Re: [PATCH 1/3] lib/raid6: Divide the raid6 algorithm selection process into two parts

[Li Nan <linan666@huaweicloud.com>]

在 2026/1/28 18:49, sunliming@linux.dev 写道:
> From: sunliming <sunliming@kylinos.cn>
> 
> Divide the RAID6 algorithm selection process into two parts: fast selection
> and benchmark selection. To prepare for the asynchronous processing of
> the benchmark phase.
> 
> Signed-off-by: sunliming <sunliming@kylinos.cn>
> ---
>   lib/raid6/algos.c | 76 +++++++++++++++++++++++++++++++----------------
>   1 file changed, 51 insertions(+), 25 deletions(-)
> 
> diff --git a/lib/raid6/algos.c b/lib/raid6/algos.c
> index 799e0e5eac26..ac6a77b0ae1d 100644
> --- a/lib/raid6/algos.c
> +++ b/lib/raid6/algos.c
> @@ -134,7 +134,7 @@ const struct raid6_recov_calls *const raid6_recov_algos[] = {
>   static inline const struct raid6_recov_calls *raid6_choose_recov(void)
>   {
>   	const struct raid6_recov_calls *const *algo;
> -	const struct raid6_recov_calls *best;
> +	const struct raid6_recov_calls *best = NULL;
>   
>   	for (best = NULL, algo = raid6_recov_algos; *algo; algo++)
>   		if (!best || (*algo)->priority > best->priority)
> @@ -152,24 +152,44 @@ static inline const struct raid6_recov_calls *raid6_choose_recov(void)
>   	return best;
>   }
>   
> -static inline const struct raid6_calls *raid6_choose_gen(
> -	void *(*const dptrs)[RAID6_TEST_DISKS], const int disks)
> +/* Quick selection: selects the first valid algorithm. */
> +static inline const struct raid6_calls *raid6_choose_gen_fast(void)
> +{
> +	const struct raid6_calls *const *algo;
> +	const struct raid6_calls *best = NULL;
> +
> +	for (algo = raid6_algos; *algo; algo++) {
> +		if ((*algo)->valid && !(*algo)->valid())
> +			continue;
This logic is odd. We should select the highest-priority algorithm
instead of the first one. This was introduced by commit be85f93ae2df
("lib/raid6: add option to skip algorithm benchmarking").

After fix, this logic is identical to raid6_choose_recov(). Could we reuse
it after renaming the function?


> +
> +		best = *algo;
> +		break;
> +	}
> +
> +	if (best) {
> +		raid6_call = *best;
> +		pr_info("raid6: skipped pq benchmark and selected %s\n",
> +			best->name);
> +	} else {
> +		pr_err("raid6: No valid algorithm found even for fast selection!\n");
> +	}
> +
> +	return best;
> +}
> +
> +static inline const struct raid6_calls *raid6_gen_benchmark(
> +		void *(*const dptrs)[RAID6_TEST_DISKS], const int disks)
>   {
>   	unsigned long perf, bestgenperf, j0, j1;
>   	int start = (disks>>1)-1, stop = disks-3;	/* work on the second half of the disks */
>   	const struct raid6_calls *const *algo;
> -	const struct raid6_calls *best;
> +	const struct raid6_calls *best = NULL;
>   
>   	for (bestgenperf = 0, best = NULL, algo = raid6_algos; *algo; algo++) {
>   		if (!best || (*algo)->priority >= best->priority) {
>   			if ((*algo)->valid && !(*algo)->valid())
>   				continue;
>   
> -			if (!IS_ENABLED(CONFIG_RAID6_PQ_BENCHMARK)) {
> -				best = *algo;
> -				break;
> -			}
> -
>   			perf = 0;
>   
>   			preempt_disable();
> @@ -200,12 +220,6 @@ static inline const struct raid6_calls *raid6_choose_gen(
>   
>   	raid6_call = *best;
>   
> -	if (!IS_ENABLED(CONFIG_RAID6_PQ_BENCHMARK)) {
> -		pr_info("raid6: skipped pq benchmark and selected %s\n",
> -			best->name);
> -		goto out;
> -	}
> -
>   	pr_info("raid6: using algorithm %s gen() %ld MB/s\n",
>   		best->name,
>   		(bestgenperf * HZ * (disks - 2)) >>
> @@ -235,16 +249,11 @@ static inline const struct raid6_calls *raid6_choose_gen(
>   	return best;
>   }
>   
> -
>   /* Try to pick the best algorithm */
>   /* This code uses the gfmul table as convenient data set to abuse */
> -
> -int __init raid6_select_algo(void)
> +static int raid6_choose_gen_benmark(const struct raid6_calls **gen_best)
>   {
>   	const int disks = RAID6_TEST_DISKS;
> -
> -	const struct raid6_calls *gen_best;
> -	const struct raid6_recov_calls *rec_best;
>   	char *disk_ptr, *p;
>   	void *dptrs[RAID6_TEST_DISKS];
>   	int i, cycle;
> @@ -269,14 +278,31 @@ int __init raid6_select_algo(void)
>   	if ((disks - 2) * PAGE_SIZE % 65536)
>   		memcpy(p, raid6_gfmul, (disks - 2) * PAGE_SIZE % 65536);
>   
> -	/* select raid gen_syndrome function */
> -	gen_best = raid6_choose_gen(&dptrs, disks);
> +	*gen_best = raid6_gen_benchmark(&dptrs, disks);
> +
> +	free_pages((unsigned long)disk_ptr, RAID6_TEST_DISKS_ORDER);
> +
> +	return 0;
> +}
> +
> +int __init raid6_select_algo(void)
> +{
> +	int ret;
> +	const struct raid6_calls *gen_best = NULL;
> +	const struct raid6_recov_calls *rec_best = NULL;
> +
> +	/* select raid gen_syndrome functions */
> +	if (!IS_ENABLED(CONFIG_RAID6_PQ_BENCHMARK))
> +		gen_best = raid6_choose_gen_fast();
> +	else {
> +		ret = raid6_choose_gen_benmark(&gen_best);

'gen_best' is meaningless, use 'ret' directly. The input parameter of 
raid6_choose_gen_benchmark() can be modified to void.

> +		if (ret < 0)
> +			return ret;
> +	}
>   
>   	/* select raid recover functions */
>   	rec_best = raid6_choose_recov();
>   
> -	free_pages((unsigned long)disk_ptr, RAID6_TEST_DISKS_ORDER);
> -
>   	return gen_best && rec_best ? 0 : -EINVAL;
>   }
>   

-- 
Thanks,
Nan