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block, block-backend: write some hot coroutine wrappers by hand

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The introduction of the graph lock is causing blk_get_geometry, a hot function
used in the I/O path, to create a coroutine.  However, the only part that really
needs to run in coroutine context is the call to bdrv_co_refresh_total_sectors,
which in turn only happens in the rare case of host CD-ROM devices.

So, write by hand the three wrappers on the path from blk_co_get_geometry to
bdrv_co_refresh_total_sectors, so that the coroutine wrapper is only created
if bdrv_nb_sectors actually calls bdrv_refresh_total_sectors.

Reported-by: Stefan Hajnoczi <stefanha@redhat.com>
Signed-off-by: Paolo Bonzini <pbonzini@redhat.com>
Message-Id: <20230407153303.391121-9-pbonzini@redhat.com>
Reviewed-by: Kevin Wolf <kwolf@redhat.com>
Signed-off-by: Kevin Wolf <kwolf@redhat.com>
This commit is contained in:
Paolo Bonzini 2023-04-07 17:33:03 +02:00 • committed by Kevin Wolf
parent 9ed98cae15
commit 81f730d4d0
4 changed files with 52 additions and 4 deletions
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27
block/block-backend.c
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@ -1629,6 +1629,23 @@ int64_t coroutine_fn blk_co_nb_sectors(BlockBackend *blk)
}
}
/*
* This wrapper is written by hand because this function is in the hot I/O path,
* via blk_get_geometry.
*/
int64_t coroutine_mixed_fn blk_nb_sectors(BlockBackend *blk)
{
BlockDriverState *bs = blk_bs(blk);
IO_CODE();
if (!bs) {
return -ENOMEDIUM;
} else {
return bdrv_nb_sectors(bs);
}
}
/* return 0 as number of sectors if no device present or error */
void coroutine_fn blk_co_get_geometry(BlockBackend *blk,
uint64_t *nb_sectors_ptr)
@ -1637,6 +1654,16 @@ void coroutine_fn blk_co_get_geometry(BlockBackend *blk,
*nb_sectors_ptr = ret < 0 ? 0 : ret;
}
/*
* This wrapper is written by hand because this function is in the hot I/O path.
*/
void coroutine_mixed_fn blk_get_geometry(BlockBackend *blk,
uint64_t *nb_sectors_ptr)
{
int64_t ret = blk_nb_sectors(blk);
*nb_sectors_ptr = ret < 0 ? 0 : ret;
}
BlockAIOCB *blk_aio_preadv(BlockBackend *blk, int64_t offset,
QEMUIOVector *qiov, BdrvRequestFlags flags,
BlockCompletionFunc *cb, void *opaque)