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=ham 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 58133C2D0A3 for ; Mon, 26 Oct 2020 06:19:55 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [23.128.96.18]) by mail.kernel.org (Postfix) with ESMTP id 0432720882 for ; Mon, 26 Oct 2020 06:19:54 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603693195; bh=ZMumJDxtizppcRhEvLccB7zDX1rEZFjVHF761knJgmg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:List-ID:From; b=vGJJVCF4eBw/+aSIeCo++2u4sdGHwz7DunTLY0QBdcqt1dngmp+uGT0M6QxuHBIyQ 3O+epRs5eXmySEmF9AkFvIAuEuKLoi9Y+v4zs3o8KHYSZ/JTj8LTHE1z4q9/ibsy5w SHmSrNJVqPwPV/WEo98biu5xBQF0NY5t2D2CZJeU= Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1770315AbgJZGTy (ORCPT ); Mon, 26 Oct 2020 02:19:54 -0400 Received: from mail.kernel.org ([198.145.29.99]:56708 "EHLO mail.kernel.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1770305AbgJZGTx (ORCPT ); Mon, 26 Oct 2020 02:19:53 -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 2D59520853; Mon, 26 Oct 2020 06:19:53 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/simple; d=kernel.org; s=default; t=1603693193; bh=ZMumJDxtizppcRhEvLccB7zDX1rEZFjVHF761knJgmg=; h=Date:From:To:Cc:Subject:References:In-Reply-To:From; b=pBd3JBzdGzJPLr0Nblc/VL0kcj3LHkF1QkK2ZIhWfuplBJJU6zXfQReJdXqsbkH5A FTzidI8lUc+CCE1gYIWuL3Dreay3Lbt8h4VzjbDFIDvd6JbiPFaK+8MA0MBeiA8C/c baHvrucRmV9WOodK/nw37PIg9KYtCfTQmQVqm6uc= Date: Sun, 25 Oct 2020 23:19:51 -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: <20201026061951.GB2517102@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> 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-kernel@vger.kernel.org On 10/26, Can Guo wrote: > 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. I think that can be fixed by a separate patch which controls delay_ms when user tries to change it from default 150 ms? > > 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;