> Il giorno 1 feb 2021, alle ore 08:32, Lin Feng <linf@xxxxxxxxxx> ha scritto: > > Hi, it seems that this patch was blocked by linux mailist servers, so ping again. > > Based on https://patchwork.kernel.org/project/linux-block/patch/20201210094433.25491-1-jack@xxxxxxx/, > it looks like we have made a consensus about bfqd->word_depths[2][2]'s changing, so now the > computation codes for bfq's word_depths array are not necessary and one variable is enough. > > But IMHO async depth limitation for slow drivers is essential, which is what we always did in cfq age. > It is essential. Thanks, Paolo > On 1/29/21 19:18, Lin Feng wrote: >> This reverts commit 6d4d273588378c65915acaf7b2ee74e9dd9c130a. >> bfq.limit_depth passes word_depths[] as shallow_depth down to sbitmap core >> sbitmap_get_shallow, which uses just the number to limit the scan depth of >> each bitmap word, formula: >> scan_percentage_for_each_word = shallow_depth / (1 << sbimap->shift) * 100% >> That means the comments's percentiles 50%, 75%, 18%, 37% of bfq are correct. >> But after commit patch 'bfq: Fix computation of shallow depth', we use >> sbitmap.depth instead, as a example in following case: >> sbitmap.depth = 256, map_nr = 4, shift = 6; sbitmap_word.depth = 64. >> The resulsts of computed bfqd->word_depths[] are {128, 192, 48, 96}, and >> three of the numbers exceed core dirver's 'sbitmap_word.depth=64' limit >> nothing. Do we really don't want limit depth for such workloads, or we >> just want to bump up the percentiles to 100%? >> Please correct me if I miss something, thanks. >> Signed-off-by: Lin Feng <linf@xxxxxxxxxx> >> --- >> block/bfq-iosched.c | 8 ++++---- >> 1 file changed, 4 insertions(+), 4 deletions(-) >> diff --git a/block/bfq-iosched.c b/block/bfq-iosched.c >> index 9e4eb0fc1c16..9e81d1052091 100644 >> --- a/block/bfq-iosched.c >> +++ b/block/bfq-iosched.c >> @@ -6332,13 +6332,13 @@ static unsigned int bfq_update_depths(struct bfq_data *bfqd, >> * limit 'something'. >> */ >> /* no more than 50% of tags for async I/O */ >> - bfqd->word_depths[0][0] = max(bt->sb.depth >> 1, 1U); >> + bfqd->word_depths[0][0] = max((1U << bt->sb.shift) >> 1, 1U); >> /* >> * no more than 75% of tags for sync writes (25% extra tags >> * w.r.t. async I/O, to prevent async I/O from starving sync >> * writes) >> */ >> - bfqd->word_depths[0][1] = max((bt->sb.depth * 3) >> 2, 1U); >> + bfqd->word_depths[0][1] = max(((1U << bt->sb.shift) * 3) >> 2, 1U); >> /* >> * In-word depths in case some bfq_queue is being weight- >> @@ -6348,9 +6348,9 @@ static unsigned int bfq_update_depths(struct bfq_data *bfqd, >> * shortage. >> */ >> /* no more than ~18% of tags for async I/O */ >> - bfqd->word_depths[1][0] = max((bt->sb.depth * 3) >> 4, 1U); >> + bfqd->word_depths[1][0] = max(((1U << bt->sb.shift) * 3) >> 4, 1U); >> /* no more than ~37% of tags for sync writes (~20% extra tags) */ >> - bfqd->word_depths[1][1] = max((bt->sb.depth * 6) >> 4, 1U); >> + bfqd->word_depths[1][1] = max(((1U << bt->sb.shift) * 6) >> 4, 1U); >> for (i = 0; i < 2; i++) >> for (j = 0; j < 2; j++) >
