debian/patches/pve/0044-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 ---
  15  block/pbs.c | 17 ++++++++++++++---
  16  1 file changed, 14 insertions(+), 3 deletions(-)
  17
  18 diff --git a/block/pbs.c b/block/pbs.c
  19 index 1481a2bfd1..fbf0d8d845 100644
  20 --- a/block/pbs.c
  21 +++ b/block/pbs.c
  22 @@ -200,7 +200,16 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,
  23      BDRVPBSState *s = bs->opaque;
  24      int ret;
  25      char *pbs_error = NULL;
  26 -    uint8_t *buf = malloc(bytes);
  27 +    uint8_t *buf;
  28 +    bool inline_buf = true;
  29 +
  30 +    /* for single-buffer IO vectors we can fast-path the write directly to it */
  31 +    if (qiov->niov == 1 && qiov->iov->iov_len >= bytes) {
  32 +        buf = qiov->iov->iov_base;
  33 +    } else {
  34 +        inline_buf = false;
  35 +        buf = g_malloc(bytes);
  36 +    }
  37
  38      ReadCallbackData rcb = {
  39          .co = qemu_coroutine_self(),
  40 @@ -218,8 +227,10 @@ static coroutine_fn int pbs_co_preadv(BlockDriverState *bs,
  41          return -EIO;
  42      }
  43
  44 -    qemu_iovec_from_buf(qiov, 0, buf, bytes);
  45 -    free(buf);
  46 +    if (!inline_buf) {
  47 +        qemu_iovec_from_buf(qiov, 0, buf, bytes);
  48 +        g_free(buf);
  49 +    }
  50
  51      return ret;
  52  }