On November 26, 2019 1:16:51 AM PST, Zhengyuan Liu <liuzhengyuan@xxxxxxxxxx> wrote:
>For raid6, we need at least 4 disks to calculate the best algorithm.
>But, currently we assume we are always under 4k PAGE_SIZE, when come
>to larger page size, such as 64K, we may get a wrong xor() and gen().
>
>This patch tries to fix the problem by supporting arbitrarily page
>size.
>
>Signed-off-by: Zhengyuan Liu <liuzhengyuan@xxxxxxxxxx>
>---
> lib/raid6/algos.c | 25 +++++++++++++++----------
> 1 file changed, 15 insertions(+), 10 deletions(-)
>
>diff --git a/lib/raid6/algos.c b/lib/raid6/algos.c
>index 17417ee..0df7d99 100644
>--- a/lib/raid6/algos.c
>+++ b/lib/raid6/algos.c
>@@ -118,6 +118,7 @@ const struct raid6_recov_calls *const
>raid6_recov_algos[] = {
>
> #ifdef __KERNEL__
> #define RAID6_TIME_JIFFIES_LG2 4
>+#define RAID6_DATA_BLOCK_LEN 4096
> #else
> /* Need more time to be stable in userspace */
> #define RAID6_TIME_JIFFIES_LG2 9
>@@ -146,7 +147,7 @@ static inline const struct raid6_recov_calls
>*raid6_choose_recov(void)
> }
>
> static inline const struct raid6_calls *raid6_choose_gen(
>- void *(*const dptrs)[(65536/PAGE_SIZE)+2], const int disks)
>+ void *(*const dptrs)[(65536/RAID6_DATA_BLOCK_LEN)+2], const int
>disks)
> {
> unsigned long perf, bestgenperf, bestxorperf, j0, j1;
> int start = (disks>>1)-1, stop = disks-3; /* work on the second half
>of the disks */
>@@ -171,7 +172,7 @@ static inline const struct raid6_calls
>*raid6_choose_gen(
> cpu_relax();
> while (time_before(jiffies,
> j1 + (1<<RAID6_TIME_JIFFIES_LG2))) {
>- (*algo)->gen_syndrome(disks, PAGE_SIZE, *dptrs);
>+ (*algo)->gen_syndrome(disks, RAID6_DATA_BLOCK_LEN, *dptrs);
> perf++;
> }
> preempt_enable();
>@@ -181,7 +182,8 @@ static inline const struct raid6_calls
>*raid6_choose_gen(
> best = *algo;
> }
> pr_info("raid6: %-8s gen() %5ld MB/s\n", (*algo)->name,
>- (perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
>+ (perf*HZ*RAID6_DATA_BLOCK_LEN*(disks-2)) >> \
>+ (20+RAID6_TIME_JIFFIES_LG2));
>
> if (!(*algo)->xor_syndrome)
> continue;
>@@ -195,7 +197,7 @@ static inline const struct raid6_calls
>*raid6_choose_gen(
> while (time_before(jiffies,
> j1 + (1<<RAID6_TIME_JIFFIES_LG2))) {
> (*algo)->xor_syndrome(disks, start, stop,
>- PAGE_SIZE, *dptrs);
>+ RAID6_DATA_BLOCK_LEN, *dptrs);
> perf++;
> }
> preempt_enable();
>@@ -204,17 +206,20 @@ static inline const struct raid6_calls
>*raid6_choose_gen(
> bestxorperf = perf;
>
> pr_info("raid6: %-8s xor() %5ld MB/s\n", (*algo)->name,
>- (perf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2+1));
>+ (perf*HZ*RAID6_DATA_BLOCK_LEN*(disks-2)) >> \
>+ (20+RAID6_TIME_JIFFIES_LG2+1));
> }
> }
>
> if (best) {
> pr_info("raid6: using algorithm %s gen() %ld MB/s\n",
> best->name,
>- (bestgenperf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2));
>+ (bestgenperf*HZ*RAID6_DATA_BLOCK_LEN*(disks-2)) >> \
>+ (20+RAID6_TIME_JIFFIES_LG2));
> if (best->xor_syndrome)
> pr_info("raid6: .... xor() %ld MB/s, rmw enabled\n",
>- (bestxorperf*HZ) >> (20-16+RAID6_TIME_JIFFIES_LG2+1));
>+ (bestxorperf*HZ*RAID6_DATA_BLOCK_LEN*(disks-2)) \
>+ >> (20+RAID6_TIME_JIFFIES_LG2+1));
> raid6_call = *best;
> } else
> pr_err("raid6: Yikes! No algorithm found!\n");
>@@ -228,16 +233,16 @@ static inline const struct raid6_calls
>*raid6_choose_gen(
>
> int __init raid6_select_algo(void)
> {
>- const int disks = (65536/PAGE_SIZE)+2;
>+ const int disks = (65536/RAID6_DATA_BLOCK_LEN)+2;
>
> const struct raid6_calls *gen_best;
> const struct raid6_recov_calls *rec_best;
> char *syndromes;
>- void *dptrs[(65536/PAGE_SIZE)+2];
>+ void *dptrs[(65536/RAID6_DATA_BLOCK_LEN)+2];
> int i;
>
> for (i = 0; i < disks-2; i++)
>- dptrs[i] = ((char *)raid6_gfmul) + PAGE_SIZE*i;
>+ dptrs[i] = ((char *)raid6_gfmul) + RAID6_DATA_BLOCK_LEN*i;
>
> /* Normal code - use a 2-page allocation to avoid D$ conflict */
> syndromes = (void *) __get_free_pages(GFP_KERNEL, 1);
32K, not 4K; it assumes 64K is enough for at least two "disks".
However, as you point out here, there really isn't any particular reason to not just use a 4K chunk for the benchmark; no need to spend a bunch of extra time.
--
Sent from my Android device with K-9 Mail. Please excuse my brevity.
