From mboxrd@z Thu Jan 1 00:00:00 1970 Received: from eggs.gnu.org ([2001:4830:134:3::10]:41844) by lists.gnu.org with esmtp (Exim 4.71) (envelope-from ) id 1e1wQ6-00039v-FD for qemu-devel@nongnu.org; Tue, 10 Oct 2017 11:26:12 -0400 Received: from Debian-exim by eggs.gnu.org with spam-scanned (Exim 4.71) (envelope-from ) id 1e1wQ2-0002ez-F6 for qemu-devel@nongnu.org; Tue, 10 Oct 2017 11:26:10 -0400 Received: from mx1.redhat.com ([209.132.183.28]:34470) by eggs.gnu.org with esmtps (TLS1.0:DHE_RSA_AES_256_CBC_SHA1:32) (Exim 4.71) (envelope-from ) id 1e1wQ2-0002ei-4v for qemu-devel@nongnu.org; Tue, 10 Oct 2017 11:26:06 -0400 Date: Tue, 10 Oct 2017 12:25:59 -0300 From: Eduardo Habkost Message-ID: <20171010152559.GB3246@localhost.localdomain> References: <20171004122851.GJ4760@localhost.localdomain> <20171004150816.41ffc161@nial.brq.redhat.com> <20171004163434.GN4760@localhost.localdomain> <20171005110427.647fed06@nial.brq.redhat.com> <20171005170906.GF4015@localhost.localdomain> <20171006102312.3a9a76c2@nial.brq.redhat.com> <20171006114549.GN4015@localhost.localdomain> <20171009091229.661d8c30@nial.brq.redhat.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20171009091229.661d8c30@nial.brq.redhat.com> Subject: Re: [Qemu-devel] [PATCH v1 3/5] xlnx-zcu102: Specify the valid CPUs List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , To: Igor Mammedov Cc: Alistair Francis , Marcel Apfelbaum , Philippe =?iso-8859-1?Q?Mathieu-Daud=E9?= , "qemu-devel@nongnu.org Developers" On Mon, Oct 09, 2017 at 09:12:29AM +0200, Igor Mammedov wrote: > On Fri, 6 Oct 2017 15:06:57 -0700 > Alistair Francis wrote: > > > On Fri, Oct 6, 2017 at 4:45 AM, Eduardo Habkost wrote: > > > On Fri, Oct 06, 2017 at 10:23:12AM +0200, Igor Mammedov wrote: > > >> On Thu, 5 Oct 2017 14:09:06 -0300 > > >> Eduardo Habkost wrote: > > >> > > >> > On Thu, Oct 05, 2017 at 11:04:27AM +0200, Igor Mammedov wrote: > > >> > > On Wed, 4 Oct 2017 14:39:20 -0700 > > >> > > Alistair Francis wrote: > > >> > > > > >> > > > On Wed, Oct 4, 2017 at 9:34 AM, Eduardo Habkost wrote: > > >> > > > > On Wed, Oct 04, 2017 at 03:08:16PM +0200, Igor Mammedov wrote: > > >> > > > >> On Wed, 4 Oct 2017 09:28:51 -0300 > > >> > > > >> Eduardo Habkost wrote: > > >> > > > >> > > >> > > > >> > On Wed, Oct 04, 2017 at 01:12:32PM +0200, Igor Mammedov wrote: > > >> > > > >> > > On Tue, 3 Oct 2017 14:41:17 -0700 > > >> > > > >> > > Alistair Francis wrote: > > >> > > > >> > > > > >> > > > >> > > > On Tue, Oct 3, 2017 at 1:36 PM, Eduardo Habkost wrote: > > >> > > > >> > > > > On Tue, Oct 03, 2017 at 01:05:13PM -0700, Alistair Francis wrote: > > >> > > > >> > > > >> List all possible valid CPU options. > > >> > > > >> > > > >> > > >> > > > >> > > > >> Signed-off-by: Alistair Francis > > >> > > > >> > > > >> --- > > >> > > > >> > > > >> > > >> > > > >> > > > >> hw/arm/xlnx-zcu102.c | 10 ++++++++++ > > >> > > > >> > > > >> hw/arm/xlnx-zynqmp.c | 16 +++++++++------- > > >> > > > >> > > > >> include/hw/arm/xlnx-zynqmp.h | 1 + > > >> > > > >> > > > >> 3 files changed, 20 insertions(+), 7 deletions(-) > > >> > > > >> > > > >> > > >> > > > >> > > > >> diff --git a/hw/arm/xlnx-zcu102.c b/hw/arm/xlnx-zcu102.c > > >> > > > >> > > > >> index 519a16ed98..039649e522 100644 > > >> > > > >> > > > >> --- a/hw/arm/xlnx-zcu102.c > > >> > > > >> > > > >> +++ b/hw/arm/xlnx-zcu102.c > > >> > > > >> > > > >> @@ -98,6 +98,8 @@ static void xlnx_zynqmp_init(XlnxZCU102 *s, MachineState *machine) > > >> > > > >> > > > >> object_property_add_child(OBJECT(machine), "soc", OBJECT(&s->soc), > > >> > > > >> > > > >> &error_abort); > > >> > > > >> > > > >> > > >> > > > >> > > > >> + object_property_set_str(OBJECT(&s->soc), machine->cpu_type, "cpu-type", > > >> > > > >> > > > >> + &error_fatal); > > >> > > > >> > > > > > > >> > > > >> > > > > Do you have plans to support other CPU types to xlnx_zynqmp in > > >> > > > >> > > > > the future? If not, I wouldn't bother adding the cpu-type > > >> > > > >> > > > > property and the extra boilerplate code if it's always going to > > >> > > > >> > > > > be set to cortex-a53. > > >> > > > >> > > > > > >> > > > >> > > > No, it'll always be A53. > > >> > > > >> > > > > > >> > > > >> > > > I did think of that, but I also wanted to use the new option! I also > > >> > > > >> > > > think there is an advantage in sanely handling users '-cpu' option, > > >> > > > >> > > > before now we just ignored it, so I think it still does give a > > >> > > > >> > > > benefit. That'll be especially important on the Xilinx tree (sometimes > > >> > > > >> > > > people use our machines with a different CPU to 'benchmark' or test > > >> > > > >> > > > other CPUs with our CoSimulation setup). So I think it does make sense > > >> > > > >> > > > to keep in. > > >> > > > >> > > if cpu isn't user settable, one could just outright die if cpu_type > > >> > > > >> > > is not NULL and say that user's CLI is wrong. > > >> > > > >> > > (i.e. don't give users illusion that they allowed to use '-cpu') > > >> > > > >> > > > >> > > > >> > Isn't it exactly what this patch does, by setting: > > >> > > > >> > mc->default_cpu_type = ARM_CPU_TYPE_NAME("cortex-a53"); > > >> > > > >> > mc->valid_cpu_types = xlnx_zynqmp_valid_cpus; > > >> > > > >> > ? > > >> > > > >> > > > >> > > > >> > Except that "-cpu cortex-a53" won't die, which is a good thing. > > >> > > > >> allowing "-cpu cortex-a53" here, would allow to use feature parsing > > >> > > > >> which weren't allowed or were ignored before if user supplied '-cpu'. > > >> > > > >> so I'd more strict and refuse any -cpu and break CLI that tries to use it > > >> > > > >> if board has non configurable cpu type. It would be easier to relax > > >> > > > >> restriction later if necessary. > > >> > > > >> > > >> > > > >> using validate_cpus here just to have users for the new code, > > >> > > > >> doesn't seem like valid justification and at that it makes board > > >> > > > >> code more complex where it's not necessary and build in cpu type > > >> > > > >> works just fine. > > >> > > > > > > >> > > > > It's up to the board maintainer to decide what's the best option. > > >> > > > > Both features are independent from each other and can be > > >> > > > > implemented by machine core. > > >> > > > > > >> > > > Noooo! > > >> > > > > > >> > > > My hope with this series is that eventually we could hit a state where > > >> > > > every single machine acts the same way with the -cpu option. > > >> > > > > > >> > > > I really don't like what we do now where some boards use it, some > > >> > > > boards error and some boars just ignore the option. I think we should > > >> > > > agree on something and every machine should follow the same flow so > > >> > > > that users know what to expect when they use the -cpu option. > > >> > > > > > >> > > > If this means we allow machines to specify they don't support the > > >> > > > option or only have a single element in the list of supported options > > >> > > > doesn't really matter, but all machines should do the same thing. > > >> > > > > > >> > > > > > > >> > > > > In either case, the valid_cpu_types feature will be still very > > >> > > > > useful for boards like pxa270 and sa1110, which support -cpu but > > >> > > > > only with specific families of CPU types (grep for > > >> > > > > "strncmp(cpu_type"). > > >> > > > > > > >> > > > >> > > >> > > > >> wrt centralized way to refuse -cpu if board doesn't support it, > > >> > > > >> (which is not really related to this series) following could be done: > > >> > > > >> > > >> > > > >> when cpu_model removal is completely done I plan to replace > > >> > > > >> vl.c > > >> > > > >> cpu_parse_cpu_model(machine_class->default_cpu_type, cpu_model) > > >> > > > >> with > > >> > > > >> cpu_parse_cpu_model(DEFAULT_TARGET_CPU_TYPE, cpu_model) > > >> > > > >> > > >> > > > >> so that we could drop temporary guard > > >> > > > >> > > >> > > > >> if (machine_class->default_cpu_type) { > > >> > > > > > > >> > > > > This sounds good to me, even if we don't reject -cpu on any > > >> > > > > board. > > >> > > > > > > >> > > > > > > >> > > > >> > > >> > > > >> with that it would be possible to tell from machine_run_board_init() > > >> > > > >> that board doesn't provide cpu but user provided '-cpu' > > >> > > > >> so we would be able to: > > >> > > > >> if ((machine_class->default_cpu_type == NULL) && > > >> > > > >> (machine->cpu_type != NULL)) > > >> > > > >> error_fatal("machine doesn't support -cpu option"); > > >> > > > > > > >> > > > > I won't complain too much if a board maintainer really wants to > > >> > > > > make the board reject -cpu completely, but it's up to them. > > >> > > > > > >> > > > I disagree. I think a standard way of doing it is better. At least for > > >> > > > each architecture. The ARM -cpu option is very confusing at the moment > > >> > > > and it really doesn't need to be that bad. > > >> > > > > > >> > > > > > > >> > > > > Personally, I'd prefer to have all boards setting > > >> > > > > default_cpu_type even if they support only one CPU model, so > > >> > > > > clients don't need a special case for boards that don't support > > >> > > > > -cpu. > > >> > > > > > >> > > > I agree, I think having one CPU makes more sense. It makes it easier > > >> > > > to add support for more cpus in the future and allows the users to use > > >> > > > the -cpu option without killing QEMU. > > >> > > I'm considering -cpu option as a legacy one that server 2 purposes now > > >> > > > >> > I'm not sure about "legacy", but the list of purposes looks > > >> > accurate: > > >> > > > >> > > 1: pick cpu type for running instance > > >> > > > >> > This one has no replacement yet, so can we really call it legacy? > > >> not really, it's not going anywhere in near future > > >> > > >> > > > >> > > 2: convert optional features/legacy syntax to global properties > > >> > > for related cpu type > > >> > > > >> > This one has a replacement: -global. But there's a difference > > >> > between saying "-cpu features are implemented using -global" and > > >> > "-cpu features are obsoleted by -global". I don't think we can > > >> > say it's obsolete or legacy unless existing management software > > >> > is changed to be using something else. > > >> > > > >> > > > >> > > > > >> > > It plays ok for machines with single type of cpu but doesn't really scale > > >> > > to more and doesn't work well nor needed if we were to specify cpus on CLI > > >> > > with -device (i.e. build machine from config/CLI) > > >> > > > >> > This is a good point. But -cpu is still a useful shortcut for > > >> > boards that have a single CPU type. What are the arguments we > > >> > have to get rid of it completely? > > >> boards that have single cpu type don't need -cpu. since cpu is not > > >> configurable there. > > > > > > They don't need -cpu, but there's no need to reject "-cpu FOO" if > > > we know FOO is the CPU model used by the board. This is the only > > > difference between what you propose and what Alistair proposes, > > > right? > > > > > > > > >> > > >> > > >> > > So I would not extend usage '-cpu' to boards that have fixed cpu type, > > >> > > because it really useless in that case and confuses users with idea that > > >> > > they have ability/need to specify -cpu on fixed cpu board. > > >> > > > >> > If they try to choose any other CPU model, they will see an error > > >> > message explicitly saying only one CPU type is supported. What > > >> > would be the harm? > > >> I guess I've already pointed drawbacks from interface point of view, > > >> from maintainer pov it will be extra code to maintain valid cpus > > >> vs just 'create_cpu(MY_CPU_TYPE)' > > >> this patch is vivid example of the case > > > > > > With this part I agree. We don't need to add boilerplate code to > > > board init if the CPU model will always be the same. > > > > > > But I would still prefer to do this: > > > > > > create_cpu(MY_CPU_TYPE); // at XXX_init() > > > [...] > > > static void xxx_class_init(...) { > > > mc->default_cpu_type = MY_CPU_TYPE; > > > /* Reason: XXX_init() is hardcoded to MY_CPU_TYPE */ > > > mc->valid_cpu_types = { MY_CPU_TYPE, NULL }; > > > } > > > > I like this option. It doesn't add much code and I think makes it very > > clear to users. > > > > Another thing to point out is that I see users specifying options to > > QEMU all the time that QEMU will just ignore. Imagine people see > > somewhere online that others use '-cpu' and suddenly they think they > > have to. Having this throw an error that '-cpu' isn't supported in > > this case (but is in others) will create confusion of when it > > should/shouldn't be use. I think always allowing it and telling users > > the supported CPUs clears this up. > > patch would look better with what Eduardo suggested above. > at least it will minimize amount of not need code, so I'd go for it. I just see one problem: I don't see an easy way for setting: mc->valid_cpu_types = { MY_CPU_TYPE, NULL }; without one additional static variable for holding the array. So my claim about "only 2 lines of code" is not accurate. But we might do this to make the code shorter and simpler on boards like xlnx_zynqmp: 1) Change the default on TYPE_MACHINE to: mc->valid_cpu_types = { TYPE_CPU, NULL }; This will keep the existing behavior for all boards. 2) mc->valid_cpu_types=NULL be interpreted as "no CPU model except the default is accepted" or "-cpu is not accepted" in machine_run_board_init() (I prefer the former, but both options would be correct) 3) Boards like xlnx_zynqmp could then just do this: static void xxx_class_init(...) { mc->default_cpu_type = MY_CPU_TYPE; /* Reason: XXX_init() is hardcoded to MY_CPU_TYPE */ mc->valid_cpu_types = NULL; } -- Eduardo