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Howlett" Cc: "D, Suneeth" , "Liam R. Howlett" , Andrew Morton , maple-tree@lists.infradead.org, linux-mm@kvack.org, linux-kernel@vger.kernel.org, Suren Baghdasaryan , Sidhartha Kumar , Vlastimil Babka , Alice Ryhl , Kuninori Morimoto , Geert Uytterhoeven , Arnd Bergmann , Christian Kujau , SeongJae Park Subject: Re: [PATCH v3 26/30] maple_tree: Use maple copy node for mas_wr_split() Message-ID: References: <20260130205935.2559335-1-Liam.Howlett@oracle.com> <20260130205935.2559335-27-Liam.Howlett@oracle.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: X-Rspamd-Server: rspam12 X-Rspamd-Queue-Id: 6ED2E100002 X-Stat-Signature: coyytacsqtpknnz7mtmcauyc7otxr1ya X-Rspam-User: X-HE-Tag: 1778342552-594456 X-HE-Meta: U2FsdGVkX19G96JvXUru70LjacXyLDGXayNIoxiowS14WMOACuUM287B7UKiz+sli+3CEYNryQVOElnsHLiwo4MaEVv98Z0aJRkQaz9WvxjluLx8B1O5wLbjmxaKRT9FZP441uHb8Ly0ZtQDTubIUeBOtyj5H4CLn8ceQkWE60RqMqUNXWe9K7dO4oIm5RZrZSTCvfCSpuKp5iDJNKtUXKgHfvIDOJ4kdflco0jOI+6SEx8TYnkpmvZb0/7T+SvQq+FAbvn+00P5iGlkzIRwD6wGDDJAvqkESnM82x5NL+RNyM6xLvaKEYsLEEzBd4n7L+Jy4QdHUqu2DqOVz4Q+zZvpBlVYTscfgf3OYJGwaNMsJbU4sBBQN+GkfEKq9dgjS88ot8aYcBPL4pAgR+DnfvnViediHfF77i5emq72cHTjP5OLTHiuD2tqmDGiJXbbzQf7MnmTkjTMdUbJOFridP4ul0nUZofQQNXJGhZtvljPQsSZsWrYSZ3AhzS5UUu7YOE50ehUIMf4dz99HoqQ6z9jyRgzKPeNkdkPfAc8A7wiqBUaba8ilLwEKhxmsSVbvOl5H4HX/01qVLstlwXuV6uY01iMubmq+JJ4ktE33SwcHL6SQQ70bIgbeey2h0sWIU3JftUsMee3K34Cj/0GO2AAOXnWWqmd7cQ0wNRTcaDO9lufv2Z2+6Ail8+NS0tGYvet1+YGmfv40pHe82LkMBkJAmbCaTHx+1ks68pL7qO/5xLdUXp23YUS/qDwEMaEavLxYe+EZotR0VfjPazvqMDHgAVWkORNIsl7TzJlP8u3E1QHcYucA7QRErvP5suK3Ptgj06+LK1Ylbe8B8dlaTExyO83i37nn0ZBSLWY2kNbqfbH3ryKoK2DkDUT0QiJUsGyg5GJfQZgh3TXSwbhn0aEfcBUqR9LSuHD27SaSBo04hNaMZxKkEPyZSKC35yrGC/KxuFMiRl/b9aLC2h DgI6ds8J P5nDEKJnfsI0nOD2bTZA1doIyGWFzieaNS0TLovbfBSm0BPRWPopBmM7F9t/qGlsSVC3ESWBM8Sg5oZf4b6IbDBQDlWldWEugRZLr00jWeFJSJPIBnng+AuduDVPZLrSwgjS1SH+oYWq7kJofI8xQzgWQdFoqEI8KIjcEgTbdKa2dMJedPwyXyDv8KUJfqkSTtjY1hpM7bLSKQ82phkqP0efcfthYHsys3b3QViADgx3uOihptOYYukVVYTn+BOzguBPIRx0UVuPrqeFpkkR++FtVNVjW8iauHwnH772lg6OJ130= Sender: owner-linux-mm@kvack.org Precedence: bulk X-Loop: owner-majordomo@kvack.org List-ID: List-Subscribe: List-Unsubscribe: On Fri, May 08, 2026 at 11:18:31PM +0200, Liam R. Howlett wrote: > On 26/05/08 02:12PM, D, Suneeth wrote: > > We run will-it-scale micro-benchmark as part of our weekly CI for Kernel > > Performance Regression testing between a stable vs rc kernel. We > > observed will-it-scale-thread-brk1 variant was regressing with > > ~9% on an AMD's Turin machine between the kernels v7.0 and > > v7.1-rc1. Bisecting further landed me onto this commit > > 280b792cac62ddadca2935766ca870b438c86323 (maple_tree: Use maple copy node > > for mas_wr_split()) as the first bad > > commit. > > Thank you for this report. > > Considering this is brk1() in thread mode, I'm going to tell you that > this test is seriously flawed and will not produce anything that looks > reasonable. The way it is written will race all over the place and thus > is unreliable. I think Liam's being too nice here. You should understand *what the test is measuring*. That's literally your job as a performance engineer. Go off and read the brk manpage. Then think about a threaded program. And under what circumstances two threads would call brk() at the same time. And what might happen if they do. "line goes up" or "line goes down" isn't necessarily uninteresting, but it's much more useful if it's set in some kind of context.