From: Igor Mammedov <imammedo@redhat.com>
To: "Alex Bennée" <alex.bennee@linaro.org>
Cc: Paolo Bonzini <pbonzini@redhat.com>,
Richard Henderson <rth@twiddle.net>,
qemu-devel@nongnu.org, Eduardo Habkost <ehabkost@redhat.com>,
Nikolay Igotti <igotti@gmail.com>
Subject: Re: [PATCH v1 5/8] cpus-common: ensure auto-assigned cpu_indexes don't clash
Date: Thu, 21 May 2020 17:53:03 +0200 [thread overview]
Message-ID: <20200521175303.74faabe2@redhat.com> (raw)
In-Reply-To: <87y2pucwhi.fsf@linaro.org>
On Thu, 14 May 2020 17:27:53 +0100
Alex Bennée <alex.bennee@linaro.org> wrote:
> a
> Alex Bennée <alex.bennee@linaro.org> writes:
>
> > Basing the cpu_index on the number of currently allocated vCPUs fails
> > when vCPUs aren't removed in a LIFO manner. This is especially true
> > when we are allocating a cpu_index for each guest thread in
> > linux-user where there is no ordering constraint on their allocation
> > and de-allocation.
> >
> > [I've dropped the assert which is there to guard against out-of-order
> > removal as this should probably be caught higher up the stack. Maybe
> > we could just ifdef CONFIG_SOFTTMU it?]
for machines where we care about cross version migration (arm/virt,s390,x86,spapr),
we do manual cpu_index assignment on keep control on its stability
So orderining probably shouldn't matter for other softmmu boards,
but what I'd watch for is arrays within devices where cpu_index is used as index
(ex: would be apic emulation (but its not affected by this patch since x86 control
cpu_index assignment))
> >
> > Signed-off-by: Alex Bennée <alex.bennee@linaro.org>
> > Cc: Nikolay Igotti <igotti@gmail.com>
> > Cc: Paolo Bonzini <pbonzini@redhat.com>
> > Cc: Igor Mammedov <imammedo@redhat.com>
> > Cc: Eduardo Habkost <ehabkost@redhat.com>
> > ---
> > cpus-common.c | 9 ++++-----
> > 1 file changed, 4 insertions(+), 5 deletions(-)
> >
> > diff --git a/cpus-common.c b/cpus-common.c
> > index 55d5df89237..5a7d2f6132b 100644
> > --- a/cpus-common.c
> > +++ b/cpus-common.c
> > @@ -61,13 +61,14 @@ static bool cpu_index_auto_assigned;
> > static int cpu_get_free_index(void)
> > {
> > CPUState *some_cpu;
> > - int cpu_index = 0;
> > + int max_cpu_index = 0;
> >
> > cpu_index_auto_assigned = true;
> > CPU_FOREACH(some_cpu) {
> > - cpu_index++;
> > + max_cpu_index = MAX(some_cpu->cpu_index, max_cpu_index);
> > }
> > - return cpu_index;
> > + max_cpu_index++;
> > + return max_cpu_index;
> > }
>
> OK some ending up with cpu_index = 1 threw off devices that would do
> qemu_get_cpu(0) so I've tweaked the algorithm to:
>
> static int cpu_get_free_index(void)
> {
> CPUState *some_cpu;
> int max_cpu_index = 0;
>
> cpu_index_auto_assigned = true;
> CPU_FOREACH(some_cpu) {
> if (some_cpu->cpu_index >= max_cpu_index) {
> max_cpu_index = some_cpu->cpu_index + 1;
> }
> }
> return max_cpu_index;
> }
>
> >
> > void cpu_list_add(CPUState *cpu)
> > @@ -90,8 +91,6 @@ void cpu_list_remove(CPUState *cpu)
> > return;
> > }
> >
> > - assert(!(cpu_index_auto_assigned && cpu != QTAILQ_LAST(&cpus)));
> > -
> > QTAILQ_REMOVE_RCU(&cpus, cpu, node);
> > cpu->cpu_index = UNASSIGNED_CPU_INDEX;
> > }
>
>
next prev parent reply other threads:[~2020-05-21 15:54 UTC|newest]
Thread overview: 21+ messages / expand[flat|nested] mbox.gz Atom feed top
2020-05-13 17:31 [PATCH v1 0/8] plugins/next (cleanup, cpu_index and lockstep) Alex Bennée
2020-05-13 17:31 ` [PATCH v1 1/8] qemu/plugin: Trivial code movement Alex Bennée
2020-05-13 17:31 ` [PATCH v1 2/8] qemu/plugin: Move !CONFIG_PLUGIN stubs altogether Alex Bennée
2020-05-13 17:31 ` [PATCH v1 3/8] qemu/qemu-plugin: Make qemu_plugin_hwaddr_is_io() hwaddr argument const Alex Bennée
2020-05-13 17:31 ` [PATCH v1 4/8] MAINTAINERS: update the orphaned cpus-common.c file Alex Bennée
2020-05-13 19:26 ` Philippe Mathieu-Daudé
2020-05-13 17:31 ` [PATCH v1 5/8] cpus-common: ensure auto-assigned cpu_indexes don't clash Alex Bennée
2020-05-14 16:27 ` Alex Bennée
2020-05-21 15:53 ` Igor Mammedov [this message]
2020-05-21 17:10 ` Alex Bennée
2020-05-22 8:46 ` Igor Mammedow
2020-05-13 17:31 ` [PATCH v1 6/8] linux-user: properly "unrealize" vCPU object Alex Bennée
2020-05-22 9:35 ` Philippe Mathieu-Daudé
2020-05-13 17:31 ` [PATCH v1 7/8] tests/tcg: add new threadcount test Alex Bennée
2020-05-15 19:51 ` Nikolay Igotti
2020-05-22 9:33 ` Philippe Mathieu-Daudé
2020-05-13 17:32 ` [PATCH v1 8/8] plugins: new lockstep plugin for debugging TCG changes Alex Bennée
2020-05-13 19:25 ` [PATCH v1 0/8] plugins/next (cleanup, cpu_index and lockstep) Philippe Mathieu-Daudé
2020-05-14 0:56 ` no-reply
2020-05-14 1:36 ` no-reply
2020-05-14 1:36 ` no-reply
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