Hi Dan, Thank you for the review. Please see my reply inline.
> > 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 <[email protected]> > > --- > > 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. How parent flush request will know when corresponding flush is completed? > > > + 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. yes, will fix this. > > > + 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? Requests should progress after notified by ongoing flush completion event. > > > } > > - 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. but this is coalesced flush request? > > +} > > 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? One lock is for work queue and other for virtio flush completion. Thanks, Pankaj
