2017-12-20 22:29:26 +01:00
crypto crypto: fix stack-buffer-overflow error 2018-01-16 14:54:50 +01:00
default-configs target-arm queue: 2018-01-11 14:34:41 +00:00
disas disas/s390: fix global-buffer-overflow 2018-01-16 14:54:50 +01:00
docs * QemuMutex tracing improvements (Alex) 2018-01-16 15:45:15 +00:00
dtc@e54388015a Update dtc to fix compilation problem on Mac OS 10.6 2018-01-10 12:53:00 +11:00
fpu
fsdev fsdev: improve error handling of backend init 2018-01-08 11:18:23 +01:00
gdb-xml
hw spapr: Adjust default VSMT value for better migration compatibility 2018-01-17 09:35:24 +11:00
include hw/ppc/spapr_caps: Rework spapr_caps to use uint8 internal representation 2018-01-17 09:35:24 +11:00
io io: introduce a network socket listener API 2017-12-15 15:07:26 +00:00
libdecnumber build: remove CONFIG_LIBDECNUMBER 2017-10-16 18:03:52 +02:00
linux-headers linux-headers: update to 4.15-rc1 2017-12-13 17:59:23 +00:00
linux-user linux-user/arm/nwfpe: Check coprocessor number for FPA emulation 2018-01-11 13:25:39 +00:00
migration * QemuMutex tracing improvements (Alex) 2018-01-16 15:45:15 +00:00
nbd nbd: rename nbd_option and nbd_opt_reply 2018-01-10 12:11:23 -06:00
net net: Remove the legacy "-net channel" parameter 2017-12-22 10:05:26 +08:00
pc-bios pseries: Update SLOF firmware image to qemu-slof-20171214 2018-01-10 12:52:59 +11:00
po
qapi migration: add postcopy total blocktime into query-migrate 2018-01-15 12:48:04 +01:00
qga sockets: remove obsolete code that updated listen address 2017-12-21 09:22:44 +01:00
qobject qapi: Add qobject_is_equal() 2017-11-17 18:21:30 +01:00
qom tcg: Add CPUState cflags_next_tb 2017-10-24 13:53:41 -07:00
replay
roms pseries: Update SLOF firmware image to qemu-slof-20171214 2018-01-10 12:52:59 +11:00
scripts * QemuMutex tracing improvements (Alex) 2018-01-16 15:45:15 +00:00
scsi scsi: fix scsi_convert_sense crash when in_buf == NULL && in_len == 0 2018-01-12 09:54:13 +01:00
slirp slirp: add in6_dhcp_multicast() 2018-01-14 18:16:13 +01:00
stubs tpm: add stubs 2017-10-25 01:05:04 -04:00
target target/ppc: Clarify compat mode max_threads value 2018-01-17 09:35:24 +11:00
tcg tcg/ppc: Allow a 32-bit offset to the constant pool 2018-01-16 08:21:56 -08:00
tests * QemuMutex tracing improvements (Alex) 2018-01-16 15:45:15 +00:00
trace trace: Try using tracefs first 2017-12-18 14:37:36 +00:00
ui * QemuMutex tracing improvements (Alex) 2018-01-16 15:45:15 +00:00
util util/qemu-thread-*: add qemu_lock, locked and unlock trace events 2018-01-16 14:54:52 +01:00
.dir-locals.el
.editorconfig
.exrc
.gdbinit
.gitignore .gitignore: remove vscclient 2017-12-18 17:07:02 +03:00
.gitmodules disas: Add capstone as submodule 2017-10-26 11:56:20 +02:00
.mailmap MAINTAINERS: Update Paul Burton's email address 2017-11-06 07:36:43 -08:00
.shippable.yml
.travis.yml
arch_init.c
balloon.c
block.c block: Keep nodes drained between reopen_queue/multiple 2017-12-22 15:05:32 +01:00
blockdev-nbd.c blockdev: convert internal NBD server to QIONetListener 2017-12-21 09:30:32 +01:00
blockdev.c block: Remove the obsolete -drive boot=on|off parameter 2017-12-22 15:03:41 +01:00
blockjob.c blockjob: Pause job on draining any job BDS 2017-12-22 15:05:32 +01:00
bootdevice.c
bt-host.c
bt-vhci.c
Changelog Use HTTPS for qemu.org and other domains 2017-11-21 13:34:13 +00:00
CODING_STYLE
configure * QemuMutex tracing improvements (Alex) 2018-01-16 15:45:15 +00:00
COPYING
COPYING.LIB
COPYING.PYTHON
cpus-common.c
cpus.c cpus: unify qemu_*_wait_io_event 2018-01-16 14:54:51 +01:00
device_tree.c
device-hotplug.c
disas.c disas: Dump insn bytes along with capstone disassembly 2017-11-09 08:46:38 +01:00
dma-helpers.c
dump.c dump: fix note_name_equal() 2018-01-02 14:49:54 +01:00
exec.c cpu: flush TB cache when loading VMState 2018-01-16 14:54:52 +01:00
gdbstub.c gdbstub: add tracing 2017-12-18 14:37:36 +00:00
HACKING
hmp-commands-info.hx
hmp-commands.hx hmp-commands: Remove the deprecated usb_add and usb_del 2017-12-14 10:16:52 +00:00
hmp.c migration: add postcopy total blocktime into query-migrate 2018-01-15 12:48:04 +01:00
hmp.h migrate: HMP migate_continue 2017-10-23 18:03:31 +02:00
ioport.c
iothread.c iothread: fix iothread_stop() race condition 2017-12-19 10:25:09 +00:00
LICENSE
MAINTAINERS ppc patch queue 2018-01-11 2018-01-11 13:24:17 +00:00
Makefile build-sys: add a rule to print a variable 2018-01-12 13:22:02 +01:00
Makefile.objs sparc64: introduce trace-events for hw/sparc64 2018-01-09 21:48:19 +00:00
Makefile.target Fix build of console and GUI executables for Windows 2017-11-23 10:46:42 +00:00
memory_ldst.inc.c
memory_mapping.c
memory.c memory: remove unused memory_region_set_global_locking() 2017-12-18 17:07:02 +03:00
module-common.c
monitor.c readline: add a free function 2018-01-16 14:54:50 +01:00
numa.c numa: remove unused #include 2017-12-18 17:07:02 +03:00
os-posix.c os-posix: Drop misleading comment 2017-10-16 21:01:37 +03:00
os-win32.c
qapi-schema.json qmp: remove qmp_cpu 2017-12-20 19:18:33 +01:00
qdev-monitor.c pci-assign: Remove 2017-11-05 14:52:10 +01:00
qdict-test-data.txt
qemu-bridge-helper.c
qemu-doc.texi ui: deprecate use of GTK 2.x in favour of 3.x series 2018-01-12 14:30:34 +01:00
qemu-ga.texi
qemu-img-cmds.hx
qemu-img.c block: Add errp to bdrv_snapshot_goto() 2017-11-21 14:48:22 +01:00
qemu-img.texi qemu-img.1: Image invalidation on qemu-img commit 2017-10-26 14:59:18 +02:00
qemu-io-cmds.c block: Keep nodes drained between reopen_queue/multiple 2017-12-22 15:05:32 +01:00
qemu-io.c
qemu-keymap.c
qemu-nbd.c blockdev: convert qemu-nbd server to QIONetListener 2017-12-21 09:30:32 +01:00
qemu-nbd.texi
qemu-option-trace.texi
qemu-options-wrapper.h qemu-options: Remove stray colons from output of --help 2017-12-20 09:04:27 +01:00
qemu-options.h
qemu-options.hx Block layer patches 2018-01-08 13:44:01 +00:00
qemu-seccomp.c
qemu-tech.texi
qemu.nsi Use HTTPS for qemu.org and other domains 2017-11-21 13:34:13 +00:00
qemu.sasl
qmp.c qmp: remove qmp_cpu 2017-12-20 19:18:33 +01:00
qtest.c
README Use HTTPS for qemu.org and other domains 2017-11-21 13:34:13 +00:00
replication.c
replication.h
rules.mak build-sys: silence make by default or V=0 2018-01-12 13:22:02 +01:00
thunk.c
tpm.c tpm: remove tpm_register_model() 2017-12-14 23:39:15 -05:00
trace-events find_ram_offset: Add comments and tracing 2018-01-16 14:54:52 +01:00
VERSION Open 2.12 development tree 2017-12-13 17:05:59 +00:00
version.rc Use HTTPS for qemu.org and other domains 2017-11-21 13:34:13 +00:00
vl.c * QemuMutex tracing improvements (Alex) 2018-01-16 15:45:15 +00:00

         QEMU README
         ===========

QEMU is a generic and open source machine & userspace emulator and
virtualizer.

QEMU is capable of emulating a complete machine in software without any
need for hardware virtualization support. By using dynamic translation,
it achieves very good performance. QEMU can also integrate with the Xen
and KVM hypervisors to provide emulated hardware while allowing the
hypervisor to manage the CPU. With hypervisor support, QEMU can achieve
near native performance for CPUs. When QEMU emulates CPUs directly it is
capable of running operating systems made for one machine (e.g. an ARMv7
board) on a different machine (e.g. an x86_64 PC board).

QEMU is also capable of providing userspace API virtualization for Linux
and BSD kernel interfaces. This allows binaries compiled against one
architecture ABI (e.g. the Linux PPC64 ABI) to be run on a host using a
different architecture ABI (e.g. the Linux x86_64 ABI). This does not
involve any hardware emulation, simply CPU and syscall emulation.

QEMU aims to fit into a variety of use cases. It can be invoked directly
by users wishing to have full control over its behaviour and settings.
It also aims to facilitate integration into higher level management
layers, by providing a stable command line interface and monitor API.
It is commonly invoked indirectly via the libvirt library when using
open source applications such as oVirt, OpenStack and virt-manager.

QEMU as a whole is released under the GNU General Public License,
version 2. For full licensing details, consult the LICENSE file.


Building
========

QEMU is multi-platform software intended to be buildable on all modern
Linux platforms, OS-X, Win32 (via the Mingw64 toolchain) and a variety
of other UNIX targets. The simple steps to build QEMU are:

  mkdir build
  cd build
  ../configure
  make

Additional information can also be found online via the QEMU website:

  https://qemu.org/Hosts/Linux
  https://qemu.org/Hosts/Mac
  https://qemu.org/Hosts/W32


Submitting patches
==================

The QEMU source code is maintained under the GIT version control system.

   git clone git://git.qemu.org/qemu.git

When submitting patches, the preferred approach is to use 'git
format-patch' and/or 'git send-email' to format & send the mail to the
qemu-devel@nongnu.org mailing list. All patches submitted must contain
a 'Signed-off-by' line from the author. Patches should follow the
guidelines set out in the HACKING and CODING_STYLE files.

Additional information on submitting patches can be found online via
the QEMU website

  https://qemu.org/Contribute/SubmitAPatch
  https://qemu.org/Contribute/TrivialPatches


Bug reporting
=============

The QEMU project uses Launchpad as its primary upstream bug tracker. Bugs
found when running code built from QEMU git or upstream released sources
should be reported via:

  https://bugs.launchpad.net/qemu/

If using QEMU via an operating system vendor pre-built binary package, it
is preferable to report bugs to the vendor's own bug tracker first. If
the bug is also known to affect latest upstream code, it can also be
reported via launchpad.

For additional information on bug reporting consult:

  https://qemu.org/Contribute/ReportABug


Contact
=======

The QEMU community can be contacted in a number of ways, with the two
main methods being email and IRC

 - qemu-devel@nongnu.org
   https://lists.nongnu.org/mailman/listinfo/qemu-devel
 - #qemu on irc.oftc.net

Information on additional methods of contacting the community can be
found online via the QEMU website:

  https://qemu.org/Contribute/StartHere

-- End