On 10/21, Can Guo wrote: > On 2020-10-21 12:52, jaegeuk@xxxxxxxxxx wrote: > > On 10/21, Can Guo wrote: > > > On 2020-10-21 03:52, Jaegeuk Kim wrote: > > > > The below call stack prevents clk_gating at every IO completion. > > > > We can remove the condition, ufshcd_any_tag_in_use(), since > > > > clkgating_work > > > > will check it again. > > > > > > > > > > I think checking ufshcd_any_tag_in_use() in either ufshcd_release() or > > > gate_work() can break UFS clk gating's functionality. > > > > > > ufshcd_any_tag_in_use() was introduced to replace hba->lrb_in_use. > > > However, > > > they are not exactly same - ufshcd_any_tag_in_use() returns true if > > > any tag > > > assigned from block layer is still in use, but tags are released > > > asynchronously > > > (through block softirq), meaning it does not reflect the real > > > occupation of > > > UFS host. > > > That is after UFS host finishes all tasks, ufshcd_any_tag_in_use() > > > can still > > > return true. > > > > > > This change only removes the check of ufshcd_any_tag_in_use() in > > > ufshcd_release(), > > > but having the check of it in gate_work() can still prevent gating > > > from > > > happening. > > > The current change works for you maybe because the tags are release > > > before > > > hba->clk_gating.delay_ms expires, but if hba->clk_gating.delay_ms is > > > shorter > > > or > > > somehow block softirq is retarded, gate_work() may have chance to see > > > ufshcd_any_tag_in_use() > > > returns true. What do you think? > > > > I don't think this breaks clkgating, but fix the wrong condition check > > which > > prevented gate_work at all. As you mentioned, even if this schedules > > gate_work > > by racy conditions, gate_work will handle it as a last resort. > > > > If clocks cannot be gated after the last task is cleared from UFS host, then > clk gating > is broken, no? Assume UFS has completed the last task in its queue, as this > change says, > ufshcd_any_tag_in_use() is preventing ufshcd_release() from invoking > gate_work(). > Similarly, ufshcd_any_tag_in_use() can prevent gate_work() from doing its > real work - > disabling the clocks. Do you agree? > > if (hba->clk_gating.active_reqs > || hba->ufshcd_state != UFSHCD_STATE_OPERATIONAL > || ufshcd_any_tag_in_use(hba) || hba->outstanding_tasks > || hba->active_uic_cmd || hba->uic_async_done) > goto rel_lock; I see the point, but this happens only when clkgate_delay_ms is too short to give enough time for releasing tag. If it's correctly set, I think there'd be no problem, unless softirq was delayed by other RT threads which is just a corner case tho. > > Thanks, > > Can Guo. > > > > > > > Thanks, > > > > > > Can Guo. > > > > > > In __ufshcd_transfer_req_compl > > > Ihba->lrb_in_use is cleared immediately when UFS driver > > > finishes all tasks > > > > > > > ufshcd_complete_requests(struct ufs_hba *hba) > > > > ufshcd_transfer_req_compl() > > > > __ufshcd_transfer_req_compl() > > > > __ufshcd_release(hba) > > > > if (ufshcd_any_tag_in_use() == 1) > > > > return; > > > > ufshcd_tmc_handler(hba); > > > > blk_mq_tagset_busy_iter(); > > > > > > > > Cc: Alim Akhtar <alim.akhtar@xxxxxxxxxxx> > > > > Cc: Avri Altman <avri.altman@xxxxxxx> > > > > Cc: Can Guo <cang@xxxxxxxxxxxxxx> > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@xxxxxxxxxx> > > > > --- > > > > drivers/scsi/ufs/ufshcd.c | 2 +- > > > > 1 file changed, 1 insertion(+), 1 deletion(-) > > > > > > > > diff --git a/drivers/scsi/ufs/ufshcd.c b/drivers/scsi/ufs/ufshcd.c > > > > index b5ca0effe636..cecbd4ace8b4 100644 > > > > --- a/drivers/scsi/ufs/ufshcd.c > > > > +++ b/drivers/scsi/ufs/ufshcd.c > > > > @@ -1746,7 +1746,7 @@ static void __ufshcd_release(struct ufs_hba *hba) > > > > > > > > if (hba->clk_gating.active_reqs || hba->clk_gating.is_suspended || > > > > hba->ufshcd_state != UFSHCD_STATE_OPERATIONAL || > > > > - ufshcd_any_tag_in_use(hba) || hba->outstanding_tasks || > > > > + hba->outstanding_tasks || > > > > hba->active_uic_cmd || hba->uic_async_done) > > > > return;
