The round-robin scheduler will iterate over the CPU list with an
assigned budget until the next timer expiry and may exit early because
of a TB exit. This is fine under normal operation but with icount
enabled and SMP it is possible for a CPU to be starved of run time and
the system live-locks.
For example, booting a riscv64 platform with '-icount
shift=0,align=off,sleep=on -smp 2' we observe a livelock once the kernel
has timers enabled and starts performing TLB shootdowns. In this case
we have CPU 0 in M-mode with interrupts disabled sending an IPI to CPU
1. As we enter the TCG loop, we assign the icount budget to next timer
interrupt to CPU 0 and begin executing where the guest is sat in a busy
loop exhausting all of the budget before we try to execute CPU 1 which
is the target of the IPI but CPU 1 is left with no budget with which to
execute and the process repeats.
We try here to add some fairness by splitting the budget across all of
the CPUs on the thread fairly before entering each one. The CPU count
is cached on CPU list generation ID to avoid iterating the list on each
loop iteration. With this change it is possible to boot an SMP rv64
guest with icount enabled and no hangs.
Reviewed-by: Philippe Mathieu-Daudé <philmd@linaro.org>
Tested-by: Peter Maydell <peter.maydell@linaro.org>
Signed-off-by: Jamie Iles <quic_jiles@quicinc.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <20230427020925.51003-3-quic_jiles@quicinc.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
The function icount_prepare_for_run() is called with the iothread
unlocked, but it can call icount_notify_aio_contexts() which will
run qemu timer handlers. Those are supposed to be run only with
the iothread lock held, so take the lock while we do that.
Since icount mode runs everything on a single thread anyway,
not holding the lock is likely mostly not going to introduce
races, but it can cause us to trip over assertions that we
do hold the lock, such as the one reported in issue 1130.
Resolves: https://gitlab.com/qemu-project/qemu/-/issues/1130
Signed-off-by: Peter Maydell <peter.maydell@linaro.org>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Tested-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Message-id: 20220801164527.3134765-1-peter.maydell@linaro.org
This patch decouples checkpoints and async events.
It was a tricky part of replay implementation. Now it becomes
much simpler and easier to maintain.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Acked-by: Richard Henderson <richard.henderson@linaro.org>
Message-Id: <165364837856.688121.8785039478408995979.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This header only defines the tcg_allowed variable and the tcg_enabled()
function - which are not required in many files that include this
header. Drop the #include statement there.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Reviewed-by: Markus Armbruster <armbru@redhat.com>
Message-Id: <20220315144107.1012530-1-thuth@redhat.com>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
Reviewed-by: Paolo Bonzini <pbonzini@redhat.com>
Reviewed-by: Richard Henderson <richard.henderson@linaro.org>
Signed-off-by: Philippe Mathieu-Daudé <f4bug@amsat.org>
Message-Id: <20220207075426.81934-18-f4bug@amsat.org>
Stop including hw/boards.h in files that don't need it.
Signed-off-by: Thomas Huth <thuth@redhat.com>
Message-Id: <20210416171314.2074665-3-thuth@redhat.com>
Signed-off-by: Laurent Vivier <laurent@vivier.eu>
Sometimes interrupt event comes at the same time with
the virtual timers. In this case replay tries to proceed
the timers, because deadline for them is zero.
This patch allows processing interrupts and exceptions
by entering the vCPU execution loop, when deadline is zero,
but checkpoint associated with virtual timers is not ready
to be replayed.
Signed-off-by: Pavel Dovgalyuk <Pavel.Dovgalyuk@ispras.ru>
Message-Id: <161216312794.2030770.1709657858900983160.stgit@pasha-ThinkPad-X280>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
This will allow us to centralize the registration of
the cpus.c module accelerator operations (in accel/accel-softmmu.c),
and trigger it automatically using object hierarchy lookup from the
new accel_init_interfaces() initialization step, depending just on
which accelerators are available in the code.
Rename all tcg-cpus.c, kvm-cpus.c, etc to tcg-accel-ops.c,
kvm-accel-ops.c, etc, matching the object type names.
Signed-off-by: Claudio Fontana <cfontana@suse.de>
Message-Id: <20210204163931.7358-18-cfontana@suse.de>
Signed-off-by: Richard Henderson <richard.henderson@linaro.org>
