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scsi: target: Fix write perf due to unneeded throttling

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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>
This commit is contained in:
Mike Christie 2023-08-17 14:29:02 -05:00 committed by Martin K. Petersen
parent 19d7102a95
commit 84c073fd89
1 changed files with 6 additions and 1 deletions
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7
drivers/target/target_core_iblock.c
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@ -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)