qemu-e2k/include/qemu/thread-context.h

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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>
2022-10-14 15:47:16 +02:00
/*
* QEMU Thread Context
*
* Copyright Red Hat Inc., 2022
*
* Authors:
* David Hildenbrand <david@redhat.com>
*
* This work is licensed under the terms of the GNU GPL, version 2 or later.
* See the COPYING file in the top-level directory.
*/
#ifndef SYSEMU_THREAD_CONTEXT_H
#define SYSEMU_THREAD_CONTEXT_H
#include "qapi/qapi-types-machine.h"
#include "qemu/thread.h"
#include "qom/object.h"
#define TYPE_THREAD_CONTEXT "thread-context"
OBJECT_DECLARE_TYPE(ThreadContext, ThreadContextClass,
THREAD_CONTEXT)
struct ThreadContextClass {
ObjectClass parent_class;
};
struct ThreadContext {
/* private */
Object parent;
/* private */
unsigned int thread_id;
QemuThread thread;
/* Semaphore to wait for context thread action. */
QemuSemaphore sem;
/* Semaphore to wait for action in context thread. */
QemuSemaphore sem_thread;
/* Mutex to synchronize requests. */
QemuMutex mutex;
/* Commands for the thread to execute. */
int thread_cmd;
void *thread_cmd_data;
/* CPU affinity bitmap used for initialization. */
unsigned long *init_cpu_bitmap;
int init_cpu_nbits;
};
void thread_context_create_thread(ThreadContext *tc, QemuThread *thread,
const char *name,
void *(*start_routine)(void *), void *arg,
int mode);
#endif /* SYSEMU_THREAD_CONTEXT_H */