Re: [PATCH] PM: hibernate: make compression threads configurable via kernel parameter

[luoxueqin <luoxueqin@kylinos.cn>]

在 2025/8/26 19:43, Rafael J. Wysocki 写道:
> On Tue, Aug 26, 2025 at 11:19 AM Xueqin Luo <luoxueqin@kylinos.cn> wrote:
>> A new kernel parameter 'cmp_threads=' is introduced to
>> allow tuning the number of compression/decompression threads at boot.
> And why is it useful/needed?
The number of compression/decompression threads directly impacts 
hibernate and resume time.
In our tests(averaged over 10 runs):
     cmp_threads   hibernate(s)   resume(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 ~12% compared to 3 threads. 
But on low-core systems,
more threads may cause contention. Making it configurable allows 
integrators to balance performance
  and CPU usage across different hardware without recompiling the kernel.
>> Signed-off-by: Xueqin Luo <luoxueqin@kylinos.cn>
>> ---
>>   kernel/power/swap.c | 22 +++++++++++++++++-----
>>   1 file changed, 17 insertions(+), 5 deletions(-)
>>
>> diff --git a/kernel/power/swap.c b/kernel/power/swap.c
>> index ad13c461b657..43280e08a4ad 100644
>> --- a/kernel/power/swap.c
>> +++ b/kernel/power/swap.c
>> @@ -520,7 +520,8 @@ static int swap_writer_finish(struct swap_map_handle *handle,
>>   #define CMP_SIZE       (CMP_PAGES * PAGE_SIZE)
>>
>>   /* Maximum number of threads for compression/decompression. */
>> -#define CMP_THREADS    3
>> +#define CMP_MAX_THREADS        12
>> +static int cmp_threads = 3
>>
>>   /* Minimum/maximum number of pages for read buffering. */
>>   #define CMP_MIN_RD_PAGES       1024
>> @@ -585,8 +586,8 @@ struct crc_data {
>>          wait_queue_head_t go;                     /* start crc update */
>>          wait_queue_head_t done;                   /* crc update done */
>>          u32 *crc32;                               /* points to handle's crc32 */
>> -       size_t *unc_len[CMP_THREADS];             /* uncompressed lengths */
>> -       unsigned char *unc[CMP_THREADS];          /* uncompressed data */
>> +       size_t *unc_len[CMP_MAX_THREADS];             /* uncompressed lengths */
>> +       unsigned char *unc[CMP_MAX_THREADS];          /* uncompressed data */
>>   };
>>
>>   /*
>> @@ -703,7 +704,7 @@ 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) {
>> @@ -1223,7 +1224,7 @@ 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_size(CMP_MAX_RD_PAGES, sizeof(*page)));
>>          if (!page) {
>> @@ -1667,3 +1668,14 @@ 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;
>> +       return 1;
>> +
>> +}
>> +
>> +__setup("cmp_threads=", cmp_threads_setup);
>> --
>> 2.43.0
>>