From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001

From: Stefan Reiter <s.reiter@proxmox.com>

Date: Wed, 9 Dec 2020 11:46:57 +0100

Subject: [PATCH] PVE: block/pbs: fast-path reads without allocation if

 possible

...and switch over to g_malloc/g_free while at it to align with other

QEMU code.

Tracing shows the fast-path is taken almost all the time, though not

100% so the slow one is still necessary.

Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>

Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>

---

 block/pbs.c | 17 ++++++++++++++---

 1 file changed, 14 insertions(+), 3 deletions(-)

diff --git a/block/pbs.c b/block/pbs.c

index 78dad0dcc4..ac54e816c0 100644

--- a/block/pbs.c

+++ b/block/pbs.c

@@ -200,7 +200,16 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,

     BDRVPBSState *s = bs->opaque;

     int ret;

     char *pbs_error = NULL;

-    uint8_t *buf = malloc(bytes);

+    uint8_t *buf;

+    bool inline_buf = true;

+

+    /* for single-buffer IO vectors we can fast-path the write directly to it */

+    if (qiov->niov == 1 && qiov->iov->iov_len >= bytes) {

+        buf = qiov->iov->iov_base;

+    } else {

+        inline_buf = false;

+        buf = g_malloc(bytes);

+    }

     ReadCallbackData rcb = {

         .co = qemu_coroutine_self(),

@@ -218,8 +227,10 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,

         return -EIO;

     }

-    qemu_iovec_from_buf(qiov, 0, buf, bytes);

-    free(buf);

+    if (!inline_buf) {

+        qemu_iovec_from_buf(qiov, 0, buf, bytes);

+        g_free(buf);

+    }

     return ret;

 }