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Thu, 09 May 2019 02:14:23 +0000 Received: from pps.filterd (aserp3020.oracle.com [127.0.0.1]) by aserp3020.oracle.com (8.16.0.27/8.16.0.27) with SMTP id x492D6oW153932; Thu, 9 May 2019 02:14:22 GMT Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserp3020.oracle.com with ESMTP id 2s9ayfwnsx-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Thu, 09 May 2019 02:14:22 +0000 Received: from abhmp0009.oracle.com (abhmp0009.oracle.com [141.146.116.15]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x492EJJw006773; Thu, 9 May 2019 02:14:19 GMT Received: from Subhras-MacBook-Pro.local (/73.252.215.155) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Wed, 08 May 2019 19:14:19 -0700 Subject: Re: [RFC PATCH v2 11/17] sched: Basic tracking of matching tasks To: Aubrey Li Cc: Tim Chen , Aaron Lu , Vineeth Remanan Pillai , Nishanth Aravamudan , Julien Desfossez , Peter Zijlstra , Ingo Molnar , Thomas Gleixner , Paul Turner , Linus Torvalds , Linux List Kernel Mailing , =?UTF-8?B?RnLDqWTDqXJpYyBXZWlzYmVja2Vy?= , Kees Cook , Greg Kerr , Phil Auld , Aaron Lu , Valentin Schneider , Mel Gorman , Pawan Gupta , Paolo Bonzini References: <2364f2b65bf50826d881c84d7634b6565dfee527.1556025155.git.vpillai@digitalocean.com> <20190429061516.GA9796@aaronlu> <6dfc392f-e24b-e641-2f7d-f336a90415fa@linux.intel.com> <777b7674-4811-dac4-17df-29bd028d6b26@linux.intel.com> <28fb6854-2772-5d29-087a-6a0cf6afe626@oracle.com> <8098b70b-2095-91ea-d4ad-9181829066c7@oracle.com> From: Subhra Mazumdar Message-ID: <7671d3f0-ca07-7260-a855-473ab58d1c30@oracle.com> Date: Wed, 8 May 2019 19:14:17 -0700 User-Agent: Mozilla/5.0 (Macintosh; Intel Mac OS X 10.13; rv:60.0) Gecko/20100101 Thunderbird/60.6.1 MIME-Version: 1.0 In-Reply-To: Content-Type: text/plain; charset=utf-8; format=flowed Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9251 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 suspectscore=0 malwarescore=0 phishscore=0 bulkscore=0 spamscore=0 mlxscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905090011 X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9251 signatures=668686 X-Proofpoint-Spam-Details: rule=notspam policy=default score=0 priorityscore=1501 malwarescore=0 suspectscore=0 phishscore=0 bulkscore=0 spamscore=0 clxscore=1015 lowpriorityscore=0 mlxscore=0 impostorscore=0 mlxlogscore=999 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1905090011 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 5/8/19 6:38 PM, Aubrey Li wrote: > On Thu, May 9, 2019 at 8:29 AM Subhra Mazumdar > wrote: >> >> On 5/8/19 5:01 PM, Aubrey Li wrote: >>> On Thu, May 9, 2019 at 2:41 AM Subhra Mazumdar >>> wrote: >>>> On 5/8/19 11:19 AM, Subhra Mazumdar wrote: >>>>> 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. >>>>> >>>> Ah, my bad. It is per rq. But still can have 2 different cookies. Not sure >>>> why you think it is unlikely? >>> Yeah, I meant 2 different cookies on the system, but unlikely 2 >>> different cookies >>> on one same rq. >>> >>> If I read the source correctly, for the sched_core_balance path, when try to >>> steal cookie from another CPU, sched_core_find() uses dst's cookie to search >>> if there is a cookie match in src's rq, and sched_core_find() returns idle or >>> matched task, and later put this matched task onto dst's rq (activate_task() in >>> sched_core_find()). At this moment, the nodes on the rq's rb tree should have >>> same cookies. >>> >>> Thanks, >>> -Aubrey >> Yes, but sched_core_find is also called from pick_task to find a local >> matching task. > Can a local searching introduce a different cookies? Where is it from? No. I meant the local search uses the same binary search of sched_core_find so it has to be correct. > >> The enqueue side logic of the scheduler is unchanged with >> core scheduling, > But only the task with cookies is placed onto this rb tree? > >> so it is possible tasks with different cookies are >> enqueued on the same rq. So while searching for a matching task locally >> doing it correctly should matter. > May I know how exactly? select_task_rq_* seems to be unchanged. So the search logic to find a cpu to enqueue when a task becomes runnable is same as before and doesn't do any kind of cookie matching. > > Thanks, > -Aubrey