drbd: improve usage of MSG_MORE

It seems to improve performance if we allow the "p_data" header in its
own frame (no MSG_MORE), but sendpage all but the last page with MSG_MORE.
This is also in preparation of a later zero copy receive implementation.

Suggested by Eduard.Guzovsky@stratus.com on drbd-dev.

Signed-off-by: Philipp Reisner <philipp.reisner@linbit.com>
Signed-off-by: Lars Ellenberg <lars.ellenberg@linbit.com>
Signed-off-by: Jens Axboe <jaxboe@fusionio.com>

diff --git a/drivers/block/drbd/drbd_main.c b/drivers/block/drbd/drbd_main.c
index 1fcf2d1..c978557 100644 (file)
--- a/drivers/block/drbd/drbd_main.c
+++ b/drivers/block/drbd/drbd_main.c
@@ -2272,9 +2272,9 @@ static int we_should_drop_the_connection(struct drbd_conf *mdev, struct socket *
  * with page_count == 0 or PageSlab.
  */
 static int _drbd_no_send_page(struct drbd_conf *mdev, struct page *page,
-                  int offset, size_t size)
+                  int offset, size_t size, unsigned msg_flags)
 {
-       int sent = drbd_send(mdev, mdev->data.socket, kmap(page) + offset, size, 0);
+       int sent = drbd_send(mdev, mdev->data.socket, kmap(page) + offset, size, msg_flags);
        kunmap(page);
        if (sent == size)
                mdev->send_cnt += size>>9;
@@ -2282,7 +2282,7 @@ static int _drbd_no_send_page(struct drbd_conf *mdev, struct page *page,
 }
 
 static int _drbd_send_page(struct drbd_conf *mdev, struct page *page,
-                   int offset, size_t size)
+                   int offset, size_t size, unsigned msg_flags)
 {
        mm_segment_t oldfs = get_fs();
        int sent, ok;
@@ -2295,14 +2295,15 @@ static int _drbd_send_page(struct drbd_conf *mdev, struct page *page,
         * __page_cache_release a page that would actually still be referenced
         * by someone, leading to some obscure delayed Oops somewhere else. */
        if (disable_sendpage || (page_count(page) < 1) || PageSlab(page))
-               return _drbd_no_send_page(mdev, page, offset, size);
+               return _drbd_no_send_page(mdev, page, offset, size, msg_flags);
 
+       msg_flags |= MSG_NOSIGNAL;
        drbd_update_congested(mdev);
        set_fs(KERNEL_DS);
        do {
                sent = mdev->data.socket->ops->sendpage(mdev->data.socket, page,
                                                        offset, len,
-                                                       MSG_NOSIGNAL);
+                                                       msg_flags);
                if (sent == -EAGAIN) {
                        if (we_should_drop_the_connection(mdev,
                                                          mdev->data.socket))
@@ -2331,9 +2332,11 @@ static int _drbd_send_bio(struct drbd_conf *mdev, struct bio *bio)
 {
        struct bio_vec *bvec;
        int i;
+       /* hint all but last page with MSG_MORE */
        __bio_for_each_segment(bvec, bio, i, 0) {
                if (!_drbd_no_send_page(mdev, bvec->bv_page,
-                                    bvec->bv_offset, bvec->bv_len))
+                                    bvec->bv_offset, bvec->bv_len,
+                                    i == bio->bi_vcnt -1 ? 0 : MSG_MORE))
                        return 0;
        }
        return 1;
@@ -2343,12 +2346,13 @@ static int _drbd_send_zc_bio(struct drbd_conf *mdev, struct bio *bio)
 {
        struct bio_vec *bvec;
        int i;
+       /* hint all but last page with MSG_MORE */
        __bio_for_each_segment(bvec, bio, i, 0) {
                if (!_drbd_send_page(mdev, bvec->bv_page,
-                                    bvec->bv_offset, bvec->bv_len))
+                                    bvec->bv_offset, bvec->bv_len,
+                                    i == bio->bi_vcnt -1 ? 0 : MSG_MORE))
                        return 0;
        }
-
        return 1;
 }
 
@@ -2356,9 +2360,11 @@ static int _drbd_send_zc_ee(struct drbd_conf *mdev, struct drbd_epoch_entry *e)
 {
        struct page *page = e->pages;
        unsigned len = e->size;
+       /* hint all but last page with MSG_MORE */
        page_chain_for_each(page) {
                unsigned l = min_t(unsigned, len, PAGE_SIZE);
-               if (!_drbd_send_page(mdev, page, 0, l))
+               if (!_drbd_send_page(mdev, page, 0, l,
+                               page_chain_next(page) ? MSG_MORE : 0))
                        return 0;
                len -= l;
        }
@@ -2438,11 +2444,11 @@ int drbd_send_dblock(struct drbd_conf *mdev, struct drbd_request *req)
        p.dp_flags = cpu_to_be32(dp_flags);
        set_bit(UNPLUG_REMOTE, &mdev->flags);
        ok = (sizeof(p) ==
-               drbd_send(mdev, mdev->data.socket, &p, sizeof(p), MSG_MORE));
+               drbd_send(mdev, mdev->data.socket, &p, sizeof(p), dgs ? MSG_MORE : 0));
        if (ok && dgs) {
                dgb = mdev->int_dig_out;
                drbd_csum_bio(mdev, mdev->integrity_w_tfm, req->master_bio, dgb);
-               ok = drbd_send(mdev, mdev->data.socket, dgb, dgs, MSG_MORE);
+               ok = drbd_send(mdev, mdev->data.socket, dgb, dgs, 0);
        }
        if (ok) {
                if (mdev->net_conf->wire_protocol == DRBD_PROT_A)
@@ -2491,11 +2497,11 @@ int drbd_send_block(struct drbd_conf *mdev, enum drbd_packets cmd,
                return 0;
 
        ok = sizeof(p) == drbd_send(mdev, mdev->data.socket, &p,
-                                       sizeof(p), MSG_MORE);
+                                       sizeof(p), dgs ? MSG_MORE : 0);
        if (ok && dgs) {
                dgb = mdev->int_dig_out;
                drbd_csum_ee(mdev, mdev->integrity_w_tfm, e, dgb);
-               ok = drbd_send(mdev, mdev->data.socket, dgb, dgs, MSG_MORE);
+               ok = drbd_send(mdev, mdev->data.socket, dgb, dgs, 0);
        }
        if (ok)
                ok = _drbd_send_zc_ee(mdev, e);