On Mon, May 13, 2024 at 01:33:57PM +0100, Daniel P. Berrangé wrote: > Date: Mon, 13 May 2024 13:33:57 +0100 > From: "Daniel P. Berrangé" <berrange@xxxxxxxxxx> > Subject: [PATCH 1/2] hw/core: allow parameter=1 for SMP topology on any > machine > > This effectively reverts > > commit 54c4ea8f3ae614054079395842128a856a73dbf9 > Author: Zhao Liu <zhao1.liu@xxxxxxxxx> > Date: Sat Mar 9 00:01:37 2024 +0800 > > hw/core/machine-smp: Deprecate unsupported "parameter=1" SMP configurations > > but is not done as a 'git revert' since the part of the changes to the > file hw/core/machine-smp.c which add 'has_XXX' checks remain desirable. > Furthermore, we have to tweak the subsequently added unit test to > account for differing warning message. > > The rationale for the original deprecation was: > > "Currently, it was allowed for users to specify the unsupported > topology parameter as "1". For example, x86 PC machine doesn't > support drawer/book/cluster topology levels, but user could specify > "-smp drawers=1,books=1,clusters=1". > > This is meaningless and confusing, so that the support for this kind > of configurations is marked deprecated since 9.0." > > There are varying POVs on the topic of 'unsupported' topology levels. > > It is common to say that on a system without hyperthreading, that there > is always 1 thread. Likewise when new CPUs introduced a concept of > multiple "dies', it was reasonable to say that all historical CPUs > before that implicitly had 1 'die'. Likewise for the more recently > introduced 'modules' and 'clusters' parameter'. From this POV, it is > valid to set 'parameter=1' on the -smp command line for any machine, > only a value > 1 is strictly an error condition. > > It doesn't cause any functional difficulty for QEMU, because internally > the QEMU code is itself assuming that all "unsupported" parameters > implicitly have a value of '1'. > > At the libvirt level, we've allowed applications to set 'parameter=1' > when configuring a guest, and pass that through to QEMU. > > Deprecating this creates extra difficulty for because there's no info > exposed from QEMU about which machine types "support" which parameters. > Thus, libvirt can't know whether it is valid to pass 'parameter=1' for > a given machine type, or whether it will trigger deprecation messages. > > Since there's no apparent functional benefit to deleting this deprecated > behaviour from QEMU, and it creates problems for consumers of QEMU, > remove this deprecation. > > Signed-off-by: Daniel P. Berrangé <berrange@xxxxxxxxxx> > --- > docs/about/deprecated.rst | 14 ------- > hw/core/machine-smp.c | 82 ++++++++++++------------------------- > tests/unit/test-smp-parse.c | 8 ++-- > 3 files changed, 30 insertions(+), 74 deletions(-) > > diff --git a/docs/about/deprecated.rst b/docs/about/deprecated.rst > index e22acb17f2..5b551b12a6 100644 > --- a/docs/about/deprecated.rst > +++ b/docs/about/deprecated.rst > @@ -47,20 +47,6 @@ as short-form boolean values, and passed to plugins as ``arg_name=on``. > However, short-form booleans are deprecated and full explicit ``arg_name=on`` > form is preferred. > > -``-smp`` (Unsupported "parameter=1" SMP configurations) (since 9.0) > -''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''''' > - > -Specified CPU topology parameters must be supported by the machine. > - > -In the SMP configuration, users should provide the CPU topology parameters that > -are supported by the target machine. > - > -However, historically it was allowed for users to specify the unsupported > -topology parameter as "1", which is meaningless. So support for this kind of > -configurations (e.g. -smp drawers=1,books=1,clusters=1 for x86 PC machine) is > -marked deprecated since 9.0, users have to ensure that all the topology members > -described with -smp are supported by the target machine. > - > User-mode emulator command line arguments > ----------------------------------------- > > diff --git a/hw/core/machine-smp.c b/hw/core/machine-smp.c > index 2b93fa99c9..eb43caca9b 100644 > --- a/hw/core/machine-smp.c > +++ b/hw/core/machine-smp.c > @@ -119,75 +119,45 @@ void machine_parse_smp_config(MachineState *ms, > > /* > * If not supported by the machine, a topology parameter must be Also need to change this line as: s/must be/must/ > - * omitted. > + * not be set to a value greater than 1. > */ Only the above nit, Reviewed-by: Zhao Liu <zhao1.liu@xxxxxxxxx>
