From patchwork Fri Oct 13 13:32:56 2017 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Julien Thierry X-Patchwork-Id: 10004777 Return-Path: Received: from mail.wl.linuxfoundation.org (pdx-wl-mail.web.codeaurora.org [172.30.200.125]) by pdx-korg-patchwork.web.codeaurora.org (Postfix) with ESMTP id D412D60360 for ; Fri, 13 Oct 2017 13:51:51 +0000 (UTC) Received: from mail.wl.linuxfoundation.org (localhost [127.0.0.1]) by mail.wl.linuxfoundation.org (Postfix) with ESMTP id C55FE29060 for ; Fri, 13 Oct 2017 13:51:51 +0000 (UTC) Received: by mail.wl.linuxfoundation.org (Postfix, from userid 486) id BA0A72907F; Fri, 13 Oct 2017 13:51:51 +0000 (UTC) X-Spam-Checker-Version: SpamAssassin 3.3.1 (2010-03-16) on pdx-wl-mail.web.codeaurora.org X-Spam-Level: X-Spam-Status: No, score=-4.2 required=2.0 tests=BAYES_00,DKIM_SIGNED, DKIM_VALID,RCVD_IN_DNSWL_MED autolearn=ham version=3.3.1 Received: from bombadil.infradead.org (bombadil.infradead.org [65.50.211.133]) (using TLSv1.2 with cipher AES256-GCM-SHA384 (256/256 bits)) (No client certificate requested) by mail.wl.linuxfoundation.org (Postfix) with ESMTPS id 1E3F329079 for ; Fri, 13 Oct 2017 13:51:50 +0000 (UTC) DKIM-Signature: v=1; a=rsa-sha256; q=dns/txt; c=relaxed/relaxed; d=lists.infradead.org; s=bombadil.20170209; h=Sender: Content-Transfer-Encoding:Content-Type:MIME-Version:Cc:List-Subscribe: List-Help:List-Post:List-Archive:List-Unsubscribe:List-Id:References: In-Reply-To:Message-Id:Date:Subject:To:From:Reply-To:Content-ID: Content-Description:Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc :Resent-Message-ID:List-Owner; bh=8w4t+3WKoBXml3eRlwsiWDkNrcpGbtl9/xs6yLRdPVo=; b=jCOid/7pEs4ivVh3ucdKWD7KYk Li0m6E7OuQnpfvhb73IkkN/WAY8vSNUsUsmkKBWeDrtIANPylB4PgZmaNbpwXFuqNYZ8yO0e/kv9c FMkrqmEGPZZvDEAnZSm43hjkilCWTw21SHgGfr80zSPxRF10+rOZlneU4LylGzS4ZALIcwVyYrTFI GYE28DHDUPAZdRVu7rj8pOPFyFofGtNMTunNyBYB+9T+Zfe0C4WWVZc4VxgkHtSbGtyis32V+Hl38 5pAXr5y3cEdHIfT2Oyu+YYJCHe2cABz4w6X/YDXYEyUWekVo4PmspWVC7P3a2ssIoE8Tc9PXW2BMn SDUGbJvQ==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1e30NQ-0008DM-W0; Fri, 13 Oct 2017 13:51:49 +0000 Received: from usa-sjc-mx-foss1.foss.arm.com ([217.140.101.70] helo=foss.arm.com) by bombadil.infradead.org with esmtp (Exim 4.87 #1 (Red Hat Linux)) id 1e305c-0004m5-56 for linux-arm-kernel@lists.infradead.org; Fri, 13 Oct 2017 13:33:29 +0000 Received: from usa-sjc-imap-foss1.foss.arm.com (unknown [10.72.51.249]) by usa-sjc-mx-foss1.foss.arm.com (Postfix) with ESMTP id 94195164F; Fri, 13 Oct 2017 06:33:08 -0700 (PDT) Received: from e112298-lin.cambridge.arm.com (usa-sjc-imap-foss1.foss.arm.com [10.72.51.249]) by usa-sjc-imap-foss1.foss.arm.com (Postfix) with ESMTPA id 79FDC3F3E1; Fri, 13 Oct 2017 06:33:07 -0700 (PDT) From: Julien Thierry To: linux-arm-kernel@lists.infradead.org Subject: [PATCH v4 2/2] arm64: use WFE for long delays Date: Fri, 13 Oct 2017 14:32:56 +0100 Message-Id: <1507901576-34641-3-git-send-email-julien.thierry@arm.com> X-Mailer: git-send-email 1.9.1 In-Reply-To: <1507901576-34641-1-git-send-email-julien.thierry@arm.com> References: <1507901576-34641-1-git-send-email-julien.thierry@arm.com> X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20171013_063324_300641_1A545009 X-CRM114-Status: GOOD ( 12.53 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.21 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: mark.rutland@arm.com, Catalin Marinas , will.deacon@arm.com, Julien Thierry MIME-Version: 1.0 Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+patchwork-linux-arm=patchwork.kernel.org@lists.infradead.org X-Virus-Scanned: ClamAV using ClamSMTP The current delay implementation uses the yield instruction, which is a hint that it is beneficial to schedule another thread. As this is a hint, it may be implemented as a NOP, causing all delays to be busy loops. This is the case for many existing CPUs. Taking advantage of the generic timer sending periodic events to all cores, we can use WFE during delays to reduce power consumption. This is beneficial only for delays longer than the period of the timer event stream. If timer event stream is not enabled, delays will behave as yield/busy loops. Signed-off-by: Julien Thierry Cc: Catalin Marinas Cc: Will Deacon Cc: Mark Rutland --- arch/arm64/lib/delay.c | 23 +++++++++++++++++++---- include/clocksource/arm_arch_timer.h | 4 +++- 2 files changed, 22 insertions(+), 5 deletions(-) -- 1.9.1 diff --git a/arch/arm64/lib/delay.c b/arch/arm64/lib/delay.c index dad4ec9..e48ac40 100644 --- a/arch/arm64/lib/delay.c +++ b/arch/arm64/lib/delay.c @@ -24,10 +24,28 @@ #include #include +#include + +#define USECS_TO_CYCLES(time_usecs) \ + xloops_to_cycles((time_usecs) * 0x10C7UL) + +static inline unsigned long xloops_to_cycles(unsigned long xloops) +{ + return (xloops * loops_per_jiffy * HZ) >> 32; +} + void __delay(unsigned long cycles) { cycles_t start = get_cycles(); + if (arch_timer_evtstrm_available()) { + const cycles_t timer_evt_period = + USECS_TO_CYCLES(ARCH_TIMER_EVT_STREAM_PERIOD_US); + + while ((get_cycles() - start + timer_evt_period) < cycles) + wfe(); + } + while ((get_cycles() - start) < cycles) cpu_relax(); } @@ -35,10 +53,7 @@ void __delay(unsigned long cycles) inline void __const_udelay(unsigned long xloops) { - unsigned long loops; - - loops = xloops * loops_per_jiffy * HZ; - __delay(loops >> 32); + __delay(xloops_to_cycles(xloops)); } EXPORT_SYMBOL(__const_udelay); diff --git a/include/clocksource/arm_arch_timer.h b/include/clocksource/arm_arch_timer.h index 4e28283..349e595 100644 --- a/include/clocksource/arm_arch_timer.h +++ b/include/clocksource/arm_arch_timer.h @@ -67,7 +67,9 @@ enum arch_timer_spi_nr { #define ARCH_TIMER_USR_VT_ACCESS_EN (1 << 8) /* virtual timer registers */ #define ARCH_TIMER_USR_PT_ACCESS_EN (1 << 9) /* physical timer registers */ -#define ARCH_TIMER_EVT_STREAM_FREQ 10000 /* 100us */ +#define ARCH_TIMER_EVT_STREAM_PERIOD_US 100 +#define ARCH_TIMER_EVT_STREAM_FREQ \ + (USEC_PER_SEC / ARCH_TIMER_EVT_STREAM_PERIOD_US) struct arch_timer_kvm_info { struct timecounter timecounter;