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[PULL,3/5] migration/block: limit the number of parallel I/O requests

Message ID 20180323202344.70640-4-dgilbert@redhat.com (mailing list archive)
State New, archived
Headers show

Commit Message

Dr. David Alan Gilbert March 23, 2018, 8:23 p.m. UTC 
From: Peter Lieven <pl@kamp.de>

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>
---
 migration/block.c | 2 ++
 1 file changed, 2 insertions(+)
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Patch

diff --git a/migration/block.c b/migration/block.c
index 5c03632257..03bbba61cb 100644
--- a/migration/block.c
+++ b/migration/block.c
@@ -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();