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authorJens Axboe <axboe@fb.com>2014-05-29 09:53:32 -0600
committerJens Axboe <axboe@fb.com>2014-05-29 09:53:32 -0600
commit05f1dd5315217398fc8d122bdee80f96a9f21274 (patch)
treef1decfafa5f0d974d2f9c707a514bf68b9e2cddb /include/linux/blkdev.h
parent4d92a9beb39d80a7d8ff7c04ae12a10290105ae5 (diff)
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block: add queue flag for disabling SG merging
If devices are not SG starved, we waste a lot of time potentially collapsing SG segments. Enough that 1.5% of the CPU time goes to this, at only 400K IOPS. Add a queue flag, QUEUE_FLAG_NO_SG_MERGE, which just returns the number of vectors in a bio instead of looping over all segments and checking for collapsible ones. Add a BLK_MQ_F_SG_MERGE flag so that drivers can opt-in on the sg merging, if they so desire. Signed-off-by: Jens Axboe <axboe@fb.com>
Diffstat (limited to 'include/linux/blkdev.h')
-rw-r--r--include/linux/blkdev.h1
1 files changed, 1 insertions, 0 deletions
diff --git a/include/linux/blkdev.h b/include/linux/blkdev.h
index 098304576d51..695b9fd41efe 100644
--- a/include/linux/blkdev.h
+++ b/include/linux/blkdev.h
@@ -510,6 +510,7 @@ struct request_queue {
#define QUEUE_FLAG_SAME_FORCE 18 /* force complete on same CPU */
#define QUEUE_FLAG_DEAD 19 /* queue tear-down finished */
#define QUEUE_FLAG_INIT_DONE 20 /* queue is initialized */
+#define QUEUE_FLAG_NO_SG_MERGE 21 /* don't attempt to merge SG segments*/
#define QUEUE_FLAG_DEFAULT ((1 << QUEUE_FLAG_IO_STAT) | \
(1 << QUEUE_FLAG_STACKABLE) | \
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