linux-kernel - [PATCH v4 7/7] perf threads: Reduce table size from 256 to 8

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Message-Id: <20240301053646.1449657-8-irogers@google.com>
Date: Thu, 29 Feb 2024 21:36:45 -0800
From: Ian Rogers <irogers@...gle.com>
To: Peter Zijlstra <peterz@...radead.org>, Ingo Molnar <mingo@...hat.com>, 
	Arnaldo Carvalho de Melo <acme@...nel.org>, Namhyung Kim <namhyung@...nel.org>, 
	Mark Rutland <mark.rutland@....com>, 
	Alexander Shishkin <alexander.shishkin@...ux.intel.com>, Jiri Olsa <jolsa@...nel.org>, 
	Ian Rogers <irogers@...gle.com>, Adrian Hunter <adrian.hunter@...el.com>, 
	Oliver Upton <oliver.upton@...ux.dev>, Yang Jihong <yangjihong1@...wei.com>, 
	linux-kernel@...r.kernel.org, linux-perf-users@...r.kernel.org
Subject: [PATCH v4 7/7] perf threads: Reduce table size from 256 to 8

The threads data structure is an array of hashmaps, previously
rbtrees. The two levels allows for a fixed outer array where access is
guarded by rw_semaphores. Commit 91e467bc568f ("perf machine: Use
hashtable for machine threads") sized the outer table at 256 entries
to avoid future scalability problems, however, this means the threads
struct is sized at 30,720 bytes. As the hashmaps allow O(1) access for
the common find/insert/remove operations, lower the number of entries
to 8. This reduces the size overhead to 960 bytes.

Signed-off-by: Ian Rogers <irogers@...gle.com>
---
 tools/perf/util/threads.h | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/tools/perf/util/threads.h b/tools/perf/util/threads.h
index d03bd91a7769..da68d2223f18 100644
--- a/tools/perf/util/threads.h
+++ b/tools/perf/util/threads.h
@@ -7,7 +7,7 @@

 struct thread;

-#define THREADS__TABLE_BITS	8
+#define THREADS__TABLE_BITS	3
 #define THREADS__TABLE_SIZE	(1 << THREADS__TABLE_BITS)

 struct threads_table_entry {
-- 
2.44.0.278.ge034bb2e1d-goog