qemu/qapi
David Hildenbrand e2de2c497e util: Introduce ThreadContext user-creatable object
Setting the CPU affinity of QEMU threads is a bit problematic, because
QEMU doesn't always have permissions to set the CPU affinity itself,
for example, with seccomp after initialized by QEMU:
    -sandbox enable=on,resourcecontrol=deny

General information about CPU affinities can be found in the man page of
taskset:
    CPU affinity is a scheduler property that "bonds" a process to a given
    set of CPUs on the system. The Linux scheduler will honor the given CPU
    affinity and the process will not run on any other CPUs.

While upper layers are already aware of how to handle CPU affinities for
long-lived threads like iothreads or vcpu threads, especially short-lived
threads, as used for memory-backend preallocation, are more involved to
handle. These threads are created on demand and upper layers are not even
able to identify and configure them.

Introduce the concept of a ThreadContext, that is essentially a thread
used for creating new threads. All threads created via that context
thread inherit the configured CPU affinity. Consequently, it's
sufficient to create a ThreadContext and configure it once, and have all
threads created via that ThreadContext inherit the same CPU affinity.

The CPU affinity of a ThreadContext can be configured two ways:

(1) Obtaining the thread id via the "thread-id" property and setting the
    CPU affinity manually (e.g., via taskset).

(2) Setting the "cpu-affinity" property and letting QEMU try set the
    CPU affinity itself. This will fail if QEMU doesn't have permissions
    to do so anymore after seccomp was initialized.

A simple QEMU example to set the CPU affinity to host CPU 0,1,6,7 would be:
    qemu-system-x86_64 -S \
      -object thread-context,id=tc1,cpu-affinity=0-1,cpu-affinity=6-7

And we can query it via HMP/QMP:
    (qemu) qom-get tc1 cpu-affinity
    [
        0,
        1,
        6,
        7
    ]

But note that due to dynamic library loading this example will not work
before we actually make use of thread_context_create_thread() in QEMU
code, because the type will otherwise not get registered. We'll wire
this up next to make it work.

In general, the interface behaves like pthread_setaffinity_np(): host
CPU numbers that are currently not available are ignored; only host CPU
numbers that are impossible with the current kernel will fail. If the
list of host CPU numbers does not include a single CPU that is
available, setting the CPU affinity will fail.

A ThreadContext can be reused, simply by reconfiguring the CPU affinity.
Note that the CPU affinity of previously created threads will not get
adjusted.

Reviewed-by: Michal Privoznik <mprivozn@redhat.com>
Acked-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20221014134720.168738-4-david@redhat.com>
Signed-off-by: David Hildenbrand <david@redhat.com>
2022-10-27 11:00:43 +02:00
..
acpi.json qapi: fix example of ACPI_DEVICE_OST event 2022-03-31 12:35:59 +02:00
audio.json audio: Add sndio backend 2022-09-27 07:32:31 +02:00
authz.json qapi/qom: Add ObjectOptions for authz-* 2021-03-19 10:17:13 +01:00
block-core.json Revert "qapi: fix examples of blockdev-add with qcow2" 2022-10-07 12:11:40 +02:00
block-export.json vduse-blk: Add name option 2022-06-24 17:07:06 +02:00
block.json block: add more commands to preconfig mode 2022-06-14 16:50:30 +02:00
char.json qapi: Stop using whitespace for alignment in comments 2022-05-16 07:26:25 +02:00
common.json qapi: Drop unnecessary empty lines in comments 2022-05-16 07:22:28 +02:00
compat.json qapi: Belatedly adjust limitations documentation 2022-02-28 11:39:35 +01:00
control.json qapi: Stop using whitespace for alignment in comments 2022-05-16 07:26:25 +02:00
crypto.json qapi: crypto-akcipher: Introduce akcipher types to qapi 2022-05-26 11:41:42 +01:00
dump.json qapi: fix example of query-dump-guest-memory-capability command 2022-09-07 15:10:13 +02:00
error.json schemas: Add vim modeline 2020-08-03 08:28:08 +02:00
introspect.json qapi: Add feature flags to enum members 2021-10-27 17:18:55 +02:00
job.json qapi: Drop unnecessary empty lines outside of comments 2022-05-16 07:22:28 +02:00
machine-target.json target/loongarch: Implement qmp_query_cpu_definitions() 2022-06-06 18:09:03 +00:00
machine.json qmp/hmp, device_tree.c: introduce dumpdtb 2022-10-17 16:15:10 -03:00
meson.build qmp: add QMP command x-query-virtio 2022-10-09 16:38:45 -04:00
migration.json qapi: fix examples of events missing timestamp 2022-09-07 15:10:13 +02:00
misc-target.json qapi: Drop unnecessary whitespace in comments 2022-05-16 07:22:28 +02:00
misc.json vfio-user: run vfio-user context 2022-06-15 16:43:42 +01:00
net.json qapi: fix example of NIC_RX_FILTER_CHANGED event 2022-09-07 15:10:13 +02:00
opts-visitor.c qapi, qemu-options: make all parsing visitors parse boolean options the same 2020-11-04 12:00:40 -05:00
pci.json qapi: Normalize version references x.y.0 to just x.y 2020-12-10 17:16:44 +01:00
pragma.json qapi/pragma: Tidy up comments 2022-05-16 07:31:26 +02:00
qapi-clone-visitor.c qapi: Make visitor functions taking Error ** return bool, not void 2020-07-10 15:18:08 +02:00
qapi-dealloc-visitor.c qapi: Make visitor functions taking Error ** return bool, not void 2020-07-10 15:18:08 +02:00
qapi-forward-visitor.c qapi: remove needless include 2022-03-22 14:46:18 +04:00
qapi-schema.json qmp: add QMP command x-query-virtio 2022-10-09 16:38:45 -04:00
qapi-type-helpers.c monitor: introduce HumanReadableText and HMP support 2021-11-02 15:55:13 +00:00
qapi-util.c qapi: Fix stale reference to scripts/qapi.py in a comment 2022-02-28 11:39:35 +01:00
qapi-visit-core.c qapi: Factor out compat_policy_input_ok() 2021-10-29 21:27:20 +02:00
qdev.json qapi: fix example of DEVICE_UNPLUG_GUEST_ERROR event 2022-09-07 15:10:13 +02:00
qmp-dispatch.c qapi: remove needless include 2022-03-22 14:46:17 +04:00
qmp-event.c Replace qemu_gettimeofday() with g_get_real_time() 2022-04-06 10:50:37 +02:00
qmp-registry.c qapi: Generalize command policy checking 2021-10-29 18:24:46 +02:00
qobject-input-visitor.c include: add qemu/keyval.h 2022-04-21 17:03:51 +04:00
qobject-output-visitor.c qapi: Extend -compat to set policy for unstable interfaces 2021-10-29 21:28:01 +02:00
qom.json util: Introduce ThreadContext user-creatable object 2022-10-27 11:00:43 +02:00
rdma.json schemas: Add vim modeline 2020-08-03 08:28:08 +02:00
replay.json qapi: Drop unnecessary empty lines in comments 2022-05-16 07:22:28 +02:00
rocker.json schemas: Add vim modeline 2020-08-03 08:28:08 +02:00
run-state.json i386: add notify VM exit support 2022-10-11 09:36:00 +02:00
sockets.json qapi: Stop using whitespace for alignment in comments 2022-05-16 07:26:25 +02:00
stats.json monitor: add support for boolean statistics 2022-07-18 18:51:17 +02:00
string-input-visitor.c qapi, qemu-options: make all parsing visitors parse boolean options the same 2020-11-04 12:00:40 -05:00
string-output-visitor.c qapi: remove needless include 2022-03-22 14:46:18 +04:00
tpm.json qapi: Convert simple union TpmTypeOptions to flat one 2021-09-27 08:22:25 +02:00
trace-events qapi: Generalize struct member policy checking 2021-10-29 18:23:09 +02:00
trace.h trace: switch position of headers to what Meson requires 2020-08-21 06:18:24 -04:00
trace.json qapi: fix example of trace-event-get-state command 2022-04-05 12:30:45 +02:00
transaction.json qapi: deprecate drive-backup 2021-11-09 18:21:19 +01:00
ui.json gtk: Add show_menubar=on|off command line option. 2022-10-12 14:33:54 +02:00
virtio.json qmp: add QMP command x-query-virtio-queue-element 2022-10-09 16:38:45 -04:00
yank.json Introduce yank feature 2021-01-13 10:21:17 +01:00