Messages in this thread | | | From | Dan Williams <> | Date | Wed, 25 Aug 2021 10:25:40 -0700 | Subject | Re: [RFC v2 1/2] virtio-pmem: Async virtio-pmem flush |
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On Sun, Jul 25, 2021 at 11:09 PM Pankaj Gupta <pankaj.gupta.linux@gmail.com> wrote: > > From: Pankaj Gupta <pankaj.gupta@ionos.com> > > Implement asynchronous flush for virtio pmem using work queue > to solve the preflush ordering issue. Also, coalesce the flush > requests when a flush is already in process. > > Signed-off-by: Pankaj Gupta <pankaj.gupta@ionos.com> > --- > drivers/nvdimm/nd_virtio.c | 72 ++++++++++++++++++++++++++++-------- > drivers/nvdimm/virtio_pmem.c | 10 ++++- > drivers/nvdimm/virtio_pmem.h | 14 +++++++ > 3 files changed, 79 insertions(+), 17 deletions(-) > > diff --git a/drivers/nvdimm/nd_virtio.c b/drivers/nvdimm/nd_virtio.c > index 10351d5b49fa..61b655b583be 100644 > --- a/drivers/nvdimm/nd_virtio.c > +++ b/drivers/nvdimm/nd_virtio.c > @@ -97,29 +97,69 @@ static int virtio_pmem_flush(struct nd_region *nd_region) > return err; > }; > > +static void submit_async_flush(struct work_struct *ws); > + > /* The asynchronous flush callback function */ > int async_pmem_flush(struct nd_region *nd_region, struct bio *bio) > { > - /* > - * Create child bio for asynchronous flush and chain with > - * parent bio. Otherwise directly call nd_region flush. > + /* queue asynchronous flush and coalesce the flush requests */ > + struct virtio_device *vdev = nd_region->provider_data; > + struct virtio_pmem *vpmem = vdev->priv; > + ktime_t req_start = ktime_get_boottime(); > + > + spin_lock_irq(&vpmem->lock); > + /* flush requests wait until ongoing flush completes, > + * hence coalescing all the pending requests. > */ > - if (bio && bio->bi_iter.bi_sector != -1) { > - struct bio *child = bio_alloc(GFP_ATOMIC, 0); > - > - if (!child) > - return -ENOMEM; > - bio_copy_dev(child, bio); > - child->bi_opf = REQ_PREFLUSH; > - child->bi_iter.bi_sector = -1; > - bio_chain(child, bio); > - submit_bio(child); > - return 0; > + wait_event_lock_irq(vpmem->sb_wait, > + !vpmem->flush_bio || > + ktime_before(req_start, vpmem->prev_flush_start), > + vpmem->lock); > + /* new request after previous flush is completed */ > + if (ktime_after(req_start, vpmem->prev_flush_start)) { > + WARN_ON(vpmem->flush_bio); > + vpmem->flush_bio = bio; > + bio = NULL; > + }
Why the dance with ->prev_flush_start vs just calling queue_work() again. queue_work() is naturally coalescing in that if the last work request has not started execution another queue attempt will be dropped.
> + spin_unlock_irq(&vpmem->lock); > + > + if (!bio) { > + INIT_WORK(&vpmem->flush_work, submit_async_flush);
I expect this only needs to be initialized once at driver init time.
> + queue_work(vpmem->pmem_wq, &vpmem->flush_work); > + return 1; > + } > + > + /* flush completed in other context while we waited */ > + if (bio && (bio->bi_opf & REQ_PREFLUSH)) { > + bio->bi_opf &= ~REQ_PREFLUSH; > + submit_bio(bio); > + } else if (bio && (bio->bi_opf & REQ_FUA)) { > + bio->bi_opf &= ~REQ_FUA; > + bio_endio(bio);
It's not clear to me how this happens, shouldn't all flush completions be driven from the work completion?
> } > - if (virtio_pmem_flush(nd_region)) > - return -EIO; > > return 0; > }; > EXPORT_SYMBOL_GPL(async_pmem_flush); > + > +static void submit_async_flush(struct work_struct *ws) > +{ > + struct virtio_pmem *vpmem = container_of(ws, struct virtio_pmem, flush_work); > + struct bio *bio = vpmem->flush_bio; > + > + vpmem->start_flush = ktime_get_boottime(); > + bio->bi_status = errno_to_blk_status(virtio_pmem_flush(vpmem->nd_region)); > + vpmem->prev_flush_start = vpmem->start_flush; > + vpmem->flush_bio = NULL; > + wake_up(&vpmem->sb_wait); > + > + /* Submit parent bio only for PREFLUSH */ > + if (bio && (bio->bi_opf & REQ_PREFLUSH)) { > + bio->bi_opf &= ~REQ_PREFLUSH; > + submit_bio(bio); > + } else if (bio && (bio->bi_opf & REQ_FUA)) { > + bio->bi_opf &= ~REQ_FUA; > + bio_endio(bio); > + }
Shouldn't the wait_event_lock_irq() be here rather than in async_pmem_flush()? That will cause the workqueue to back up and flush requests to coalesce.
> +} > MODULE_LICENSE("GPL"); > diff --git a/drivers/nvdimm/virtio_pmem.c b/drivers/nvdimm/virtio_pmem.c > index 726c7354d465..56780a6140c7 100644 > --- a/drivers/nvdimm/virtio_pmem.c > +++ b/drivers/nvdimm/virtio_pmem.c > @@ -24,6 +24,7 @@ static int init_vq(struct virtio_pmem *vpmem) > return PTR_ERR(vpmem->req_vq); > > spin_lock_init(&vpmem->pmem_lock); > + spin_lock_init(&vpmem->lock);
Why 2 locks?
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