qemu/stubs/iothread-lock.c

#include "qemu/osdep.h"
#include "qemu/main-loop.h"

bool qemu_mutex_iothread_locked(void)
{
    return false;
}

void qemu_mutex_lock_iothread_impl(const char *file, int line)
{
}

void qemu_mutex_unlock_iothread(void)
{
}
stubs: Clean up includes Clean up includes so that osdep.h is included first and headers which it implies are not included manually. This commit was created with scripts/clean-includes. Signed-off-by: Peter Maydell <peter.maydell@linaro.org> Message-id: 1454089805-5470-3-git-send-email-peter.maydell@linaro.org 2016-01-30 01:49:52 +08:00			`#include "qemu/osdep.h"`
stubs: fully replace qemu-tool.c and qemu-user.c Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> 2012-11-26 22:36:40 +08:00			`#include "qemu/main-loop.h"`

main-loop: introduce qemu_mutex_iothread_locked This function will be used to avoid recursive locking of the iothread lock whenever address_space_rw/ld/st are called with the BQL held, which is almost always the case. Tracking whether the iothread is owned is very cheap (just use a TLS variable) but requires some care because now the lock must always be taken with qemu_mutex_lock_iothread(). Previously this wasn't the case. Outside TCG mode this is not a problem. In TCG mode, we need to be careful and avoid the "prod out of compiled code" step if already in a VCPU thread. This is easily done with a check on current_cpu, i.e. qemu_in_vcpu_thread(). Hopefully, multithreaded TCG will get rid of the whole logic to kick VCPUs whenever an I/O event occurs! Cc: Frederic Konrad <fred.konrad@greensocs.com> Message-Id: <1434646046-27150-3-git-send-email-pbonzini@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> 2015-06-19 00:47:19 +08:00			`bool qemu_mutex_iothread_locked(void)`
			`{`
async: the main AioContext is only "current" if under the BQL If we want to wake up a coroutine from a worker thread, aio_co_wake() currently does not work. In that scenario, aio_co_wake() calls aio_co_enter(), but there is no current AioContext and therefore qemu_get_current_aio_context() returns the main thread. aio_co_wake() then attempts to call aio_context_acquire() instead of going through aio_co_schedule(). The default case of qemu_get_current_aio_context() was added to cover synchronous I/O started from the vCPU thread, but the main and vCPU threads are quite different. The main thread is an I/O thread itself, only running a more complicated event loop; the vCPU thread instead is essentially a worker thread that occasionally calls qemu_mutex_lock_iothread(). It is only in those critical sections that it acts as if it were the home thread of the main AioContext. Therefore, this patch detaches qemu_get_current_aio_context() from iothreads, which is a useless complication. The AioContext pointer is stored directly in the thread-local variable, including for the main loop. Worker threads (including vCPU threads) optionally behave as temporary home threads if they have taken the big QEMU lock, but if that is not the case they will always schedule coroutines on remote threads via aio_co_schedule(). With this change, the stub qemu_mutex_iothread_locked() must be changed from true to false. The previous value of true was needed because the main thread did not have an AioContext in the thread-local variable, but now it does have one. Reported-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> Message-Id: <20210609122234.544153-1-pbonzini@redhat.com> Reviewed-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> Tested-by: Vladimir Sementsov-Ogievskiy <vsementsov@virtuozzo.com> [eblake: tweak commit message per Vladimir's review] Signed-off-by: Eric Blake <eblake@redhat.com> 2021-06-09 20:22:34 +08:00			`return false;`
main-loop: introduce qemu_mutex_iothread_locked This function will be used to avoid recursive locking of the iothread lock whenever address_space_rw/ld/st are called with the BQL held, which is almost always the case. Tracking whether the iothread is owned is very cheap (just use a TLS variable) but requires some care because now the lock must always be taken with qemu_mutex_lock_iothread(). Previously this wasn't the case. Outside TCG mode this is not a problem. In TCG mode, we need to be careful and avoid the "prod out of compiled code" step if already in a VCPU thread. This is easily done with a check on current_cpu, i.e. qemu_in_vcpu_thread(). Hopefully, multithreaded TCG will get rid of the whole logic to kick VCPUs whenever an I/O event occurs! Cc: Frederic Konrad <fred.konrad@greensocs.com> Message-Id: <1434646046-27150-3-git-send-email-pbonzini@redhat.com> Reviewed-by: Fam Zheng <famz@redhat.com> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> 2015-06-19 00:47:19 +08:00			`}`

qsp: track BQL callers explicitly The BQL is acquired via qemu_mutex_lock_iothread(), which makes the profiler assign the associated wait time (i.e. most of BQL wait time) entirely to that function. This loses the original call site information, which does not help diagnose BQL contention. Fix it by tracking the callers explicitly. Signed-off-by: Emilio G. Cota <cota@braap.org> Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> 2017-10-28 14:16:41 +08:00			`void qemu_mutex_lock_iothread_impl(const char *file, int line)`
stubs: fully replace qemu-tool.c and qemu-user.c Signed-off-by: Paolo Bonzini <pbonzini@redhat.com> 2012-11-26 22:36:40 +08:00			`{`
			`}`

			`void qemu_mutex_unlock_iothread(void)`
			`{`
			`}`