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Subject: Re: [RFC PATCH v2 11/17] sched: Basic tracking of matching tasks
To:     Aubrey Li <aubrey.intel@gmail.com>,
        Tim Chen <tim.c.chen@linux.intel.com>
Cc:     Aaron Lu <aaron.lu@linux.alibaba.com>,
        Vineeth Remanan Pillai <vpillai@digitalocean.com>,
        Nishanth Aravamudan <naravamudan@digitalocean.com>,
        Julien Desfossez <jdesfossez@digitalocean.com>,
        Peter Zijlstra <peterz@infradead.org>,
        Ingo Molnar <mingo@kernel.org>,
        Thomas Gleixner <tglx@linutronix.de>,
        Paul Turner <pjt@google.com>,
        Linus Torvalds <torvalds@linux-foundation.org>,
        Linux List Kernel Mailing <linux-kernel@vger.kernel.org>,
        =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= <fweisbec@gmail.com>,
        Kees Cook <keescook@chromium.org>,
        Greg Kerr <kerrnel@google.com>, Phil Auld <pauld@redhat.com>,
        Aaron Lu <aaron.lwe@gmail.com>,
        Valentin Schneider <valentin.schneider@arm.com>,
        Mel Gorman <mgorman@techsingularity.net>,
        Pawan Gupta <pawan.kumar.gupta@linux.intel.com>,
        Paolo Bonzini <pbonzini@redhat.com>
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 <CAERHkrvU0nay-cG9equdOBejOZ5Ffdxo+67ZRp9q0L9BQkcAtQ@mail.gmail.com>
From:   Subhra Mazumdar <subhra.mazumdar@oracle.com>
Message-ID: <eb9abb34-d946-c63c-750b-8f52ed842670@oracle.com>
Date:   Wed, 8 May 2019 11:19:46 -0700
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On 5/8/19 8:49 AM, Aubrey Li wrote:
>> Pawan ran an experiment setting up 2 VMs, with one VM doing a parallel kernel build and one VM doing sysbench,
>> limiting both VMs to run on 16 cpu threads (8 physical cores), with 8 vcpu for each VM.
>> Making the fix did improve kernel build time by 7%.
> I'm gonna agree with the patch below, but just wonder if the testing
> result is consistent,
> as I didn't see any improvement in my testing environment.
>
> IIUC, from the code behavior, especially for 2 VMs case(only 2
> different cookies), the
> per-rq rb tree unlikely has nodes with different cookies, that is, all
> the nodes on this
> tree should have the same cookie, so:
> - if the parameter cookie is equal to the rb tree cookie, we meet a
> match and go the
> third branch
> - else, no matter we go left or right, we can't find a match, and
> we'll return idle thread
> finally.
>
> Please correct me if I was wrong.
>
> Thanks,
> -Aubrey
This is searching in the per core rb tree (rq->core_tree) which can have
2 different cookies. But having said that, even I didn't see any
improvement with the patch for my DB test case. But logically it is
correct.