| Message ID | beee275f48a98e42f073ee63221e9610fc9470b5.1606699505.git.asml.silence@gmail.com (mailing list archive) |
|---|---|
| State | New, archived |
| Headers | show |
| Series | cleanups/fix for blk_mq_get_tag() | expand |
On Mon, Nov 30, 2020 at 01:36:25AM +0000, Pavel Begunkov wrote: > blk_mq_get_tag() selects tag_offset in the beginning and doesn't update > it even though the tag set it may have changed hw queue during waiting. > > Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> > --- > block/blk-mq-tag.c | 7 +++++-- > 1 file changed, 5 insertions(+), 2 deletions(-) > > diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c > index 9c92053e704d..dbbf11edf9a6 100644 > --- a/block/blk-mq-tag.c > +++ b/block/blk-mq-tag.c > @@ -101,10 +101,8 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) > return BLK_MQ_NO_TAG; > } > bt = tags->breserved_tags; > - tag_offset = 0; > } else { > bt = tags->bitmap_tags; > - tag_offset = tags->nr_reserved_tags; > } > > tag = __blk_mq_get_tag(data, bt); > @@ -167,6 +165,11 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) > sbitmap_finish_wait(bt, ws, &wait); > > found_tag: > + if (data->flags & BLK_MQ_REQ_RESERVED) > + tag_offset = 0; > + else > + tag_offset = tags->nr_reserved_tags; > + So far, the tag offset is tag-set wide, and 'tag_offset' is same for all tags, looks no need to add the extra check. thanks, Ming
On 03/12/2020 06:49, Ming Lei wrote: > On Mon, Nov 30, 2020 at 01:36:25AM +0000, Pavel Begunkov wrote: >> blk_mq_get_tag() selects tag_offset in the beginning and doesn't update >> it even though the tag set it may have changed hw queue during waiting. >> >> Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> >> --- >> block/blk-mq-tag.c | 7 +++++-- >> 1 file changed, 5 insertions(+), 2 deletions(-) >> >> diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c >> index 9c92053e704d..dbbf11edf9a6 100644 >> --- a/block/blk-mq-tag.c >> +++ b/block/blk-mq-tag.c >> @@ -101,10 +101,8 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) >> return BLK_MQ_NO_TAG; >> } >> bt = tags->breserved_tags; >> - tag_offset = 0; >> } else { >> bt = tags->bitmap_tags; >> - tag_offset = tags->nr_reserved_tags; >> } >> >> tag = __blk_mq_get_tag(data, bt); >> @@ -167,6 +165,11 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) >> sbitmap_finish_wait(bt, ws, &wait); >> >> found_tag: >> + if (data->flags & BLK_MQ_REQ_RESERVED) >> + tag_offset = 0; >> + else >> + tag_offset = tags->nr_reserved_tags; >> + > > So far, the tag offset is tag-set wide, and 'tag_offset' is same for all tags, > looks no need to add the extra check. Thanks for clearing that. I still think that's a good thing to do as more apparent to me and shouldn't be slower -- it unconditionally stores offset on-stack, even for no-wait path (gcc 9.2). With it's optimised more like if (!(data->flags & BLK_MQ_REQ_RESERVED)) tag += tags->nr_reserved_tags; I like assembly a bit more, but not like that matters much.
diff --git a/block/blk-mq-tag.c b/block/blk-mq-tag.c index 9c92053e704d..dbbf11edf9a6 100644 --- a/block/blk-mq-tag.c +++ b/block/blk-mq-tag.c @@ -101,10 +101,8 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) return BLK_MQ_NO_TAG; } bt = tags->breserved_tags; - tag_offset = 0; } else { bt = tags->bitmap_tags; - tag_offset = tags->nr_reserved_tags; } tag = __blk_mq_get_tag(data, bt); @@ -167,6 +165,11 @@ unsigned int blk_mq_get_tag(struct blk_mq_alloc_data *data) sbitmap_finish_wait(bt, ws, &wait); found_tag: + if (data->flags & BLK_MQ_REQ_RESERVED) + tag_offset = 0; + else + tag_offset = tags->nr_reserved_tags; + /* * Give up this allocation if the hctx is inactive. The caller will * retry on an active hctx.
blk_mq_get_tag() selects tag_offset in the beginning and doesn't update it even though the tag set it may have changed hw queue during waiting. Signed-off-by: Pavel Begunkov <asml.silence@gmail.com> --- block/blk-mq-tag.c | 7 +++++-- 1 file changed, 5 insertions(+), 2 deletions(-)