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Re: [Qemu-devel] [PATCH RFC] Implement GIC-500 from GICv3 family for arm

From: Shannon Zhao
Subject: Re: [Qemu-devel] [PATCH RFC] Implement GIC-500 from GICv3 family for arm64
Date: Tue, 10 Mar 2015 17:50:06 +0800
User-agent: Mozilla/5.0 (Windows NT 6.1; rv:24.0) Gecko/20100101 Thunderbird/24.4.0

On 2015/3/10 17:34, Shlomo Pongratz wrote:
> On 10 آذار, 2015 ص 03:18, Shannon Zhao wrote:
>> On 2015/3/9 22:41, address@hidden wrote:
>>> From: Shlomo Pongratz <address@hidden>
>>> This patch is a first step toward 128 cores support for arm64.
>>> At first only 64 cores are supported for two reasons:
>>> First the largest integer type has the size of 64 bits and modifying
>>> essential data structures in order to support 128 cores will require
>>> the usage of bitops.
>>> Second currently the Linux (kernel) can be configured to support
>>> up to 64 cores thus there is no urgency with 128 cores support.
>>> Things left to do:
>>> Currently the booting Linux may got stuck. The probability of getting stuck
>>> increases with the number of cores. I'll appreciate core review.
>>> There is a need to support flexible clusters size. The GIC-500 can support
>>> up to 128 cores, up to 32 clusters and up to 8 cores is a cluster.
>>> So for example, if one wishes to have 16 cores, the options are:
>>> 2 clusters of 8 cores each, 4 clusters with 4 cores each
>>> Currently only the first option is supported.
>>> There is an issue of passing clock affinity to via the dtb. In the dtb
>>> interrupt section there are only 24 bit left to affinity since the
>>> variable is a 32 bit entity and 8 bits are reserved for flags.
>>> See Documentation/devicetree/bindings/arm/arch_timer.txt.
>>> Note that this issue is not seems to be critical as when checking
>>> /proc/irq/3/smp_affinity with 32 cores all 32 bits are one.
>>> The last issue is to add support for 128 cores. This requires the usage
>>> of bitops and currently can be tested up to 64 cores.
>>> Signed-off-by: Shlomo Pongratz <address@hidden>
>>> ---
>>>   hw/arm/Makefile.objs               |    2 +-
>>>   hw/arm/virtv2.c                    |  774 +++++++++++++++++
>> Hi,
>> I think here you want to introduce GICv3 in this patch. So is this necessary 
>> to
>> add a new virtv2 machine? And the codes of this machine mostly are same with 
>> virt.
>> Maybe we can add a parameter such as -GICv3 for machine virt to choose GICv3 
>> for it
>> and choose GICv2 without this parameter. Then we can reuse more codes.
> Hi Shannon,
> Using a parameter and configuring the virtual machine makes the core
> unreadable.
> There are to many if then...else statements.

Sorry, I don't think so. As we have implement GICv3 in qemu using a parameter 
just about 10 if then...else statements are needed. The repeat codes are huge
compared with those statements.


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