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migration/block: limit the number of parallel I/O requests 

the current implementation submits up to 512 I/O requests in parallel
which is much to high especially for a background task.
This patch adds a maximum limit of 16 I/O requests that can
be submitted in parallel to avoid monopolizing the I/O device.

Signed-off-by: Peter Lieven <pl@kamp.de>
Message-Id: <1520507908-16743-5-git-send-email-pl@kamp.de>
Reviewed-by: Juan Quintela <quintela@redhat.com>
Signed-off-by: Dr. David Alan Gilbert <dgilbert@redhat.com>
This commit is contained in:
Peter Lieven 2018-03-08 12:18:27 +01:00 committed by Dr. David Alan Gilbert
parent e8a0f2f9a1
commit 44815334e1
1 changed files with 2 additions and 0 deletions
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migration/block.c
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@ -37,6 +37,7 @@
#define MAX_IS_ALLOCATED_SEARCH (65536 * BDRV_SECTOR_SIZE)
#define MAX_IO_BUFFERS 512
#define MAX_PARALLEL_IO 16
//#define DEBUG_BLK_MIGRATION
@ -775,6 +776,7 @@ static int block_save_iterate(QEMUFile *f, void *opaque)
while ((block_mig_state.submitted +
block_mig_state.read_done) * BLOCK_SIZE <
qemu_file_get_rate_limit(f) &&
block_mig_state.submitted < MAX_PARALLEL_IO &&
(block_mig_state.submitted + block_mig_state.read_done) <
MAX_IO_BUFFERS) {
blk_mig_unlock();