On 01/09/2015 03:25 PM, Mike Snitzer wrote:
> On Fri, Jan 09 2015 at 4:56pm -0500,
> Jens Axboe <axboe@xxxxxxxxx> wrote:
>
>> On 01/09/2015 02:40 PM, Mike Snitzer wrote:
>>> On Fri, Jan 09 2015 at 4:11pm -0500,
>>> Jens Axboe <axboe@xxxxxxxxx> wrote:
>>>
>>>>
>>>> Actually, try this one instead, it should be a bit more precise than
>>>> the first.
>>>>
>>>
>>> Thanks for the test patch.
>>>
>>> I'm still seeing failures that look wrong (last_tag=127 could be edge
>>> condition not handled properly?):
>>>
>>> [ 14.254632] __bt_get: values before for loop: last_tag=127, index=3
>>> [ 14.255841] __bt_get: values after for loop: last_tag=64, index=2
>>> [ 14.257036]
>>> [ 14.257036] bt_get: __bt_get() returned -1
>>> [ 14.258051] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
>>> [ 14.259246] nr_free=128, nr_reserved=0
>>> [ 14.259963] active_queues=0
>>>
>>> [ 213.115997] __bt_get: values before for loop: last_tag=127, index=3
>>> [ 213.117115] __bt_get: values after for loop: last_tag=96, index=3
>>> [ 213.118200]
>>> [ 213.118200] bt_get: __bt_get() returned -1
>>> [ 213.121593] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
>>> [ 213.123960] nr_free=128, nr_reserved=0
>>> [ 213.125880] active_queues=0
>>>
>>> [ 239.158079] __bt_get: values before for loop: last_tag=8, index=0
>>> [ 239.160363] __bt_get: values after for loop: last_tag=0, index=0
>>> [ 239.162896]
>>> [ 239.162896] bt_get: __bt_get() returned -1
>>> [ 239.166284] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
>>> [ 239.168623] nr_free=127, nr_reserved=0
>>> [ 239.170508] active_queues=0
>>
>> Thanks for testing, can you try this one?
>
> Huh, at least now we're now seeing some nr_free=0... but the last 3
> failures below look unnecessary still. E.g. the last_tag=127 case
>
> [ 13.895265] __bt_get: values before for loop: last_tag=59, index=1
> [ 13.895265] __bt_get: values after for loop: last_tag=32, index=1
> [ 13.895266]
> [ 13.895266] bt_get: __bt_get() returned -1
> [ 13.895267] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> [ 13.895267] nr_free=0, nr_reserved=0
> [ 13.895268] active_queues=0
>
> [ 13.895269] __bt_get: values before for loop: last_tag=0, index=0
> [ 13.895270] __bt_get: values after for loop: last_tag=0, index=0
> [ 13.895270]
> [ 13.895270] bt_get: __bt_get() returned -1
> [ 13.895271] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> [ 13.895272] nr_free=0, nr_reserved=0
> [ 13.895272] active_queues=0
> [ 13.895324] __bt_get: values before for loop: last_tag=0, index=0
> [ 13.895324] __bt_get: values after for loop: last_tag=0, index=0
> [ 13.895325] bt_get: __bt_get() _still_ returned -1
> [ 13.895325] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> [ 13.895326] nr_free=0, nr_reserved=0
> [ 13.895326] active_queues=0
>
> [ 18.931425] __bt_get: values before for loop: last_tag=127, index=3
> [ 18.933317] __bt_get: values after for loop: last_tag=0, index=0
> [ 18.935140]
> [ 18.935140] bt_get: __bt_get() returned -1
> [ 18.936807] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> [ 18.938772] nr_free=128, nr_reserved=0
> [ 18.939927] active_queues=0
>
> [ 489.119597] __bt_get: values before for loop: last_tag=95, index=2
> [ 489.120621] __bt_get: values after for loop: last_tag=96, index=3
> [ 489.121624]
> [ 489.121624] bt_get: __bt_get() returned -1
> [ 489.122532] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> [ 489.123581] nr_free=128, nr_reserved=0
> [ 489.124206] active_queues=0
>
> [ 494.705758] __bt_get: values before for loop: last_tag=127, index=3
> [ 494.707797] __bt_get: values after for loop: last_tag=0, index=0
> [ 494.709696]
> [ 494.709696] bt_get: __bt_get() returned -1
> [ 494.712459] queue_num=0, nr_tags=128, reserved_tags=0, bits_per_word=5
> [ 494.714403] nr_free=128, nr_reserved=0
> [ 494.715955] active_queues=0
I sent out the half-done v3, unfortunately. Can you try this? Both the
cases with substantial nr_free are at the end of an index.
If this one doesn't solve it, I'll reproduce it myself to save the
ping-pong effort :-)
--
Jens Axboe
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c
index 60c9d4a93fe4..1ce031a56080 100644
--- a/block/blk-mq-tag.c
+++ b/block/blk-mq-tag.c
@@ -142,29 +142,29 @@ static inline bool hctx_may_queue(struct blk_mq_hw_ctx *hctx,
static int __bt_get_word(struct blk_align_bitmap *bm, unsigned int last_tag)
{
- int tag, org_last_tag, end;
- bool wrap = last_tag != 0;
+ int tag, org_last_tag = last_tag;
- org_last_tag = last_tag;
- end = bm->depth;
- do {
-restart:
- tag = find_next_zero_bit(&bm->word, end, last_tag);
- if (unlikely(tag >= end)) {
+ while (1) {
+ tag = find_next_zero_bit(&bm->word, bm->depth, last_tag);
+ if (unlikely(tag >= bm->depth)) {
/*
* We started with an offset, start from 0 to
* exhaust the map.
*/
- if (wrap) {
- wrap = false;
- end = org_last_tag;
- last_tag = 0;
- goto restart;
+ if (org_last_tag) {
+ last_tag = org_last_tag = 0;
+ continue;
}
return -1;
}
+
+ if (!test_and_set_bit(tag, &bm->word))
+ break;
+
last_tag = tag + 1;
- } while (test_and_set_bit(tag, &bm->word));
+ if (last_tag >= bm->depth - 1)
+ last_tag = 0;
+ }
return tag;
}
@@ -199,9 +199,13 @@ static int __bt_get(struct blk_mq_hw_ctx *hctx, struct blk_mq_bitmap_tags *bt,
goto done;
}
- last_tag = 0;
- if (++index >= bt->map_nr)
+ index++;
+ last_tag = (index << bt->bits_per_word);
+
+ if (index >= bt->map_nr) {
index = 0;
+ last_tag = 0;
+ }
}
*tag_cache = 0;
--
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