On 12/1/21 3:33 PM, Asutosh Das (asd) wrote:
Hi Bart,
Say an IO (req1) has crossed the scsi_host_queue_ready() check but hasn't yet reached ufshcd_queuecommand() and DBR is 0.
ufshcd_clock_scaling_prepare() is invoked and completes and scaling proceeds to change the clocks and gear.
I wonder if the IO (req1) would be issued while scaling is in progress.
If so, do you think a check should be added in ufshcd_queuecommand() to see if scaling is in progress or if host is blocked?
How about using the patch below instead of patch 16/17 from this patch
series? The patch below should not trigger the race condition mentioned
above.
Thanks,
Bart.
Subject: [PATCH] scsi: ufs: Optimize the command queueing code
Remove the clock scaling lock from ufshcd_queuecommand() since it is a
performance bottleneck. Instead, wait until all budget_maps have cleared
to wait for ongoing ufshcd_queuecommand() calls.
Cc: Asutosh Das (asd) <asutoshd@xxxxxxxxxxxxxx>
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
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 c4cf5c4b4893..be679f2a97da 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;
+
+ shost_for_each_device(sdev, hba->host)
+ pending += sbitmap_weight(&sdev->budget_map);
+
+ 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 c3c2792f309f..411c6015bbfe 100644
--- a/drivers/scsi/ufs/ufshcd.h
+++ b/drivers/scsi/ufs/ufshcd.h
@@ -779,6 +779,7 @@ 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
