linux-kernel - [PATCH v2 2/2] PM: hibernate: make compression threads configurable

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Message-ID: <b512fe39fc6c03714fb23bf241f9e8d4b6be4ff2.1757577879.git.luoxueqin@kylinos.cn>
Date: Thu, 11 Sep 2025 16:09:51 +0800
From: Xueqin Luo <luoxueqin@...inos.cn>
To: rafael@...nel.org,
	pavel@...nel.org,
	lenb@...nel.org,
	linux-pm@...r.kernel.org,
	linux-kernel@...r.kernel.org
Cc: Xueqin Luo <luoxueqin@...inos.cn>
Subject: [PATCH v2 2/2] PM: hibernate: make compression threads configurable

The number of compression/decompression threads has a direct impact on
hibernate image generation and resume latency. Using more threads can
reduce overall resume time, but on systems with fewer CPU cores it may
also introduce contention and reduce efficiency.

Performance was evaluated on an 8-core ARM system, averaged over 10 runs:

    cmp_threads   hibernate time (s)   resume time (s)
    --------------------------------------------------
          3             12.14              18.86
          4             12.28              17.48
          5             11.09              16.77
          6             11.08              16.44

With 5–6 threads, resume latency improves by approximately 12% compared
to the default 3-thread configuration, with negligible impact on
hibernate time.

This patch introduces a new kernel parameter, `cmp_threads=`, that allows
users and integrators to tune the number of compression/decompression
threads at boot. This provides a way to balance performance and CPU
utilization across a wide range of hardware without recompiling the
kernel.

Signed-off-by: Xueqin Luo <luoxueqin@...inos.cn>
---
 kernel/power/swap.c | 24 ++++++++++++++++++++----
 1 file changed, 20 insertions(+), 4 deletions(-)

diff --git a/kernel/power/swap.c b/kernel/power/swap.c
index bd149a54c081..bf17363ff331 100644
--- a/kernel/power/swap.c
+++ b/kernel/power/swap.c
@@ -519,8 +519,8 @@ static int swap_writer_finish(struct swap_map_handle *handle,
 				CMP_HEADER, PAGE_SIZE)
 #define CMP_SIZE	(CMP_PAGES * PAGE_SIZE)
 
-/* Maximum number of threads for compression/decompression. */
-#define CMP_THREADS	3
+/* Default number of threads for compression/decompression. */
+static int cmp_threads = 3;
 
 /* Minimum/maximum number of pages for read buffering. */
 #define CMP_MIN_RD_PAGES	1024
@@ -703,7 +703,7 @@ static int save_compressed_image(struct swap_map_handle *handle,
 	 * footprint.
 	 */
 	nr_threads = num_online_cpus() - 1;
-	nr_threads = clamp_val(nr_threads, 1, CMP_THREADS);
+	nr_threads = clamp_val(nr_threads, 1, cmp_threads);
 
 	page = (void *)__get_free_page(GFP_NOIO | __GFP_HIGH);
 	if (!page) {
@@ -1241,7 +1241,7 @@ static int load_compressed_image(struct swap_map_handle *handle,
 	 * footprint.
 	 */
 	nr_threads = num_online_cpus() - 1;
-	nr_threads = clamp_val(nr_threads, 1, CMP_THREADS);
+	nr_threads = clamp_val(nr_threads, 1, cmp_threads);
 
 	page = vmalloc_array(CMP_MAX_RD_PAGES, sizeof(*page));
 	if (!page) {
@@ -1703,3 +1703,19 @@ static int __init swsusp_header_init(void)
 }
 
 core_initcall(swsusp_header_init);
+
+static int __init cmp_threads_setup(char *str)
+{
+	int rc = kstrtouint(str, 0, &cmp_threads);
+
+	if (rc)
+		return rc;
+
+	if (cmp_threads < 1)
+		cmp_threads = 1;
+
+	return 1;
+
+}
+
+__setup("cmp_threads=", cmp_threads_setup);
-- 
2.43.0