Re: [RFC PATCH 0/6] Introduce cluster cpu topology support - Philippe Mathieu-Daudé

From: "Philippe Mathieu-Daudé" <philmd@redhat.com>
To: "wangyanan (Y)" <wangyanan55@huawei.com>,
	qemu-devel@nongnu.org, qemu-arm@nongnu.org
Cc: Barry Song <song.bao.hua@hisilicon.com>,
	Peter Maydell <peter.maydell@linaro.org>,
	Andrew Jones <drjones@redhat.com>,
	Eduardo Habkost <ehabkost@redhat.com>,
	"Michael S . Tsirkin" <mst@redhat.com>,
	Richard Henderson <richard.henderson@linaro.org>,
	Shannon Zhao <shannon.zhaosl@gmail.com>,
	Igor Mammedov <imammedo@redhat.com>,
	Paolo Bonzini <pbonzini@redhat.com>,
	yuzenghui@huawei.com, wanghaibin.wang@huawei.com,
	zhukeqian1@huawei.com, Jiajie Li <lijiajie11@huawei.com>
Subject: Re: [RFC PATCH 0/6] Introduce cluster cpu topology support
Date: Tue, 27 Apr 2021 14:08:21 +0200	[thread overview]
Message-ID: <d21d4ec0-9b2a-c881-5e2c-0542b4166704@redhat.com> (raw)
In-Reply-To: <a883cf7e-b820-9d20-6424-e2add3007e9b@huawei.com>

On 4/27/21 1:00 PM, wangyanan (Y) wrote:
> On 2021/4/27 17:57, Philippe Mathieu-Daudé wrote:
>> On 3/31/21 11:53 AM, Yanan Wang wrote:
>>> Hi,
>>> This series introduces the cluster cpu topology support, besides now
>>> existing sockets, cores, and threads.
>>>
>>> A cluster means a group of cores that share some resources (e.g. cache)
>>> among them under the LLC. For example, ARM64 server chip Kunpeng 920 has
>>> 6 or 8 clusters in each NUMA, and each cluster has 4 cores. All clusters
>>> share L3 cache data while cores within each cluster share the L2 cache.
>>>
>>> Also, there are some x86 CPU implementations (e.g. Jacobsville) where L2
>>> cache is shared among a cluster of cores instead of being exclusive to
>>> one single core. For example, on Jacobsville there are 6 clusters of 4
>>> Atom cores, each cluster sharing a separate L2, and 24 cores sharing
>>> L3).
>>> About this series:
>>> Note that, this series was implemented based on [3] and [4]. Although
>>> they
>>> have not merged into qemu mainline for now, it's still meaning to
>>> post this
>>> series to express the thoughts first. So a RFC is sent and any
>>> comments are
>>> welcomed and appreciated.
>> At a glance: tests/unit/test-x86-cpuid.c should be adapted to be generic
>> (but still supporting target-specific sub-tests) and some aarch64 tests
>> added.
>>
>> Similarly the ARM PPTT tables tested in tests/qtest/bios-tables-test.c.
>>
>> Otherwise, the overall series looks good and coherent, but it isn't my
>> area :)
> Thank you for the reminder of the related tests. :)
> I will have some work to make them cover the new features introduced
> by this series.

BTW if after 4 weeks and 2 pings nobody sent negative feedback or
NAcked your series, it usually means the community is not against
your purposal, but has some doubts this feature is necessary or
well designed. Tests help to show your work is safe, as it doesn't
break anything. You might need to better explain why this feature
is needed, and what are the limitations of what is currently
possible.

OTOH QEMU has been in "feature freeze" for the next v6.0 release
for the same amount of time, so maybe the maintainers/reviewers
were busy with bugs and still have your series in their TODO list.

Regards,

Phil.