From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-1.1 required=3.0 tests=DKIM_SIGNED,DKIM_VALID, DKIM_VALID_AU,HEADER_FROM_DIFFERENT_DOMAINS,MAILING_LIST_MULTI,SPF_PASS, UNPARSEABLE_RELAY autolearn=ham autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id BC5B7C43381 for ; Mon, 25 Mar 2019 18:32:23 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 82AD620879 for ; Mon, 25 Mar 2019 18:32:23 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=oracle.com header.i=@oracle.com header.b="G5g/mI+b" Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1730048AbfCYScW (ORCPT ); Mon, 25 Mar 2019 14:32:22 -0400 Received: from aserp2130.oracle.com ([141.146.126.79]:35354 "EHLO aserp2130.oracle.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1729572AbfCYScV (ORCPT ); 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Mon, 25 Mar 2019 18:31:53 +0000 Received: from aserv0122.oracle.com (aserv0122.oracle.com [141.146.126.236]) by aserv0021.oracle.com (8.14.4/8.14.4) with ESMTP id x2PIVrr0030136 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Mon, 25 Mar 2019 18:31:53 GMT Received: from abhmp0016.oracle.com (abhmp0016.oracle.com [141.146.116.22]) by aserv0122.oracle.com (8.14.4/8.14.4) with ESMTP id x2PIVqKh024393; Mon, 25 Mar 2019 18:31:52 GMT Received: from dhcp-burlington7-2nd-B-east-10-152-55-162.usdhcp.oraclecorp.com (/10.152.32.65) by default (Oracle Beehive Gateway v4.0) with ESMTP ; Mon, 25 Mar 2019 11:31:52 -0700 Subject: Re: [PATCH] x86/xen: Add "xen_timer_slop" command line option To: Ryan Thibodeaux Cc: luca abeni , Dario Faggioli , xen-devel@lists.xenproject.org, linux-kernel@vger.kernel.org, oleksandr_andrushchenko@epam.com, tglx@linutronix.de, jgross@suse.com, ryan.thibodeaux@starlab.io References: <1553279397-130201-1-git-send-email-ryan.thibodeaux@starlab.io> <52bfeae7c256faec444b69efe58d363ad60c3fc5.camel@suse.com> <20190323114151.5cebf31b@sweethome> <20190325130530.56603806@luca64> <69e40698-f7ae-11c3-e4b7-dda4f1fadcf6@oracle.com> <20190325141138.GA44413@centos-dev.localdomain> From: Boris Ostrovsky Openpgp: preference=signencrypt Autocrypt: addr=boris.ostrovsky@oracle.com; prefer-encrypt=mutual; keydata= mQINBFH8CgsBEAC0KiOi9siOvlXatK2xX99e/J3OvApoYWjieVQ9232Eb7GzCWrItCzP8FUV PQg8rMsSd0OzIvvjbEAvaWLlbs8wa3MtVLysHY/DfqRK9Zvr/RgrsYC6ukOB7igy2PGqZd+M MDnSmVzik0sPvB6xPV7QyFsykEgpnHbvdZAUy/vyys8xgT0PVYR5hyvhyf6VIfGuvqIsvJw5 C8+P71CHI+U/IhsKrLrsiYHpAhQkw+Zvyeml6XSi5w4LXDbF+3oholKYCkPwxmGdK8MUIdkM d7iYdKqiP4W6FKQou/lC3jvOceGupEoDV9botSWEIIlKdtm6C4GfL45RD8V4B9iy24JHPlom woVWc0xBZboQguhauQqrBFooHO3roEeM1pxXjLUbDtH4t3SAI3gt4dpSyT3EvzhyNQVVIxj2 FXnIChrYxR6S0ijSqUKO0cAduenhBrpYbz9qFcB/GyxD+ZWY7OgQKHUZMWapx5bHGQ8bUZz2 SfjZwK+GETGhfkvNMf6zXbZkDq4kKB/ywaKvVPodS1Poa44+B9sxbUp1jMfFtlOJ3AYB0WDS Op3d7F2ry20CIf1Ifh0nIxkQPkTX7aX5rI92oZeu5u038dHUu/dO2EcuCjl1eDMGm5PLHDSP 0QUw5xzk1Y8MG1JQ56PtqReO33inBXG63yTIikJmUXFTw6lLJwARAQABtDNCb3JpcyBPc3Ry b3Zza3kgKFdvcmspIDxib3Jpcy5vc3Ryb3Zza3lAb3JhY2xlLmNvbT6JAjgEEwECACIFAlH8 CgsCGwMGCwkIBwMCBhUIAgkKCwQWAgMBAh4BAheAAAoJEIredpCGysGyasEP/j5xApopUf4g 9Fl3UxZuBx+oduuw3JHqgbGZ2siA3EA4bKwtKq8eT7ekpApn4c0HA8TWTDtgZtLSV5IdH+9z JimBDrhLkDI3Zsx2CafL4pMJvpUavhc5mEU8myp4dWCuIylHiWG65agvUeFZYK4P33fGqoaS VGx3tsQIAr7MsQxilMfRiTEoYH0WWthhE0YVQzV6kx4wj4yLGYPPBtFqnrapKKC8yFTpgjaK jImqWhU9CSUAXdNEs/oKVR1XlkDpMCFDl88vKAuJwugnixjbPFTVPyoC7+4Bm/FnL3iwlJVE qIGQRspt09r+datFzPqSbp5Fo/9m4JSvgtPp2X2+gIGgLPWp2ft1NXHHVWP19sPgEsEJXSr9 tskM8ScxEkqAUuDs6+x/ISX8wa5Pvmo65drN+JWA8EqKOHQG6LUsUdJolFM2i4Z0k40BnFU/ kjTARjrXW94LwokVy4x+ZYgImrnKWeKac6fMfMwH2aKpCQLlVxdO4qvJkv92SzZz4538az1T m+3ekJAimou89cXwXHCFb5WqJcyjDfdQF857vTn1z4qu7udYCuuV/4xDEhslUq1+GcNDjAhB nNYPzD+SvhWEsrjuXv+fDONdJtmLUpKs4Jtak3smGGhZsqpcNv8nQzUGDQZjuCSmDqW8vn2o hWwveNeRTkxh+2x1Qb3GT46uuQINBFH8CgsBEADGC/yx5ctcLQlB9hbq7KNqCDyZNoYu1HAB Hal3MuxPfoGKObEktawQPQaSTB5vNlDxKihezLnlT/PKjcXC2R1OjSDinlu5XNGc6mnky03q yymUPyiMtWhBBftezTRxWRslPaFWlg/h/Y1iDuOcklhpr7K1h1jRPCrf1yIoxbIpDbffnuyz kuto4AahRvBU4Js4sU7f/btU+h+e0AcLVzIhTVPIz7PM+Gk2LNzZ3/on4dnEc/qd+ZZFlOQ4 KDN/hPqlwA/YJsKzAPX51L6Vv344pqTm6Z0f9M7YALB/11FO2nBB7zw7HAUYqJeHutCwxm7i BDNt0g9fhviNcJzagqJ1R7aPjtjBoYvKkbwNu5sWDpQ4idnsnck4YT6ctzN4I+6lfkU8zMzC gM2R4qqUXmxFIS4Bee+gnJi0Pc3KcBYBZsDK44FtM//5Cp9DrxRQOh19kNHBlxkmEb8kL/pw XIDcEq8MXzPBbxwHKJ3QRWRe5jPNpf8HCjnZz0XyJV0/4M1JvOua7IZftOttQ6KnM4m6WNIZ 2ydg7dBhDa6iv1oKdL7wdp/rCulVWn8R7+3cRK95SnWiJ0qKDlMbIN8oGMhHdin8cSRYdmHK kTnvSGJNlkis5a+048o0C6jI3LozQYD/W9wq7MvgChgVQw1iEOB4u/3FXDEGulRVko6xCBU4 SQARAQABiQIfBBgBAgAJBQJR/AoLAhsMAAoJEIredpCGysGyfvMQAIywR6jTqix6/fL0Ip8G jpt3uk//QNxGJE3ZkUNLX6N786vnEJvc1beCu6EwqD1ezG9fJKMl7F3SEgpYaiKEcHfoKGdh 30B3Hsq44vOoxR6zxw2B/giADjhmWTP5tWQ9548N4VhIZMYQMQCkdqaueSL+8asp8tBNP+TJ PAIIANYvJaD8xA7sYUXGTzOXDh2THWSvmEWWmzok8er/u6ZKdS1YmZkUy8cfzrll/9hiGCTj u3qcaOM6i/m4hqtvsI1cOORMVwjJF4+IkC5ZBoeRs/xW5zIBdSUoC8L+OCyj5JETWTt40+lu qoqAF/AEGsNZTrwHJYu9rbHH260C0KYCNqmxDdcROUqIzJdzDKOrDmebkEVnxVeLJBIhYZUd t3Iq9hdjpU50TA6sQ3mZxzBdfRgg+vaj2DsJqI5Xla9QGKD+xNT6v14cZuIMZzO7w0DoojM4 ByrabFsOQxGvE0w9Dch2BDSI2Xyk1zjPKxG1VNBQVx3flH37QDWpL2zlJikW29Ws86PHdthh Fm5PY8YtX576DchSP6qJC57/eAAe/9ztZdVAdesQwGb9hZHJc75B+VNm4xrh/PJO6c1THqdQ 19WVJ+7rDx3PhVncGlbAOiiiE3NOFPJ1OQYxPKtpBUukAlOTnkKE6QcA4zckFepUkfmBV1wM Jg6OxFYd01z+a+oL Message-ID: <48d80239-08ca-6bd0-84b0-95d0d0ab689c@oracle.com> Date: Mon, 25 Mar 2019 14:31:36 -0400 User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:60.0) Gecko/20100101 Thunderbird/60.4.0 MIME-Version: 1.0 In-Reply-To: <20190325141138.GA44413@centos-dev.localdomain> Content-Type: text/plain; charset=utf-8 Content-Transfer-Encoding: 7bit Content-Language: en-US X-Proofpoint-Virus-Version: vendor=nai engine=5900 definitions=9206 signatures=668685 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=877 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.0.1-1810050000 definitions=main-1903250132 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 3/25/19 10:11 AM, Ryan Thibodeaux wrote: > On Mon, Mar 25, 2019 at 09:43:20AM -0400, Boris Ostrovsky wrote: >> On 3/25/19 8:05 AM, luca abeni wrote: >>> Hi all, >>> >>> On Sat, 23 Mar 2019 11:41:51 +0100 >>> luca abeni wrote: >>> [...] >>>>>> Is there any data that shows effects of using this new parameter? >>>>>> >>>>> Yes, I've done some research and experiments on this. I did it >>>>> together with a friend, which I'm Cc-ing, as I'm not sure we're >>>>> ready/capable to share the results, yet (Luca?). >>>> I think we can easily share the experimental data (cyclictest output >>>> and plots). >>>> >>>> Moreover, we can share the scripts and tools for running the >>>> experiments (so, everyone can easily reproduce the numbers by simply >>>> typing "make" and waiting for some time :) >>>> >>>> >>>> I'll try to package the results and the scripts/tools this evening, >>>> and I'll send them. >>> Sorry for the delay. I put some quick results here: >>> http://retis.santannapisa.it/luca/XenTimers/ >>> (there also is a link to the scripts to be used for reproducing the >>> results). The latencies have been measured by running cyclictest in the >>> guest (see the scripts for details). >>> >>> The picture shows the latencies measured with an unpatched guest kernel >>> and with a guest kernel having TIMER_SLOP set to 1000 (arbitrary small >>> value :). >>> All the experiments have been performed booting the hypervisor with a >>> small timer_slop (the hypervisor's one) value. So, they show that >>> decreasing the hypervisor's timer_slop is not enough to measure low >>> latencies with cyclictest. >> >> >> I have a couple of questions: >> * Does it make sense to make this a tunable for other clockevent devices >> as well? > I gather that would be on a case-by-case basis for very specific > ones. > > For many timers in the kernel, the minimums are determined by the > actual hardware backing the timer, and the minimum can be > adjusted by the clockevent code. This case is special since it > is entirely a software-based implementation in the kernel, where > the actual timer implementation is in the Xen hypervisor. > >> * This patch adjusts min value. Could max value (ever) need a similar >> adjustment? > I cannot think of such a case where that would be helpful, but I > cannot rule that out or speak as an authority. I am asking mostly because you are introducing new interface and I don't want it to change in the future. I suppose if later we decide to add control for the max value we could just expand your current proposal to xen_timer_slop=[min],[max] and keep it to be back-compatible. For the patch: Reviewed-by: Boris Ostrovsky