Am Fr., 29. Jan. 2021 um 16:30 Uhr schrieb Coly Li <colyli@xxxxxxx>:
>
> On 1/29/21 7:28 AM, Kai Krakow wrote:
> > This reverts commit 56b30770b27d54d68ad51eccc6d888282b568cee.
> >
> > With the btree using the `system_wq`, I seem to see a lot more desktop
> > latency than I should.
> >
> > After some more investigation, it looks like the original assumption
> > of 56b3077 no longer is true, and bcache has a very high potential of
> > congesting the `system_wq`. In turn, this introduces laggy desktop
> > performance, IO stalls (at least with btrfs), and input events may be
> > delayed.
> >
> > So let's revert this. It's important to note that the semantics of
> > using `system_wq` previously mean that `btree_io_wq` should be created
> > before and destroyed after other bcache wqs to keep the same
> > assumptions.
> >
> > Cc: Coly Li <colyli@xxxxxxx>
> > Signed-off-by: Kai Krakow <kai@xxxxxxxxxxx>
>
> The patch is OK to me in general. I just feel it might be unnecessary to
> use ordered work queue. The out-of-order system_wq is used for many
> years and works well with bcache journal.
This is why in v3 and later, I migrated this to an unordered queue. I
just wanted to keep the revert as-is, and then the follow-up patch
will fix this. Is that okay or should I squash both commits?
Thanks,
Kai
> > ---
> > drivers/md/bcache/bcache.h | 2 ++
> > drivers/md/bcache/btree.c | 21 +++++++++++++++++++--
> > drivers/md/bcache/super.c | 4 ++++
> > 3 files changed, 25 insertions(+), 2 deletions(-)
> >
> > diff --git a/drivers/md/bcache/bcache.h b/drivers/md/bcache/bcache.h
> > index 1d57f48307e66..b1ed16c7a5341 100644
> > --- a/drivers/md/bcache/bcache.h
> > +++ b/drivers/md/bcache/bcache.h
> > @@ -1042,5 +1042,7 @@ void bch_debug_exit(void);
> > void bch_debug_init(void);
> > void bch_request_exit(void);
> > int bch_request_init(void);
> > +void bch_btree_exit(void);
> > +int bch_btree_init(void);
> >
> > #endif /* _BCACHE_H */
> > diff --git a/drivers/md/bcache/btree.c b/drivers/md/bcache/btree.c
> > index 910df242c83df..952f022db5a5f 100644
> > --- a/drivers/md/bcache/btree.c
> > +++ b/drivers/md/bcache/btree.c
> > @@ -99,6 +99,8 @@
> > #define PTR_HASH(c, k) \
> > (((k)->ptr[0] >> c->bucket_bits) | PTR_GEN(k, 0))
> >
> > +static struct workqueue_struct *btree_io_wq;
> > +
> > #define insert_lock(s, b) ((b)->level <= (s)->lock)
> >
> >
> > @@ -308,7 +310,7 @@ static void __btree_node_write_done(struct closure *cl)
> > btree_complete_write(b, w);
> >
> > if (btree_node_dirty(b))
> > - schedule_delayed_work(&b->work, 30 * HZ);
> > + queue_delayed_work(btree_io_wq, &b->work, 30 * HZ);
> >
> > closure_return_with_destructor(cl, btree_node_write_unlock);
> > }
> > @@ -481,7 +483,7 @@ static void bch_btree_leaf_dirty(struct btree *b, atomic_t *journal_ref)
> > BUG_ON(!i->keys);
> >
> > if (!btree_node_dirty(b))
> > - schedule_delayed_work(&b->work, 30 * HZ);
> > + queue_delayed_work(btree_io_wq, &b->work, 30 * HZ);
> >
> > set_btree_node_dirty(b);
> >
> > @@ -2764,3 +2766,18 @@ void bch_keybuf_init(struct keybuf *buf)
> > spin_lock_init(&buf->lock);
> > array_allocator_init(&buf->freelist);
> > }
> > +
> > +void bch_btree_exit(void)
> > +{
> > + if (btree_io_wq)
> > + destroy_workqueue(btree_io_wq);
> > +}
> > +
> > +int __init bch_btree_init(void)
> > +{
> > + btree_io_wq = create_singlethread_workqueue("bch_btree_io");
> > + if (!btree_io_wq)
> > + return -ENOMEM;
> > +
> > + return 0;
> > +}
> > diff --git a/drivers/md/bcache/super.c b/drivers/md/bcache/super.c
> > index 2047a9cccdb5d..77c5d8b6d4316 100644
> > --- a/drivers/md/bcache/super.c
> > +++ b/drivers/md/bcache/super.c
> > @@ -2821,6 +2821,7 @@ static void bcache_exit(void)
> > destroy_workqueue(bcache_wq);
> > if (bch_journal_wq)
> > destroy_workqueue(bch_journal_wq);
> > + bch_btree_exit();
> >
> > if (bcache_major)
> > unregister_blkdev(bcache_major, "bcache");
> > @@ -2876,6 +2877,9 @@ static int __init bcache_init(void)
> > return bcache_major;
> > }
> >
> > + if (bch_btree_init())
> > + goto err;
> > +
> > bcache_wq = alloc_workqueue("bcache", WQ_MEM_RECLAIM, 0);
> > if (!bcache_wq)
> > goto err;
> >
>
