SCSI currently uses an atomic variable to track queue depth for each
attached device. The queue depth depends on many factors such as transport
type and device implementation. In addition, the SCSI device queue depth is
not a static entity but changes over time as a result of congestion
management.
While blk-mq currently tracks queue depth for each hctx, it can't easily be
changed to accommodate the SCSI per-device requirement.
The current approach of using an atomic variable doesn't scale well when
there are lots of CPU cores and the disk is very fast. IOPS can be
substantially impacted by the atomic in the hot path.
Replace the atomic variable sdev->device_busy with an sbitmap for tracking
the SCSI device queue depth.
It has been observed that IOPS is improved ~30% by this patchset in the
following test:
1) test machine(32 logical CPU cores)
Thread(s) per core: 2
Core(s) per socket: 8
Socket(s): 2
NUMA node(s): 2
Model name: Intel(R) Xeon(R) Silver 4110 CPU @ 2.10GHz
2) setup scsi_debug:
modprobe scsi_debug virtual_gb=128 max_luns=1 submit_queues=32 delay=0 max_queue=256
3) fio script:
fio --rw=randread --size=128G --direct=1 --ioengine=libaio --iodepth=2048 \
--numjobs=32 --bs=4k --group_reporting=1 --group_reporting=1 --runtime=60 \
--loops=10000 --name=job1 --filename=/dev/sdN
[mkp: fix device_busy reference in mpt3sas]
Link: https://lore.kernel.org/r/20210122023317.687987-14-ming.lei@redhat.com
Link: https://lore.kernel.org/linux-block/20200119071432.18558-6-ming.lei@redhat.com/
Cc: Omar Sandoval <osandov@fb.com>
Cc: Kashyap Desai <kashyap.desai@broadcom.com>
Cc: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Cc: Ewan D. Milne <emilne@redhat.com>
Cc: Hannes Reinecke <hare@suse.de>
Tested-by: Sumanesh Samanta <sumanesh.samanta@broadcom.com>
Reviewed-by: Hannes Reinecke <hare@suse.de>
Signed-off-by: Ming Lei <ming.lei@redhat.com>
Signed-off-by: Martin K. Petersen <martin.petersen@oracle.com>
* IOs on the target device is >=8.
*/
- if (atomic_read(&scmd->device->device_busy) >
- MPT3SAS_DEVICE_HIGH_IOPS_DEPTH)
+ if (scsi_device_busy(scmd->device) > MPT3SAS_DEVICE_HIGH_IOPS_DEPTH)
return base_mod64((
atomic64_add_return(1, &ioc->high_iops_outstanding) /
MPT3SAS_HIGH_IOPS_BATCH_COUNT),
/*
* 1024 is big enough for saturating the fast scsi LUN now
*/
-static int scsi_device_max_queue_depth(struct scsi_device *sdev)
+int scsi_device_max_queue_depth(struct scsi_device *sdev)
{
return max_t(int, sdev->host->can_queue, 1024);
}
if (sdev->request_queue)
blk_set_queue_depth(sdev->request_queue, depth);
+ sbitmap_resize(&sdev->budget_map, sdev->queue_depth);
+
return sdev->queue_depth;
}
EXPORT_SYMBOL(scsi_change_queue_depth);
if (starget->can_queue > 0)
atomic_dec(&starget->target_busy);
- atomic_dec(&sdev->device_busy);
+ sbitmap_put(&sdev->budget_map, cmd->budget_token);
cmd->budget_token = -1;
}
}
/*
- * scsi_dev_queue_ready: if we can send requests to sdev, return 1 else
- * return 0.
- *
- * Called with the queue_lock held.
+ * scsi_dev_queue_ready: if we can send requests to sdev, assign one token
+ * and return the token else return -1.
*/
static inline int scsi_dev_queue_ready(struct request_queue *q,
struct scsi_device *sdev)
{
- unsigned int busy;
+ int token;
- busy = atomic_inc_return(&sdev->device_busy) - 1;
+ token = sbitmap_get(&sdev->budget_map);
if (atomic_read(&sdev->device_blocked)) {
- if (busy)
+ if (token < 0)
+ goto out;
+
+ if (scsi_device_busy(sdev) > 1)
goto out_dec;
/*
"unblocking device at zero depth\n"));
}
- if (busy >= sdev->queue_depth)
- goto out_dec;
-
- return 1;
+ return token;
out_dec:
- atomic_dec(&sdev->device_busy);
- return 0;
+ if (token >= 0)
+ sbitmap_put(&sdev->budget_map, token);
+out:
+ return -1;
}
/*
{
struct scsi_device *sdev = q->queuedata;
- atomic_dec(&sdev->device_busy);
+ sbitmap_put(&sdev->budget_map, budget_token);
}
static int scsi_mq_get_budget(struct request_queue *q)
{
struct scsi_device *sdev = q->queuedata;
+ int token = scsi_dev_queue_ready(q, sdev);
- if (scsi_dev_queue_ready(q, sdev))
- return 0;
+ if (token >= 0)
+ return token;
atomic_inc(&sdev->restarts);
#include <linux/device.h>
#include <linux/async.h>
#include <scsi/scsi_device.h>
+#include <linux/sbitmap.h>
struct request_queue;
struct request;
static inline void scsi_dh_release_device(struct scsi_device *sdev) { }
#endif
+extern int scsi_device_max_queue_depth(struct scsi_device *sdev);
+
/*
* internal scsi timeout functions: for use by mid-layer and transport
* classes.
static struct scsi_device *scsi_alloc_sdev(struct scsi_target *starget,
u64 lun, void *hostdata)
{
+ unsigned int depth;
struct scsi_device *sdev;
int display_failure_msg = 1, ret;
struct Scsi_Host *shost = dev_to_shost(starget->dev.parent);
WARN_ON_ONCE(!blk_get_queue(sdev->request_queue));
sdev->request_queue->queuedata = sdev;
- scsi_change_queue_depth(sdev, sdev->host->cmd_per_lun ?
- sdev->host->cmd_per_lun : 1);
+ depth = sdev->host->cmd_per_lun ?: 1;
+
+ /*
+ * Use .can_queue as budget map's depth because we have to
+ * support adjusting queue depth from sysfs. Meantime use
+ * default device queue depth to figure out sbitmap shift
+ * since we use this queue depth most of times.
+ */
+ if (sbitmap_init_node(&sdev->budget_map,
+ scsi_device_max_queue_depth(sdev),
+ sbitmap_calculate_shift(depth),
+ GFP_KERNEL, sdev->request_queue->node,
+ false, true)) {
+ put_device(&starget->dev);
+ kfree(sdev);
+ goto out;
+ }
+
+ scsi_change_queue_depth(sdev, depth);
scsi_sysfs_device_initialize(sdev);
scsi_attach_vpd(sdev);
sdev->max_queue_depth = sdev->queue_depth;
+ WARN_ON_ONCE(sdev->max_queue_depth > sdev->budget_map.depth);
sdev->sdev_bflags = *bflags;
/*
/* NULL queue means the device can't be used */
sdev->request_queue = NULL;
+ sbitmap_free(&sdev->budget_map);
+
mutex_lock(&sdev->inquiry_mutex);
vpd_pg0 = rcu_replace_pointer(sdev->vpd_pg0, vpd_pg0,
lockdep_is_held(&sdev->inquiry_mutex));
#include <linux/blkdev.h>
#include <scsi/scsi.h>
#include <linux/atomic.h>
+#include <linux/sbitmap.h>
struct device;
struct request_queue;
struct list_head siblings; /* list of all devices on this host */
struct list_head same_target_siblings; /* just the devices sharing same target id */
- atomic_t device_busy; /* commands actually active on LLDD */
+ struct sbitmap budget_map;
atomic_t device_blocked; /* Device returned QUEUE_FULL. */
atomic_t restarts;
static inline int scsi_device_busy(struct scsi_device *sdev)
{
- return atomic_read(&sdev->device_busy);
+ return sbitmap_weight(&sdev->budget_map);
}
#define MODULE_ALIAS_SCSI_DEVICE(type) \
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