From: Jaegeuk Kim <jaegeuk@kernel.org> To: Can Guo <cang@codeaurora.org> Cc: linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com, Alim Akhtar <alim.akhtar@samsung.com>, Avri Altman <avri.altman@wdc.com> Subject: Re: [PATCH v2 5/5] scsi: ufs: fix clkgating on/off correctly Date: Thu, 22 Oct 2020 17:53:39 -0700 [thread overview] Message-ID: <20201022201825.GA3329812@google.com> (raw) In-Reply-To: <e3e58a89474d23f1b9446fe2e38a7426@codeaurora.org> On 10/21, Can Guo wrote: > On 2020-10-21 12:52, jaegeuk@kernel.org 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@samsung.com> > > > > Cc: Avri Altman <avri.altman@wdc.com> > > > > Cc: Can Guo <cang@codeaurora.org> > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> > > > > --- > > > > 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;
WARNING: multiple messages have this Message-ID (diff)
From: Jaegeuk Kim <jaegeuk@kernel.org> To: Can Guo <cang@codeaurora.org> Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Avri Altman <avri.altman@wdc.com>, Alim Akhtar <alim.akhtar@samsung.com>, kernel-team@android.com Subject: Re: [f2fs-dev] [PATCH v2 5/5] scsi: ufs: fix clkgating on/off correctly Date: Thu, 22 Oct 2020 17:53:39 -0700 [thread overview] Message-ID: <20201022201825.GA3329812@google.com> (raw) In-Reply-To: <e3e58a89474d23f1b9446fe2e38a7426@codeaurora.org> On 10/21, Can Guo wrote: > On 2020-10-21 12:52, jaegeuk@kernel.org 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@samsung.com> > > > > Cc: Avri Altman <avri.altman@wdc.com> > > > > Cc: Can Guo <cang@codeaurora.org> > > > > Signed-off-by: Jaegeuk Kim <jaegeuk@kernel.org> > > > > --- > > > > 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; _______________________________________________ Linux-f2fs-devel mailing list Linux-f2fs-devel@lists.sourceforge.net https://lists.sourceforge.net/lists/listinfo/linux-f2fs-devel
next prev parent reply other threads:[~2020-10-23 0:53 UTC|newest] Thread overview: 34+ messages / expand[flat|nested] mbox.gz Atom feed top 2020-10-20 19:52 propose some UFS fixes Jaegeuk Kim 2020-10-20 19:52 ` [f2fs-dev] " Jaegeuk Kim 2020-10-20 19:52 ` [PATCH v2 1/5] scsi: ufs: atomic update for clkgating_enable Jaegeuk Kim 2020-10-20 19:52 ` [f2fs-dev] " Jaegeuk Kim 2020-10-21 2:05 ` Can Guo 2020-10-21 2:05 ` [f2fs-dev] " Can Guo 2020-10-21 4:41 ` jaegeuk 2020-10-21 4:41 ` [f2fs-dev] " jaegeuk 2020-10-20 19:52 ` [PATCH v2 2/5] scsi: ufs: clear UAC for FFU and RPMB LUNs Jaegeuk Kim 2020-10-20 19:52 ` [f2fs-dev] " Jaegeuk Kim 2020-10-20 19:52 ` [PATCH v2 3/5] scsi: ufs: use WQ_HIGHPRI for gating work Jaegeuk Kim 2020-10-20 19:52 ` [f2fs-dev] " Jaegeuk Kim 2020-10-21 0:57 ` Can Guo 2020-10-21 0:57 ` [f2fs-dev] " Can Guo 2020-10-21 4:52 ` jaegeuk 2020-10-21 4:52 ` [f2fs-dev] " jaegeuk 2020-10-20 19:52 ` [PATCH v2 4/5] scsi: add more contexts in the ufs tracepoints Jaegeuk Kim 2020-10-20 19:52 ` [f2fs-dev] " Jaegeuk Kim 2020-10-20 19:52 ` [PATCH v2 5/5] scsi: ufs: fix clkgating on/off correctly Jaegeuk Kim 2020-10-20 19:52 ` [f2fs-dev] " Jaegeuk Kim 2020-10-21 2:00 ` Can Guo 2020-10-21 2:00 ` [f2fs-dev] " Can Guo 2020-10-21 4:52 ` jaegeuk 2020-10-21 4:52 ` [f2fs-dev] " jaegeuk 2020-10-21 6:05 ` Can Guo 2020-10-21 6:05 ` [f2fs-dev] " Can Guo 2020-10-23 0:53 ` Jaegeuk Kim [this message] 2020-10-23 0:53 ` Jaegeuk Kim 2020-10-26 3:12 ` Can Guo 2020-10-26 3:12 ` [f2fs-dev] " Can Guo 2020-10-26 6:19 ` Jaegeuk Kim 2020-10-26 6:19 ` [f2fs-dev] " Jaegeuk Kim 2020-10-26 18:47 ` asutoshd 2020-10-26 18:47 ` [f2fs-dev] " asutoshd
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