debian/patches/pve/0045-PVE-block-pbs-fast-path-reads-without-allocation-if-.patch

   1 From 0000000000000000000000000000000000000000 Mon Sep 17 00:00:00 2001
   2 From: Stefan Reiter <s.reiter@proxmox.com>
   3 Date: Wed, 9 Dec 2020 11:46:57 +0100
   4 Subject: [PATCH] PVE: block/pbs: fast-path reads without allocation if
   5  possible
   6
   7 ...and switch over to g_malloc/g_free while at it to align with other
   8 QEMU code.
   9
  10 Tracing shows the fast-path is taken almost all the time, though not
  11 100% so the slow one is still necessary.
  12
  13 Signed-off-by: Stefan Reiter <s.reiter@proxmox.com>
  14 Signed-off-by: Thomas Lamprecht <t.lamprecht@proxmox.com>
  15 ---
  16  block/pbs.c | 17 ++++++++++++++---
  17  1 file changed, 14 insertions(+), 3 deletions(-)
  18
  19 diff --git a/block/pbs.c b/block/pbs.c
  20 index 9d1f1f39d4..ce9a870885 100644
  21 --- a/block/pbs.c
  22 +++ b/block/pbs.c
  23 @@ -200,7 +200,16 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,
  24      BDRVPBSState *s = bs->opaque;
  25      int ret;
  26      char *pbs_error = NULL;
  27 -    uint8_t *buf = malloc(bytes);
  28 +    uint8_t *buf;
  29 +    bool inline_buf = true;
  30 +
  31 +    /* for single-buffer IO vectors we can fast-path the write directly to it */
  32 +    if (qiov->niov == 1 && qiov->iov->iov_len >= bytes) {
  33 +        buf = qiov->iov->iov_base;
  34 +    } else {
  35 +        inline_buf = false;
  36 +        buf = g_malloc(bytes);
  37 +    }
  38
  39      if (offset < 0 || bytes < 0) {
  40          fprintf(stderr, "unexpected negative 'offset' or 'bytes' value!\n");
  41 @@ -223,8 +232,10 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,
  42          return -EIO;
  43      }
  44
  45 -    qemu_iovec_from_buf(qiov, 0, buf, bytes);
  46 -    free(buf);
  47 +    if (!inline_buf) {
  48 +        qemu_iovec_from_buf(qiov, 0, buf, bytes);
  49 +        g_free(buf);
  50 +    }
  51
  52      return 0;
  53  }