On 5/23/23 09:39, Adrian Hunter wrote:
On 18/05/23 01:23, Bart Van Assche wrote:
Prepare for adding code in ufshcd_queuecommand() that may sleep.
Signed-off-by: Bart Van Assche <bvanassche@xxxxxxx>
---
drivers/ufs/core/ufshcd.c | 1 +
1 file changed, 1 insertion(+)
diff --git a/drivers/ufs/core/ufshcd.c b/drivers/ufs/core/ufshcd.c
index 7ee150d67d49..993034ac1696 100644
--- a/drivers/ufs/core/ufshcd.c
+++ b/drivers/ufs/core/ufshcd.c
@@ -8756,6 +8756,7 @@ static const struct scsi_host_template ufshcd_driver_template = {
.max_host_blocked = 1,
.track_queue_depth = 1,
.skip_settle_delay = 1,
+ .queuecommand_may_block = true,
Shouldn't this only be for controllers that support
clock gating?
Hi Adrian,
The overhead of BLK_MQ_F_BLOCKING is small relative to the time required to
queue a UFS command so I think enabling BLK_MQ_F_BLOCKING for all UFS host
controllers is fine. BLK_MQ_F_BLOCKING causes the block layer to use SRCU
instead of RCU. The cost of the sleepable RCU primitives is dominated by
the memory barrier (smp_mb()) in the srcu_read_lock() and srcu_read_unlock()
calls. From kernel/rcu/srcutree.c:
int __srcu_read_lock(struct srcu_struct *ssp)
{
int idx;
idx = READ_ONCE(ssp->srcu_idx) & 0x1;
this_cpu_inc(ssp->sda->srcu_lock_count[idx].counter);
smp_mb(); /* B */ /* Avoid leaking the critical section. */
return idx;
}
EXPORT_SYMBOL_GPL(__srcu_read_lock);
void __srcu_read_unlock(struct srcu_struct *ssp, int idx)
{
smp_mb(); /* C */ /* Avoid leaking the critical section. */
this_cpu_inc(ssp->sda->srcu_unlock_count[idx].counter);
}
EXPORT_SYMBOL_GPL(__srcu_read_unlock);
The rcu_read_lock() and rcu_read_lock() implementations do not call
smp_mb() as one can see in include/linux/rcupdate.h:
static inline void __rcu_read_lock(void)
{
preempt_disable();
}
static inline void __rcu_read_unlock(void)
{
preempt_enable();
if (IS_ENABLED(CONFIG_RCU_STRICT_GRACE_PERIOD))
rcu_read_unlock_strict();
}
Thanks,
Bart.
