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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 51993C43331 for ; Fri, 3 Apr 2020 06:22:36 +0000 (UTC) Received: from vger.kernel.org (vger.kernel.org [209.132.180.67]) by mail.kernel.org (Postfix) with ESMTP id 1FEE320721 for ; Fri, 3 Apr 2020 06:22:36 +0000 (UTC) Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S2388022AbgDCGWe (ORCPT ); Fri, 3 Apr 2020 02:22:34 -0400 Received: from mx0b-001b2d01.pphosted.com ([148.163.158.5]:26910 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S1729423AbgDCGWe (ORCPT ); Fri, 3 Apr 2020 02:22:34 -0400 Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 0335dSnM087477; Fri, 3 Apr 2020 02:22:25 -0400 Received: from ppma03wdc.us.ibm.com (ba.79.3fa9.ip4.static.sl-reverse.com [169.63.121.186]) by mx0b-001b2d01.pphosted.com with ESMTP id 305s8309m9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 03 Apr 2020 02:22:25 -0400 Received: from pps.filterd (ppma03wdc.us.ibm.com [127.0.0.1]) by ppma03wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id 0336LfaW001775; Fri, 3 Apr 2020 06:22:24 GMT Received: from b01cxnp22036.gho.pok.ibm.com (b01cxnp22036.gho.pok.ibm.com [9.57.198.26]) by ppma03wdc.us.ibm.com with ESMTP id 301x776wcd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 03 Apr 2020 06:22:24 +0000 Received: from b01ledav002.gho.pok.ibm.com (b01ledav002.gho.pok.ibm.com [9.57.199.107]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 0336MOeH15008554 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 3 Apr 2020 06:22:24 GMT Received: from b01ledav002.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6B2FC124052; Fri, 3 Apr 2020 06:22:24 +0000 (GMT) Received: from b01ledav002.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BD7E3124054; Fri, 3 Apr 2020 06:22:23 +0000 (GMT) Received: from sofia.ibm.com (unknown [9.199.34.1]) by b01ledav002.gho.pok.ibm.com (Postfix) with ESMTP; Fri, 3 Apr 2020 06:22:23 +0000 (GMT) Received: by sofia.ibm.com (Postfix, from userid 1000) id 0FFDA2E2F59; Fri, 3 Apr 2020 11:45:36 +0530 (IST) Date: Fri, 3 Apr 2020 11:45:36 +0530 From: Gautham R Shenoy To: "Naveen N. Rao" Cc: "Gautham R. Shenoy" , Kamalesh Babulal , Michael Ellerman , Nathan Lynch , Vaidyanathan Srinivasan , Tyrel Datwyler , linux-kernel@vger.kernel.org, linuxppc-dev@lists.ozlabs.org Subject: Re: [PATCH v4 2/6] powerpc/idle: Add accessor function to always read latest idle PURR Message-ID: <20200403061536.GA9066@in.ibm.com> Reply-To: ego@linux.vnet.ibm.com References: <1585308760-28792-1-git-send-email-ego@linux.vnet.ibm.com> <1585308760-28792-3-git-send-email-ego@linux.vnet.ibm.com> <1585734073.0qmf6bbdoa.naveen@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1585734073.0qmf6bbdoa.naveen@linux.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138,18.0.676 definitions=2020-04-03_03:2020-04-02,2020-04-03 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 mlxlogscore=999 impostorscore=0 phishscore=0 malwarescore=0 bulkscore=0 clxscore=1015 priorityscore=1501 mlxscore=0 suspectscore=0 spamscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004030046 Sender: linux-kernel-owner@vger.kernel.org Precedence: bulk List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On Wed, Apr 01, 2020 at 03:12:53PM +0530, Naveen N. Rao wrote: > Hi Gautham, > > Gautham R. Shenoy wrote: > >From: "Gautham R. Shenoy" > > > >Currently when CPU goes idle, we take a snapshot of PURR via > >pseries_idle_prolog() which is used at the CPU idle exit to compute > >the idle PURR cycles via the function pseries_idle_epilog(). Thus, > >the value of idle PURR cycle thus read before pseries_idle_prolog() and > >after pseries_idle_epilog() is always correct. > > > >However, if we were to read the idle PURR cycles from an interrupt > >context between pseries_idle_prolog() and pseries_idle_epilog() (this will > >be done in a future patch), then, the value of the idle PURR thus read > >will not include the cycles spent in the most recent idle period. > > > >This patch addresses the issue by providing accessor function to read > >the idle PURR such such that it includes the cycles spent in the most > >recent idle period, if we read it between pseries_idle_prolog() and > >pseries_idle_epilog(). In order to achieve it, the patch saves the > >snapshot of PURR in pseries_idle_prolog() in a per-cpu variable, > >instead of on the stack, so that it can be accessed from an interrupt > >context. > > > >Signed-off-by: Gautham R. Shenoy > >--- > > arch/powerpc/include/asm/idle.h | 47 +++++++++++++++++++++++++++------- > > arch/powerpc/platforms/pseries/setup.c | 7 +++-- > > drivers/cpuidle/cpuidle-pseries.c | 15 +++++------ > > 3 files changed, 47 insertions(+), 22 deletions(-) > > > >diff --git a/arch/powerpc/include/asm/idle.h b/arch/powerpc/include/asm/idle.h > >index 32064a4c..d4bfb6a 100644 > >--- a/arch/powerpc/include/asm/idle.h > >+++ b/arch/powerpc/include/asm/idle.h > >@@ -5,10 +5,27 @@ > > #include > > > > #ifdef CONFIG_PPC_PSERIES > >-static inline void pseries_idle_prolog(unsigned long *in_purr) > >+DECLARE_PER_CPU(u64, idle_entry_purr_snap); > >+ > >+static inline void snapshot_purr_idle_entry(void) > >+{ > >+ *this_cpu_ptr(&idle_entry_purr_snap) = mfspr(SPRN_PURR); > >+} > >+ > >+static inline void update_idle_purr_accounting(void) > >+{ > >+ u64 wait_cycles; > >+ u64 in_purr = *this_cpu_ptr(&idle_entry_purr_snap); > >+ > >+ wait_cycles = be64_to_cpu(get_lppaca()->wait_state_cycles); > >+ wait_cycles += mfspr(SPRN_PURR) - in_purr; > >+ get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles); > >+} > >+ > >+static inline void pseries_idle_prolog(void) > > { > > ppc64_runlatch_off(); > >- *in_purr = mfspr(SPRN_PURR); > >+ snapshot_purr_idle_entry(); > > /* > > * Indicate to the HV that we are idle. Now would be > > * a good time to find other work to dispatch. > >@@ -16,16 +33,28 @@ static inline void pseries_idle_prolog(unsigned long *in_purr) > > get_lppaca()->idle = 1; > > } > > > >-static inline void pseries_idle_epilog(unsigned long in_purr) > >+static inline void pseries_idle_epilog(void) > > { > >- u64 wait_cycles; > >- > >- wait_cycles = be64_to_cpu(get_lppaca()->wait_state_cycles); > >- wait_cycles += mfspr(SPRN_PURR) - in_purr; > >- get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles); > >+ update_idle_purr_accounting(); > > get_lppaca()->idle = 0; > >- > > ppc64_runlatch_on(); > > } > >+ > >+static inline u64 read_this_idle_purr(void) > >+{ > >+ /* > >+ * If we are reading from an idle context, update the > >+ * idle-purr cycles corresponding to the last idle period. > >+ * Since the idle context is not yet over, take a fresh > >+ * snapshot of the idle-purr. > >+ */ > >+ if (unlikely(get_lppaca()->idle == 1)) { > >+ update_idle_purr_accounting(); > >+ snapshot_purr_idle_entry(); > >+ } > >+ > >+ return be64_to_cpu(get_lppaca()->wait_state_cycles); > >+} > >+ > > I think this and read_this_idle_spurr() from the next patch should be moved > to Patch 4/6, where they are actually used. The reason I included this function in this patch was to justify why we were introducing snapshotting the purr values in a global per-cpu variable instead of on a stack variable. The reason being that someone might want to read the PURR value from an interrupt context which had woken up the CPU from idle. At this point, since epilog() function wasn't called, the idle PURR count corresponding to this latest idle period would have been accumulated in lppaca->wait_cycles. Thus, this helper function safely reads the value by 1) First updating the lppaca->wait_cycles with the latest idle_purr count. 2) Take a fresh snapshot, since the time from now to the epilog() call is also counted under idle CPU. So the PURR cycle increment during this short period should also be accumulated in lppaca->wait_cycles. prolog() | snapshot PURR | | | Idle | | <----- Interrupt . Read idle PURR ---- update idle PURR; | snapshot PURR; | Read idle PURR. | epilog() update idle PURR > > - Naveen > However, if you feel that moving this function to Patch 4 where it is actually used makes it more readable, I can do that. -- Thanks and Regards gautham. 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=-8.3 required=3.0 tests=HEADER_FROM_DIFFERENT_DOMAINS, INCLUDES_PATCH,MAILING_LIST_MULTI,SIGNED_OFF_BY,SPF_HELO_NONE,SPF_PASS, USER_AGENT_SANE_1 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 1C1C3C43331 for ; Fri, 3 Apr 2020 06:24:11 +0000 (UTC) Received: from lists.ozlabs.org (lists.ozlabs.org [203.11.71.2]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.kernel.org (Postfix) with ESMTPS id B76D820721 for ; Fri, 3 Apr 2020 06:24:10 +0000 (UTC) DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org B76D820721 Authentication-Results: mail.kernel.org; dmarc=fail (p=none dis=none) header.from=linux.vnet.ibm.com Authentication-Results: mail.kernel.org; spf=pass smtp.mailfrom=linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Received: from lists.ozlabs.org (lists.ozlabs.org [IPv6:2401:3900:2:1::3]) by lists.ozlabs.org (Postfix) with ESMTP id 48tqdh0VLqzDrgs for ; Fri, 3 Apr 2020 17:24:08 +1100 (AEDT) Authentication-Results: lists.ozlabs.org; spf=none (no SPF record) smtp.mailfrom=linux.vnet.ibm.com (client-ip=148.163.158.5; helo=mx0a-001b2d01.pphosted.com; envelope-from=ego@linux.vnet.ibm.com; receiver=) Authentication-Results: lists.ozlabs.org; dmarc=none (p=none dis=none) header.from=linux.vnet.ibm.com Received: from mx0a-001b2d01.pphosted.com (mx0b-001b2d01.pphosted.com [148.163.158.5]) (using TLSv1.2 with cipher ECDHE-RSA-AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by lists.ozlabs.org (Postfix) with ESMTPS id 48tqbr2CXYzDqYj for ; Fri, 3 Apr 2020 17:22:32 +1100 (AEDT) Received: from pps.filterd (m0098414.ppops.net [127.0.0.1]) by mx0b-001b2d01.pphosted.com (8.16.0.42/8.16.0.42) with SMTP id 0335dSnM087477; Fri, 3 Apr 2020 02:22:25 -0400 Received: from ppma03wdc.us.ibm.com (ba.79.3fa9.ip4.static.sl-reverse.com [169.63.121.186]) by mx0b-001b2d01.pphosted.com with ESMTP id 305s8309m9-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 03 Apr 2020 02:22:25 -0400 Received: from pps.filterd (ppma03wdc.us.ibm.com [127.0.0.1]) by ppma03wdc.us.ibm.com (8.16.0.27/8.16.0.27) with SMTP id 0336LfaW001775; Fri, 3 Apr 2020 06:22:24 GMT Received: from b01cxnp22036.gho.pok.ibm.com (b01cxnp22036.gho.pok.ibm.com [9.57.198.26]) by ppma03wdc.us.ibm.com with ESMTP id 301x776wcd-1 (version=TLSv1.2 cipher=ECDHE-RSA-AES256-GCM-SHA384 bits=256 verify=NOT); Fri, 03 Apr 2020 06:22:24 +0000 Received: from b01ledav002.gho.pok.ibm.com (b01ledav002.gho.pok.ibm.com [9.57.199.107]) by b01cxnp22036.gho.pok.ibm.com (8.14.9/8.14.9/NCO v10.0) with ESMTP id 0336MOeH15008554 (version=TLSv1/SSLv3 cipher=DHE-RSA-AES256-GCM-SHA384 bits=256 verify=OK); Fri, 3 Apr 2020 06:22:24 GMT Received: from b01ledav002.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id 6B2FC124052; Fri, 3 Apr 2020 06:22:24 +0000 (GMT) Received: from b01ledav002.gho.pok.ibm.com (unknown [127.0.0.1]) by IMSVA (Postfix) with ESMTP id BD7E3124054; Fri, 3 Apr 2020 06:22:23 +0000 (GMT) Received: from sofia.ibm.com (unknown [9.199.34.1]) by b01ledav002.gho.pok.ibm.com (Postfix) with ESMTP; Fri, 3 Apr 2020 06:22:23 +0000 (GMT) Received: by sofia.ibm.com (Postfix, from userid 1000) id 0FFDA2E2F59; Fri, 3 Apr 2020 11:45:36 +0530 (IST) Date: Fri, 3 Apr 2020 11:45:36 +0530 From: Gautham R Shenoy To: "Naveen N. Rao" Subject: Re: [PATCH v4 2/6] powerpc/idle: Add accessor function to always read latest idle PURR Message-ID: <20200403061536.GA9066@in.ibm.com> References: <1585308760-28792-1-git-send-email-ego@linux.vnet.ibm.com> <1585308760-28792-3-git-send-email-ego@linux.vnet.ibm.com> <1585734073.0qmf6bbdoa.naveen@linux.ibm.com> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1585734073.0qmf6bbdoa.naveen@linux.ibm.com> User-Agent: Mutt/1.5.23 (2014-03-12) X-TM-AS-GCONF: 00 X-Proofpoint-Virus-Version: vendor=fsecure engine=2.50.10434:6.0.138, 18.0.676 definitions=2020-04-03_03:2020-04-02, 2020-04-03 signatures=0 X-Proofpoint-Spam-Details: rule=outbound_notspam policy=outbound score=0 lowpriorityscore=0 mlxlogscore=999 impostorscore=0 phishscore=0 malwarescore=0 bulkscore=0 clxscore=1015 priorityscore=1501 mlxscore=0 suspectscore=0 spamscore=0 adultscore=0 classifier=spam adjust=0 reason=mlx scancount=1 engine=8.12.0-2003020000 definitions=main-2004030046 X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Reply-To: ego@linux.vnet.ibm.com Cc: Nathan Lynch , "Gautham R. Shenoy" , Tyrel Datwyler , linux-kernel@vger.kernel.org, Kamalesh Babulal , Vaidyanathan Srinivasan , linuxppc-dev@lists.ozlabs.org Errors-To: linuxppc-dev-bounces+linuxppc-dev=archiver.kernel.org@lists.ozlabs.org Sender: "Linuxppc-dev" On Wed, Apr 01, 2020 at 03:12:53PM +0530, Naveen N. Rao wrote: > Hi Gautham, > > Gautham R. Shenoy wrote: > >From: "Gautham R. Shenoy" > > > >Currently when CPU goes idle, we take a snapshot of PURR via > >pseries_idle_prolog() which is used at the CPU idle exit to compute > >the idle PURR cycles via the function pseries_idle_epilog(). Thus, > >the value of idle PURR cycle thus read before pseries_idle_prolog() and > >after pseries_idle_epilog() is always correct. > > > >However, if we were to read the idle PURR cycles from an interrupt > >context between pseries_idle_prolog() and pseries_idle_epilog() (this will > >be done in a future patch), then, the value of the idle PURR thus read > >will not include the cycles spent in the most recent idle period. > > > >This patch addresses the issue by providing accessor function to read > >the idle PURR such such that it includes the cycles spent in the most > >recent idle period, if we read it between pseries_idle_prolog() and > >pseries_idle_epilog(). In order to achieve it, the patch saves the > >snapshot of PURR in pseries_idle_prolog() in a per-cpu variable, > >instead of on the stack, so that it can be accessed from an interrupt > >context. > > > >Signed-off-by: Gautham R. Shenoy > >--- > > arch/powerpc/include/asm/idle.h | 47 +++++++++++++++++++++++++++------- > > arch/powerpc/platforms/pseries/setup.c | 7 +++-- > > drivers/cpuidle/cpuidle-pseries.c | 15 +++++------ > > 3 files changed, 47 insertions(+), 22 deletions(-) > > > >diff --git a/arch/powerpc/include/asm/idle.h b/arch/powerpc/include/asm/idle.h > >index 32064a4c..d4bfb6a 100644 > >--- a/arch/powerpc/include/asm/idle.h > >+++ b/arch/powerpc/include/asm/idle.h > >@@ -5,10 +5,27 @@ > > #include > > > > #ifdef CONFIG_PPC_PSERIES > >-static inline void pseries_idle_prolog(unsigned long *in_purr) > >+DECLARE_PER_CPU(u64, idle_entry_purr_snap); > >+ > >+static inline void snapshot_purr_idle_entry(void) > >+{ > >+ *this_cpu_ptr(&idle_entry_purr_snap) = mfspr(SPRN_PURR); > >+} > >+ > >+static inline void update_idle_purr_accounting(void) > >+{ > >+ u64 wait_cycles; > >+ u64 in_purr = *this_cpu_ptr(&idle_entry_purr_snap); > >+ > >+ wait_cycles = be64_to_cpu(get_lppaca()->wait_state_cycles); > >+ wait_cycles += mfspr(SPRN_PURR) - in_purr; > >+ get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles); > >+} > >+ > >+static inline void pseries_idle_prolog(void) > > { > > ppc64_runlatch_off(); > >- *in_purr = mfspr(SPRN_PURR); > >+ snapshot_purr_idle_entry(); > > /* > > * Indicate to the HV that we are idle. Now would be > > * a good time to find other work to dispatch. > >@@ -16,16 +33,28 @@ static inline void pseries_idle_prolog(unsigned long *in_purr) > > get_lppaca()->idle = 1; > > } > > > >-static inline void pseries_idle_epilog(unsigned long in_purr) > >+static inline void pseries_idle_epilog(void) > > { > >- u64 wait_cycles; > >- > >- wait_cycles = be64_to_cpu(get_lppaca()->wait_state_cycles); > >- wait_cycles += mfspr(SPRN_PURR) - in_purr; > >- get_lppaca()->wait_state_cycles = cpu_to_be64(wait_cycles); > >+ update_idle_purr_accounting(); > > get_lppaca()->idle = 0; > >- > > ppc64_runlatch_on(); > > } > >+ > >+static inline u64 read_this_idle_purr(void) > >+{ > >+ /* > >+ * If we are reading from an idle context, update the > >+ * idle-purr cycles corresponding to the last idle period. > >+ * Since the idle context is not yet over, take a fresh > >+ * snapshot of the idle-purr. > >+ */ > >+ if (unlikely(get_lppaca()->idle == 1)) { > >+ update_idle_purr_accounting(); > >+ snapshot_purr_idle_entry(); > >+ } > >+ > >+ return be64_to_cpu(get_lppaca()->wait_state_cycles); > >+} > >+ > > I think this and read_this_idle_spurr() from the next patch should be moved > to Patch 4/6, where they are actually used. The reason I included this function in this patch was to justify why we were introducing snapshotting the purr values in a global per-cpu variable instead of on a stack variable. The reason being that someone might want to read the PURR value from an interrupt context which had woken up the CPU from idle. At this point, since epilog() function wasn't called, the idle PURR count corresponding to this latest idle period would have been accumulated in lppaca->wait_cycles. Thus, this helper function safely reads the value by 1) First updating the lppaca->wait_cycles with the latest idle_purr count. 2) Take a fresh snapshot, since the time from now to the epilog() call is also counted under idle CPU. So the PURR cycle increment during this short period should also be accumulated in lppaca->wait_cycles. prolog() | snapshot PURR | | | Idle | | <----- Interrupt . Read idle PURR ---- update idle PURR; | snapshot PURR; | Read idle PURR. | epilog() update idle PURR > > - Naveen > However, if you feel that moving this function to Patch 4 where it is actually used makes it more readable, I can do that. -- Thanks and Regards gautham.