From: Matthew Wilcox <willy@infradead.org>
To: "Liam R. Howlett" <liam@infradead.org>
Cc: "D, Suneeth" <Suneeth.D@amd.com>,
"Liam R. Howlett" <Liam.Howlett@oracle.com>,
Andrew Morton <akpm@linux-foundation.org>,
maple-tree@lists.infradead.org, linux-mm@kvack.org,
linux-kernel@vger.kernel.org,
Suren Baghdasaryan <surenb@google.com>,
Sidhartha Kumar <sidhartha.kumar@oracle.com>,
Vlastimil Babka <vbabka@suse.cz>,
Alice Ryhl <aliceryhl@google.com>,
Kuninori Morimoto <kuninori.morimoto.gx@renesas.com>,
Geert Uytterhoeven <geert@linux-m68k.org>,
Arnd Bergmann <arnd@arndb.de>,
Christian Kujau <lists@nerdbynature.de>,
SeongJae Park <sj@kernel.org>
Subject: Re: [PATCH v3 26/30] maple_tree: Use maple copy node for mas_wr_split()
Date: Sat, 9 May 2026 17:02:17 +0100 [thread overview]
Message-ID: <af9aicT-tJqohpyA@casper.infradead.org> (raw)
In-Reply-To: <wnvu7fwch7vbmmngd5s4pcypaoiuzq6atsdh47nhtfo4rccsxi@kbg53gd5en4o>
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.
next prev parent reply other threads:[~2026-05-09 16:02 UTC|newest]
Thread overview: 44+ messages / expand[flat|nested] mbox.gz Atom feed top
2026-01-30 20:59 [PATCH v3 00/30] maple_tree: Replace big node with maple copy Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 01/30] maple_tree: Fix mas_dup_alloc() sparse warning Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 02/30] maple_tree: Move mas_spanning_rebalance loop to function Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 03/30] maple_tree: Extract use of big node from mas_wr_spanning_store() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 04/30] maple_tree: Remove unnecessary assignment of orig_l index Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 05/30] maple_tree: inline mas_spanning_rebalance() into mas_wr_spanning_rebalance() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 06/30] maple_tree: Make ma_wr_states reliable for reuse in spanning store Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 07/30] maple_tree: Remove l_wr_mas from mas_wr_spanning_rebalance Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 08/30] maple_tree: Don't pass through height in mas_wr_spanning_store Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 09/30] maple_tree: Move maple_subtree_state from mas_wr_spanning_store to mas_wr_spanning_rebalance Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 10/30] maple_tree: Correct right ma_wr_state end pivot in mas_wr_spanning_store() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 11/30] maple_tree: Introduce maple_copy node and use it in mas_spanning_rebalance() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 12/30] maple_tree: Testing update for spanning store Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 13/30] maple_tree: Inline mas_spanning_rebalance_loop() into mas_wr_spanning_rebalance() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 14/30] maple_tree: Change initial big node setup in mas_wr_spanning_rebalance() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 15/30] maple_tree: Introduce ma_leaf_max_gap() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 16/30] maple_tree: Add gap support, slot and pivot sizes for maple copy Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 17/30] maple_tree: Start using maple copy node for destination Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 18/30] maple_tree: inline mas_wr_spanning_rebalance() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 19/30] maple_tree: Remove unnecessary return statements Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 20/30] maple_tree: Separate wr_split_store and wr_rebalance store type code path Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 21/30] maple_tree: Add cp_is_new_root() helper Liam R. Howlett
2026-02-01 0:10 ` SeongJae Park
2026-02-02 14:58 ` Liam R. Howlett
2026-02-02 15:56 ` SeongJae Park
2026-02-02 17:01 ` Liam R. Howlett
2026-02-02 17:53 ` SeongJae Park
2026-02-03 17:26 ` Liam R. Howlett
2026-02-04 6:36 ` SeongJae Park
2026-01-30 20:59 ` [PATCH v3 22/30] maple_tree: Use maple copy node for mas_wr_rebalance() operation Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 23/30] maple_tree: Add test for rebalance calculation off-by-one Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 24/30] maple_tree: Add copy_tree_location() helper Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 25/30] maple_tree: Add cp_converged() helper Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 26/30] maple_tree: Use maple copy node for mas_wr_split() Liam R. Howlett
2026-05-08 8:42 ` D, Suneeth
2026-05-08 21:18 ` Liam R. Howlett
2026-05-09 16:02 ` Matthew Wilcox [this message]
2026-01-30 20:59 ` [PATCH v3 27/30] maple_tree: Remove maple big node and subtree structs Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 28/30] maple_tree: Pass maple copy node to mas_wmb_replace() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 29/30] maple_tree: Don't pass end to mas_wr_append() Liam R. Howlett
2026-01-30 20:59 ` [PATCH v3 30/30] maple_tree: Clean up mas_wr_node_store() Liam R. Howlett
2026-01-31 20:27 ` [PATCH v3 00/30] maple_tree: Replace big node with maple copy Andrew Morton
2026-02-02 15:40 ` Liam R. Howlett
2026-02-02 18:31 ` Andrew Morton
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