scsi: target: Fix write perf due to unneeded throttling

The write back throttling (WBT) code checks if REQ_SYNC | REQ_IDLE is set
to determine if a write is O_DIRECT vs buffered. If the bits are not set
then it assumes it's a buffered write and will throttle LIO if we hit
certain metrics. LIO itself is not using the buffer cache and is doing
direct I/O, so this has us set the direct bits so we are not throttled.

When the initiator application is doing direct I/O this can greatly improve
performance. It depends on the backend device but we have seen where the
WBT code is throttling writes to only 20K IOPs with 4K I/Os when the device
can support 100K+.

Signed-off-by: Mike Christie <michael.christie@oracle.com>
Link: https://lore.kernel.org/r/20230817192902.346791-1-michael.christie@oracle.com
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>

diff --git a/drivers/target/target_core_iblock.c b/drivers/target/target_core_iblock.c
index 3d1b511ea284b0b71de47f99e830255cf8630284..5937a7ed6989c25b9c5963f63390f223f1642125 100644 (file)
--- a/drivers/target/target_core_iblock.c
+++ b/drivers/target/target_core_iblock.c
@@ -740,11 +740,16 @@ iblock_execute_rw(struct se_cmd *cmd, struct scatterlist *sgl, u32 sgl_nents,
 
        if (data_direction == DMA_TO_DEVICE) {
                struct iblock_dev *ib_dev = IBLOCK_DEV(dev);
+
+               /*
+                * Set bits to indicate WRITE_ODIRECT so we are not throttled
+                * by WBT.
+                */
+               opf = REQ_OP_WRITE | REQ_SYNC | REQ_IDLE;
                /*
                 * Force writethrough using REQ_FUA if a volatile write cache
                 * is not enabled, or if initiator set the Force Unit Access bit.
                 */
-               opf = REQ_OP_WRITE;
                miter_dir = SG_MITER_TO_SG;
                if (bdev_fua(ib_dev->ibd_bd)) {
                        if (cmd->se_cmd_flags & SCF_FUA)