On 11/30/2021 3:33 PM, Bart Van Assche wrote:
Remove the clock scaling lock from ufshcd_queuecommand() since it is a
performance bottleneck. Instead, use synchronize_rcu_expedited() 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 | 12 +++++++-----
drivers/scsi/ufs/ufshcd.h | 1 +
2 files changed, 8 insertions(+), 5 deletions(-)
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?
diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c
index c4cf5c4b4893..3e4c62c6f9d2 100644
--- a/drivers/scsi/ufs/ufshcd.c
+++ b/drivers/scsi/ufs/ufshcd.c
@@ -1196,6 +1196,13 @@ static int ufshcd_clock_scaling_prepare(struct ufs_hba *hba)
/* let's not get into low power until clock scaling is completed */
ufshcd_hold(hba, false);
+ /*
+ * Wait for ongoing ufshcd_queuecommand() calls. Calling
+ * synchronize_rcu_expedited() instead of synchronize_rcu() reduces the
+ * waiting time from milliseconds to microseconds.
+ */
+ synchronize_rcu_expedited();
+
out:
return ret;
}
@@ -2681,9 +2688,6 @@ 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 +2776,6 @@ 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
--
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