Re: [PATCH 10/11] scsi: ufs: Optimize the command queueing code
From: Adrian Hunter <adrian.hunter@intel.com>
Date: 2021-11-10 08:04:24
On 10/11/2021 02:44, Bart Van Assche wrote:
Remove the clock scaling lock from ufshcd_queuecommand() since it is a performance bottleneck. As requested by Asutosh Das, change the behavior of ufshcd_clock_scaling_prepare() from waiting until all pending commands have finished into quiescing request queues. Insert a rcu_read_lock() / rcu_read_unlock() pair in ufshcd_queuecommand() and also in __ufshcd_issue_tm_cmd(). Use synchronize_rcu_expedited() to wait for ongoing command and TMF queueing. Signed-off-by: Bart Van Assche <bvanassche@acm.org> --- drivers/scsi/ufs/ufshcd.c | 121 +++++++++++++------------------------- drivers/scsi/ufs/ufshcd.h | 1 + 2 files changed, 42 insertions(+), 80 deletions(-)
<SNIP>
quoted hunk ↗ jump to hunk
@@ -2698,8 +2653,11 @@ 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 ufshcd_clock_scaling_prepare() and also the UFS error handler + * to wait for prior ufshcd_queuecommand() calls. + */ + rcu_read_lock();
The improvement to flush/drain ufshcd_queuecommand() via RCU should be a separate patch because it is not dependent on the other changes. <SNIP>