Re: [PATCH] Revert "bfq: Fix computation of shallow depth"
On 2/2/21 7:36 PM, Lin Feng wrote: > Hi all, > > On 2/2/21 22:20, Jens Axboe wrote: >> On 2/2/21 5:28 AM, Jan Kara wrote: >>> Hello! >>> >>> On Fri 29-01-21 19:18:08, 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% >>> >>> Looking at sbitmap_get_shallow() again more carefully, I agree that I >>> misunderstood how shallow_depth argument gets used and the original code >>> was correct and I broke it. Thanks for spotting this! >>> >>> What I didn't notice is that shallow_depth indeed gets used for each bitmap >>> word separately and not for bitmap as a whole. I'd say this could use some >>> more documentation but that's unrelated to your revert. So feel free to add: >>> >>> Reviewed-by: Jan Kara >> >> I don't have the original patch (neither directly nor in the archive), so >> I had to hand-apply it. In any case, applied for 5.11, thanks. >> > > Take a look at linux-block.git tree, the hand-applied commit for this patch > is broken, the following changing line is left out: > - 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); > > Sorry for making troubles to you, I will resend this patch with tiny commit > log typo fix(sbimap -> sbitmap) and attaching Jan's Reviewed-by, also thanks > his time for reviewing. > > Hope this time lkml server will not block my patch. Thanks for checking - just send me an incremental and I'll fold it in. -- Jens Axboe
Re: [PATCH] Revert "bfq: Fix computation of shallow depth"
Hi all, On 2/2/21 22:20, Jens Axboe wrote: On 2/2/21 5:28 AM, Jan Kara wrote: Hello! On Fri 29-01-21 19:18:08, 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% Looking at sbitmap_get_shallow() again more carefully, I agree that I misunderstood how shallow_depth argument gets used and the original code was correct and I broke it. Thanks for spotting this! What I didn't notice is that shallow_depth indeed gets used for each bitmap word separately and not for bitmap as a whole. I'd say this could use some more documentation but that's unrelated to your revert. So feel free to add: Reviewed-by: Jan Kara I don't have the original patch (neither directly nor in the archive), so I had to hand-apply it. In any case, applied for 5.11, thanks. Take a look at linux-block.git tree, the hand-applied commit for this patch is broken, the following changing line is left out: - 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); Sorry for making troubles to you, I will resend this patch with tiny commit log typo fix(sbimap -> sbitmap) and attaching Jan's Reviewed-by, also thanks his time for reviewing. Hope this time lkml server will not block my patch. Thanks, linfeng
Re: [PATCH] Revert "bfq: Fix computation of shallow depth"
On 2/2/21 5:28 AM, Jan Kara wrote: > Hello! > > On Fri 29-01-21 19:18:08, 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% > > Looking at sbitmap_get_shallow() again more carefully, I agree that I > misunderstood how shallow_depth argument gets used and the original code > was correct and I broke it. Thanks for spotting this! > > What I didn't notice is that shallow_depth indeed gets used for each bitmap > word separately and not for bitmap as a whole. I'd say this could use some > more documentation but that's unrelated to your revert. So feel free to add: > > Reviewed-by: Jan Kara I don't have the original patch (neither directly nor in the archive), so I had to hand-apply it. In any case, applied for 5.11, thanks. -- Jens Axboe
Re: [PATCH] Revert "bfq: Fix computation of shallow depth"
Hello!
On Fri 29-01-21 19:18:08, 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%
Looking at sbitmap_get_shallow() again more carefully, I agree that I
misunderstood how shallow_depth argument gets used and the original code
was correct and I broke it. Thanks for spotting this!
What I didn't notice is that shallow_depth indeed gets used for each bitmap
word separately and not for bitmap as a whole. I'd say this could use some
more documentation but that's unrelated to your revert. So feel free to add:
Reviewed-by: Jan Kara
to your patch. Thanks.
Honza
>
> 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
> ---
> 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++)
> --
> 2.25.4
>
--
Jan Kara
SUSE Labs, CR
Re: [PATCH] Revert "bfq: Fix computation of shallow depth"
> Il giorno 1 feb 2021, alle ore 08:32, Lin Feng 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-j...@suse.cz/,
> 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
>> ---
>> 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++)
>
Re: [PATCH] Revert "bfq: Fix computation of shallow depth"
> Il giorno 29 gen 2021, alle ore 12:18, Lin Feng ha scritto:
>
> 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%?
>
Bumping to 100% would be a mistake.
Thanks,
Paolo
> Please correct me if I miss something, thanks.
>
> Signed-off-by: Lin Feng
> ---
> 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++)
> --
> 2.25.4
>
Re: [PATCH] Revert "bfq: Fix computation of shallow depth"
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-j...@suse.cz/,
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.
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
---
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++)
