From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: X-Spam-Checker-Version: SpamAssassin 3.4.0 (2014-02-07) on aws-us-west-2-korg-lkml-1.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-10.1 required=3.0 tests=BAYES_00,DKIMWL_WL_HIGH, DKIM_SIGNED,DKIM_VALID,DKIM_VALID_AU,INCLUDES_PATCH,MAILING_LIST_MULTI, SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS,URIBL_BLOCKED autolearn=unavailable autolearn_force=no version=3.4.0 Received: from mail.kernel.org (mail.kernel.org [198.145.29.99]) by smtp.lore.kernel.org (Postfix) with ESMTP id 1ACBEC55179 for ; Fri, 23 Oct 2020 00:53:46 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id B15EA24650 for ; Fri, 23 Oct 2020 00:53:45 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603414425; bh=H7BSQBTeld9dIe7VZCTb35eY55DnK0do+KNc0IrodUk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=aWxQ36PZtnLc7pJj7PBR2BQWJgB6v8vIlGi+dpeklXE1c/xFeJH3FTjM8fGyetE/f lCRE46W8oMHTUPImh/Qb3K7XIh5mVK0dIOI6lPY1idNOpn9VX6M1Ej1J1lKTuMOSQY PVtRJHMnWop4y7CyrLQWCeG9B3QqvYcqu9CIorZU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S374147AbgJWAxm (ORCPT ); Thu, 22 Oct 2020 20:53:42 -0400 Received: from mail.kernel.org ([198.145.29.99]:39894 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S2900356AbgJWAxm (ORCPT ); Thu, 22 Oct 2020 20:53:42 -0400 Received: from google.com (unknown [104.132.1.66]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPSA id F32D124630; Fri, 23 Oct 2020 00:53:40 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603414421; bh=H7BSQBTeld9dIe7VZCTb35eY55DnK0do+KNc0IrodUk=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=KiTUVx2RfDCA18tppCH65YVG0kmUIN5GraBTZpBsOQPBOViAOA9Juk8PIjQi+atQN 61CEirviHxZKb4fqSblB6roOvMSesxvdvLhFKL8z+r541lpvuGJeriXLlqXR21MXLB 7PLtXs+iuiy+ZJ0isFZV/Uz6wqy8jkvpQkou4eKM= Date: Thu, 22 Oct 2020 17:53:39 -0700 From: Jaegeuk Kim To: Can Guo Cc: linux-kernel@vger.kernel.org, linux-scsi@vger.kernel.org, linux-f2fs-devel@lists.sourceforge.net, kernel-team@android.com, Alim Akhtar , Avri Altman Subject: Re: [PATCH v2 5/5] scsi: ufs: fix clkgating on/off correctly Message-ID: <20201022201825.GA3329812@google.com> References: <20201020195258.2005605-1-jaegeuk@kernel.org> <20201020195258.2005605-6-jaegeuk@kernel.org> <2a8ecc4185b3a5411077f4e3fc66000f@codeaurora.org> <20201021045213.GB3004521@google.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Precedence: bulk List-ID: X-Mailing-List: linux-scsi@vger.kernel.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 > > > > 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;