On 12/6/2021 2:41 PM, Asutosh Das (asd) wrote:
On 12/3/2021 3:19 PM, Bart Van Assche wrote:
Remove the clock scaling lock from ufshcd_queuecommand() since it is a
performance bottleneck. Instead check the SCSI device budget bitmaps in
the code that waits for ongoing ufshcd_queuecommand() calls. A bit is
set in sdev->budget_map just before scsi_queue_rq() is called and a bit
is cleared from that bitmap if scsi_queue_rq() does not submit the
request or after the request has finished. See also the
blk_mq_{get,put}_dispatch_budget() calls in the block layer.
There is no risk for a livelock since the block layer delays queue
reruns if queueing a request fails because the SCSI host has been
blocked.
Cc: Asutosh Das (asd) <asutoshd@xxxxxxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
Reviewed-by: Asutosh Das <asutoshd@xxxxxxxxxxxxxx>
Replying to my own mail.
Hi Bart,
drivers/scsi/ufs/ufshcd.c | 33 +++++++++++++++++++++++----------
drivers/scsi/ufs/ufshcd.h | 1 +
2 files changed, 24 insertions(+), 10 deletions(-)
diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index 9f0a1f637030..650dddf960c2 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1070,13 +1070,31 @@ static bool
ufshcd_is_devfreq_scaling_required(struct ufs_hba *hba,
return false;
}
+/*
+ * Determine the number of pending commands by counting the bits in
the SCSI
+ * device budget maps. This approach has been selected because a bit
is set in
+ * the budget map before scsi_host_queue_ready() checks the
host_self_blocked
+ * flag. The host_self_blocked flag can be modified by calling
+ * scsi_block_requests() or scsi_unblock_requests().
+ */
+static u32 ufshcd_pending_cmds(struct ufs_hba *hba)
+{
+ struct scsi_device *sdev;
+ u32 pending = 0;
+
+ shost_for_each_device(sdev, hba->host)
+ pending += sbitmap_weight(&sdev->budget_map);
+
I was porting this change to my downstream code and it occurred to me
that in a high IO rate scenario it's possible that bits in the
budget_map may be set even when that particular IO may not be issued to
driver. So there would unnecessary waiting for that to be cleared.
Do you think it's possible?
I think we should wait only for requests which are already started.
e.g. blk_mq_tagset_busy_iter() ?
PLMK your thoughts on this.
+ return pending;
+}
+
static int ufshcd_wait_for_doorbell_clr(struct ufs_hba *hba,
u64 wait_timeout_us)
{
unsigned long flags;
int ret = 0;
u32 tm_doorbell;
- u32 tr_doorbell;
+ u32 tr_pending;
bool timeout = false, do_last_check = false;
ktime_t start;
@@ -1094,8 +1112,8 @@ static int ufshcd_wait_for_doorbell_clr(struct
ufs_hba *hba,
}
tm_doorbell = ufshcd_readl(hba, REG_UTP_TASK_REQ_DOOR_BELL);
- tr_doorbell = ufshcd_readl(hba, REG_UTP_TRANSFER_REQ_DOOR_BELL);
- if (!tm_doorbell && !tr_doorbell) {
+ tr_pending = ufshcd_pending_cmds(hba);
+ if (!tm_doorbell && !tr_pending) {
timeout = false;
break;
} else if (do_last_check) {
@@ -1115,12 +1133,12 @@ static int ufshcd_wait_for_doorbell_clr(struct
ufs_hba *hba,
do_last_check = true;
}
spin_lock_irqsave(hba->host->host_lock, flags);
- } while (tm_doorbell || tr_doorbell);
+ } while (tm_doorbell || tr_pending);
if (timeout) {
dev_err(hba->dev,
"%s: timedout waiting for doorbell to clear (tm=0x%x,
tr=0x%x)\n",
- __func__, tm_doorbell, tr_doorbell);
+ __func__, tm_doorbell, tr_pending);
ret = -EBUSY;
}
out:
@@ -2681,9 +2699,6 @@ static int ufshcd_queuecommand(struct Scsi_Host
*host, struct scsi_cmnd *cmd)
WARN_ONCE(tag < 0, "Invalid tag %d\n", tag);
- if (!down_read_trylock(&hba->clk_scaling_lock))
- return SCSI_MLQUEUE_HOST_BUSY;
-
/*
* Allows the UFS error handler to wait for prior
ufshcd_queuecommand()
* calls.
@@ -2772,8 +2787,6 @@ static int ufshcd_queuecommand(struct Scsi_Host
*host, struct scsi_cmnd *cmd)
out:
rcu_read_unlock();
- up_read(&hba->clk_scaling_lock);
-
if (ufs_trigger_eh()) {
unsigned long flags;
diff --git a/drivers/scsi/ufs/ufshcd.h b/drivers/scsi/ufs/ufshcd.h
index 8e942762e668..88c20f3608c2 100644
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -778,6 +778,7 @@ struct ufs_hba_monitor {
* @clk_list_head: UFS host controller clocks list node head
* @pwr_info: holds current power mode
* @max_pwr_info: keeps the device max valid pwm
+ * @clk_scaling_lock: used to serialize device commands and clock
scaling
* @desc_size: descriptor sizes reported by device
* @urgent_bkops_lvl: keeps track of urgent bkops level for device
* @is_urgent_bkops_lvl_checked: keeps track if the urgent bkops
level for
--
The Qualcomm Innovation Center, Inc. is a member of the Code Aurora Forum,
Linux Foundation Collaborative Project
