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Mon, 26 Oct 2020 03:12:02 GMT Received: by smtp.codeaurora.org (Postfix, from userid 1001) id AACF9C433C9; Mon, 26 Oct 2020 03:12:01 +0000 (UTC) Received: from mail.codeaurora.org (localhost.localdomain [127.0.0.1]) (using TLSv1 with cipher ECDHE-RSA-AES256-SHA (256/256 bits)) (No client certificate requested) (Authenticated sender: cang) by smtp.codeaurora.org (Postfix) with ESMTPSA id 4243EC433CB; Mon, 26 Oct 2020 03:12:00 +0000 (UTC) MIME-Version: 1.0 Date: Mon, 26 Oct 2020 11:12:00 +0800 From: Can Guo To: Jaegeuk Kim In-Reply-To: <20201022201825.GA3329812@google.com> References: <20201020195258.2005605-1-jaegeuk@kernel.org> <20201020195258.2005605-6-jaegeuk@kernel.org> <2a8ecc4185b3a5411077f4e3fc66000f@codeaurora.org> <20201021045213.GB3004521@google.com> <20201022201825.GA3329812@google.com> Message-ID: X-Sender: cang@codeaurora.org User-Agent: Roundcube Webmail/1.3.9 X-Headers-End: 1kWtKL-00793l-KQ Subject: Re: [f2fs-dev] [PATCH v2 5/5] scsi: ufs: fix clkgating on/off correctly X-BeenThere: linux-f2fs-devel@lists.sourceforge.net X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-scsi@vger.kernel.org, linux-kernel@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, Avri Altman , Alim Akhtar , kernel-team@android.com Content-Transfer-Encoding: 7bit Content-Type: text/plain; charset="us-ascii"; Format="flowed" Errors-To: linux-f2fs-devel-bounces@lists.sourceforge.net On 2020-10-23 08:53, Jaegeuk Kim wrote: > 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. > Yes, we are fixing corner cases, aren't we? I thought you would like to address it since you are fixing clk gating. Regards, Can Guo. >> >> 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 >> > > > Cc: Avri Altman >> > > > Cc: Can Guo >> > > > Signed-off-by: Jaegeuk Kim >> > > > --- >> > > > 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