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Fri, 20 Oct 2023 14:42:23 +0200 Message-ID: <7a818250a8f36476f13b57a172fdb1ab23645edc.camel@gmx.de> Subject: Re: Runtime overhead of PREEMPT_DYNAMIC From: Mike Galbraith To: ema@debian.org, linux-kernel@vger.kernel.org Cc: Michal Hocko Date: Fri, 20 Oct 2023 14:42:22 +0200 In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" User-Agent: Evolution 3.42.4 MIME-Version: 1.0 Content-Transfer-Encoding: quoted-printable X-Provags-ID: V03:K1:/VhL3IM3X6vILeJgMbTo4WuranOOMyeE+JMYCLDfTfiaQV4o/bb 9EzRon3OJtlMHsw4cufWCjgqA+21x6OcDHhKpuqvWxh/hjCPm44nR6O/OaNMuYEx27DQr2h OHI/zRowKGGV53B05HMLRn2CpURLUMibfHSN7bIipHMobO4NgqYPcQ9LTZVyc8NdoM3ys1Q 5FeaZXmfHdSyWgJAMw1ig== UI-OutboundReport: notjunk:1;M01:P0:ExrZ2xdOZRY=;v2Tzo4pSN9LaEr/iW73HEqS4SO0 +Sk0I2EqbYGUe0K0khtn2kaxpckw3eTNv0Kg8gUxicrcouX+6tVsr3j3VjunepjuT9Bzg2jOm UULgMb0U2xmD/4ocro8VeGf3EfpI0MGUAxhrJ9thojgDiUNu/+Et5Jj2GGsUxFVnWfPhaL1e0 8dN77D3mZlb4nIgtQks+3CZoHJQzXXJXnM82QxEUsB03Id182zKa/yb8evI0HHFZwoQ4JqK7b IuPXaUU0VhYaR7LqRChrwkmkS4WBfNIG8yywKLhaOtJ9Sb7OEEjFo/jEUg9lh2B6fSKLO0UKT CdEsYPHIHXAxI02mm07mtkkQl48TX+ZPwh9SjNiouCs8+6sY4zPDvb7pTnmN1RgYJCm4ULpY0 Dzf5lQY+0ByhGW8KZrZJDB7wbx57sh6iWiNnt5oji72UHQI5pkANEVx03+1+b9qvPoBGRTppQ 2wUkSQ43vzdPbTohJqdYwE7fKTVpbxKZcN8BMmVwCQXHprLx8NAd/EzrkpjOHKsg3eM8HC4uT rfirsiWfrwV81HPAtDacaQLCnrf8AKSbCLETioLPuTp4Z601u7sZ8K0Z1yb20qYDEeAm88IUH ny64RASEyXVN3fJxnrRbm4aQAenWAjrZjXGcY4DxbkTbza5jY9GA7jNMCcnkLyymw+96HjdxO LK04Kn5afw1tsw6Fc/9i0XfsfCb1ehpdRNSQZCjMUs2Hjh3oky5lBQLuBf3ngbWbYOrp02Duv GecEQP2dZcDHpu99rAeFUkZM+9aq/TYx8U6ZT59HT2Jm/5cbOhMm+Glfp2LcdNVkIB1aEViHl BGzC/Mr07zgnp0jvvbjYhPnZIVpSG95+YMT4G3+aowkgrX4yox84E89vRjXxgN2GRHDLeg3cq oBq6BD8Nn6iTKtvgv/eG1rJGpe0Rurou7mID+Z2/gD4/I6h//Gj1ZnLFo6RpuWCh+Ad1Kz4Lc AiKV4bMim9JS+JeZYhKbmcMSIdc= X-Spam-Status: No, score=-2.1 required=5.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,DKIM_VALID_AU,DKIM_VALID_EF,FREEMAIL_FROM, RCVD_IN_DNSWL_BLOCKED,RCVD_IN_MSPIKE_H4,RCVD_IN_MSPIKE_WL, SPF_HELO_NONE,SPF_PASS autolearn=ham autolearn_force=no version=3.4.6 X-Spam-Checker-Version: SpamAssassin 3.4.6 (2021-04-09) on lindbergh.monkeyblade.net Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org X-Greylist: Sender passed SPF test, not delayed by milter-greylist-4.6.4 (snail.vger.email [0.0.0.0]); Fri, 20 Oct 2023 05:42:42 -0700 (PDT) On Fri, 2023-10-20 at 11:14 +0200, Emanuele Rocca wrote: > > Results of the tbench benchmark: > > - PREEMPT_DYNAMIC=3Dn Throughput 3831.82 MB/sec > - PREEMPT_DYNAMIC=3Dy Throughput 3006.54 MB/sec > - 20% performance degradation with PREEMPT_DYNAMIC > > All the tests above were performed using Linux 6.5.6 on a AMD Ryzen 7 37= 00X > 8-Core CPU. > > Could someone please confirm whether the approach above seems sane and p= erhaps > try and reproduce the results? FWIW I can't reproduce anything like those crazy tbench numbers. It's neither free nor crazy expensive here. It's kinda hard to imagine the author's mailbox surviving submission day were it _that_ horrid, surely something is amiss. i7-4790 (quad+smt) avg cmdline 6.5.8-voluntary 3685.08 3679.93 3704.98 3689.99 1.000 6.5.8-dynamic 3571.62 3568.61 3550.55 3563.59 .965 3651.37 3599.87 3615.18 3622.14 .981 preempt=3Dnone 3459.58 3514.09 3539.88 3504.51 .949 preempt=3Dfull voluntary (my usual) CONFIG_PREEMPT_VOLUNTARY_BUILD=3Dy # CONFIG_PREEMPT_NONE is not set CONFIG_PREEMPT_VOLUNTARY=3Dy # CONFIG_PREEMPT is not set # CONFIG_PREEMPT_DYNAMIC is not set dynamic (same config, just flip dynamic switch) CONFIG_PREEMPT_BUILD=3Dy # CONFIG_PREEMPT_NONE is not set CONFIG_PREEMPT_VOLUNTARY=3Dy # CONFIG_PREEMPT is not set CONFIG_PREEMPT_COUNT=3Dy CONFIG_PREEMPTION=3Dy CONFIG_PREEMPT_DYNAMIC=3Dy