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From: "Philippe Mathieu-Daudé" <f4bug@amsat.org>
To: "Daniel P. Berrangé" <berrange@redhat.com>,
	"Thomas Huth" <thuth@redhat.com>
Cc: "Peter Maydell" <peter.maydell@linaro.org>,
	"Samuel Thibault" <samuel.thibault@ens-lyon.org>,
	"Andrew Jeffery" <andrew@aj.id.au>,
	"Michael Tokarev" <mjt@tls.msk.ru>,
	"Richard Henderson" <richard.henderson@linaro.org>,
	"qemu-devel@nongnu.org" <qemu-devel@nongnu.org>,
	"Richard W.M. Jones" <rjones@redhat.com>,
	"qemu-arm@nongnu.org" <qemu-arm@nongnu.org>,
	"Joel Stanley" <joel@jms.id.au>, "Peter Delevoryas" <pdel@fb.com>,
	"Paolo Bonzini" <pbonzini@redhat.com>,
	"Stefan Weil" <sw@weilnetz.de>, "Cédric Le Goater" <clg@kaod.org>
Subject: Re: Deprecate 32-bit hosts? (was: Re: [PULL 14/14] hw/arm/aspeed: Add Fuji machine type)
Date: Wed, 15 Sep 2021 10:51:56 +0200	[thread overview]
Message-ID: <a7a8ee29-cfc5-fec4-30fc-761df76107da@amsat.org> (raw)
In-Reply-To: <YUGw1v20jNRxq2zH@redhat.com>

On 9/15/21 10:37 AM, Daniel P. Berrangé wrote:
> On Wed, Sep 15, 2021 at 09:42:48AM +0200, Thomas Huth wrote:
>> On 14/09/2021 17.22, Richard Henderson wrote:
>>> On 9/14/21 5:26 AM, Peter Maydell wrote:
>>>> (2) RAM blocks should have a length that fits inside a
>>>>      signed 32-bit type on 32-bit hosts (at least I assume this
>>>>      is where the 2047MB limit is coming from; in theory this ought
>>>>      to be improveable but auditing the code for mishandling of
>>>>      RAMblock sizes to ensure we weren't accidentally stuffing
>>>>      their size into a signed 'long' somewhere would be kind
>>>>      of painful)
>>>
>>> Recalling that the win64 abi model is p64, i.e. 'long' is still 32-bit
>>> while pointers are 64-bit, how close do we think we are to this being
>>> fixed already?
>>>
>>>> Even if we did fix (2) we'd need to compromise on (3)
>>>> sometimes still -- if a board has 4GB of RAM that's
>>>> not going to fit in 32 bits regardless. But we would be
>>>> able to let boards with 2GB have 2GB.
>>>
>>> I'm not opposed to deprecating 32-bit hosts...  ;-)
>>
>> I think we should consider this again, indeed. Plain 32-bit CPUs are quite
>> seldom these days, aren't they? And I think we urgently need to decrease the
>> amount of things that we have to test and maintain in our CI and developer
>> branches... So is there still a really really compelling reason to keep
>> 32-bit host support alive?
> 
> I think it probably depends on the architecture to some extent.
> 
> i386 is possibly getting rare enough to consider dropping, though
> IIUC, KVM in the kernel still supports it.  Would feel odd to drop
> it in QEMU if the kernel still thinks it is popular enough to keep
> KVM support.
> 
> armv7 feels like it is relatively common as 64-bit didn't arrive
> in widespread use until relatively recent times compared to x86_64.
> KVM dropped armv7, but then hardware for that was never widespread,
> so armv7 was always TCG dominated
> 
> Other 32-bit arches were/are always rare.

While I could understand there are rare uses of system emulation on
32-bit hosts, I still believe user-emulation is used, but would like
to be proven to the contrary. With that in mind, I'm not sure removing
sysemu on 32-bit hosts is worthful. Maybe we should ask distribution
maintainers first, then eventually poll the community? Or start with
a deprecation warning?

>> Could we maybe also decrease the amount of targets, i.e. merge
>> qemu-system-x86_64 and qemu-system-i386, merge qemu-system-ppc64 and
>> qemu-system-ppc, etc. where it makes sense (i.e. where one of the binaries
>> is a superset of the other)?
> 
> Regards,
> Daniel
> 



  reply	other threads:[~2021-09-15  8:52 UTC|newest]

Thread overview: 32+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2021-09-13 16:12 [PULL 00/14] aspeed queue Cédric Le Goater
2021-09-13 16:12 ` [PULL 01/14] hw: arm: aspeed: Enable eth0 interface for aspeed-ast2600-evb Cédric Le Goater
2021-09-13 16:12 ` [PULL 02/14] hw: arm: aspeed: Enable mac0/1 instead of mac1/2 for g220a Cédric Le Goater
2021-09-13 16:12 ` [PULL 03/14] watchdog: aspeed: Sanitize control register values Cédric Le Goater
2021-09-13 16:12 ` [PULL 04/14] watchdog: aspeed: Fix sequential control writes Cédric Le Goater
2021-09-13 16:12 ` [PULL 05/14] hw: aspeed_gpio: Simplify 1.8V defines Cédric Le Goater
2021-09-13 16:12 ` [PULL 06/14] hw: aspeed_gpio: Clarify GPIO controller name Cédric Le Goater
2021-09-13 16:12 ` [PULL 07/14] misc/pca9552: Fix LED status register indexing in pca955x_get_led() Cédric Le Goater
2021-09-13 16:12 ` [PULL 08/14] arm/aspeed: rainier: Add i2c eeproms and muxes Cédric Le Goater
2021-09-13 16:12 ` [PULL 09/14] aspeed: Emulate the AST2600A3 Cédric Le Goater
2021-09-13 16:13 ` [PULL 10/14] hw/misc: Add Infineon DPS310 sensor model Cédric Le Goater
2021-09-13 16:13 ` [PULL 11/14] arm/aspeed: Add DPS310 to Witherspoon and Rainier Cédric Le Goater
2021-09-13 16:13 ` [PULL 12/14] hw/arm/aspeed: Initialize AST2600 UART clock selection registers Cédric Le Goater
2021-09-13 16:13 ` [PULL 13/14] hw/arm/aspeed: Allow machine to set UART default Cédric Le Goater
2021-09-13 16:13 ` [PULL 14/14] hw/arm/aspeed: Add Fuji machine type Cédric Le Goater
2021-09-14 10:56   ` Cédric Le Goater
2021-09-14 11:59     ` Peter Delevoryas
2021-09-14 12:14       ` Joel Stanley
2021-09-14 12:26         ` Peter Maydell
2021-09-14 15:22           ` Richard Henderson
2021-09-15  7:42             ` Deprecate 32-bit hosts? (was: Re: [PULL 14/14] hw/arm/aspeed: Add Fuji machine type) Thomas Huth
2021-09-15  7:54               ` Philippe Mathieu-Daudé
2021-09-15  8:37               ` Daniel P. Berrangé
2021-09-15  8:51                 ` Philippe Mathieu-Daudé [this message]
2021-09-15  9:05                   ` Daniel P. Berrangé
2021-09-16 12:29             ` [PULL 14/14] hw/arm/aspeed: Add Fuji machine type Cédric Le Goater
2021-09-16 13:53               ` Philippe Mathieu-Daudé
2021-09-16 14:06                 ` Cédric Le Goater
2021-09-16 14:07                   ` Peter Maydell
2021-09-14 10:51 ` [PULL 00/14] aspeed queue Peter Maydell
2021-09-14 10:58   ` Cédric Le Goater
2021-09-14 11:38     ` Philippe Mathieu-Daudé

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