Received-SPF: pass (google.com: domain of linux-kernel-owner@vger.kernel.org designates 2620:137:e000::1:20 as permitted sender) client-ip=2620:137:e000::1:20;
Message-ID: <4e8067e1-0574-c9d2-9d6c-d676d32071bd@linux.vnet.ibm.com>
Date:   Fri, 25 Feb 2022 05:07:15 +0530
MIME-Version: 1.0
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:91.0) Gecko/20100101
 Thunderbird/91.5.0
Subject: Re: [PATCH -V11 2/9] mm/migrate: update node demotion order on
 hotplug events
Content-Language: en-US
To:     Dave Hansen <dave.hansen@intel.com>,
        Dave Hansen <dave.hansen@linux.intel.com>
Cc:     linux-mm@kvack.org, linux-kernel@vger.kernel.org,
        Zi Yan <ziy@nvidia.com>, David Hildenbrand <david@redhat.com>,
        Yang Shi <yang.shi@linux.alibaba.com>,
        Huang Ying <ying.huang@intel.com>,
        Andrew Morton <akpm@linux-foundation.org>
References: <20210721063926.3024591-1-ying.huang@intel.com>
 <20210721063926.3024591-2-ying.huang@intel.com>
 <eb438ddd-2919-73d4-bd9f-b7eecdd9577a@linux.vnet.ibm.com>
 <f5edb9dc-8b25-47c2-9905-09e88e41861b@intel.com>
From:   Abhishek Goel <huntbag@linux.vnet.ibm.com>
In-Reply-To: <f5edb9dc-8b25-47c2-9905-09e88e41861b@intel.com>
Content-Type: text/plain; charset=UTF-8; format=flowed
Content-Transfer-Encoding: 7bit
Precedence: bulk


On 24/02/22 05:35, Dave Hansen wrote:
> On 2/23/22 15:02, Abhishek Goel wrote:
>> If needed, I will provide experiment results and traces that were used
>> to conclude this.
> It would be great if you can provide some more info.  Even just a CPU
> time profile would be helpful.

Average total time taken for SMT=8 to SMT=1 in v5.14 : 20s

Average total time taken for SMT=8 to SMT=1 in v5.15 : 36s

(Observed in system with 150+ CPUs )

>
> It would also be great to understand more about what "hotplug on power
> systems" actually means.  Is this a synthetic benchmark, or are actual
> end-users running into this issue?  Are entire nodes of CPUs going
> offline?  Or is this just doing an offline/online of CPU 22 in a 100-CPU
> NUMA node?
No, this is not a synthetic benchmark. This can be recreated with
entire nodes of CPUs going offline. And the online/offline operations
have been performed by simple scripts. The time observed can also be
verified (for individual CPU or the entire system) by observing CPU-
Hotplug trace which provide consistent result as observed by using
the scripts.