From patchwork Wed Apr 18 16:01:19 2012 Content-Type: text/plain; charset="utf-8" MIME-Version: 1.0 Content-Transfer-Encoding: 7bit X-Patchwork-Submitter: Bharat Bhushan X-Patchwork-Id: 153537 Return-Path: X-Original-To: patchwork-incoming@ozlabs.org Delivered-To: patchwork-incoming@ozlabs.org Received: from ozlabs.org (localhost [IPv6:::1]) by ozlabs.org (Postfix) with ESMTP id 74E09B70C8 for ; Thu, 19 Apr 2012 01:49:39 +1000 (EST) Received: from am1outboundpool.messaging.microsoft.com (am1ehsobe003.messaging.microsoft.com [213.199.154.206]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "mail.global.frontbridge.com", Issuer "Microsoft Secure Server Authority" (not verified)) by ozlabs.org (Postfix) with ESMTPS id CD25AB6EEC for ; Thu, 19 Apr 2012 01:48:51 +1000 (EST) Received: from mail29-am1-R.bigfish.com (10.3.201.245) by AM1EHSOBE004.bigfish.com (10.3.204.24) with Microsoft SMTP Server id 14.1.225.23; Wed, 18 Apr 2012 15:48:45 +0000 Received: from mail29-am1 (localhost [127.0.0.1]) by mail29-am1-R.bigfish.com (Postfix) with ESMTP id 21E2D180291; Wed, 18 Apr 2012 15:48:45 +0000 (UTC) X-SpamScore: 3 X-BigFish: VS3(zzzz1202h1082kzz8275bhz2dh2a8h668h839hd24h) X-Forefront-Antispam-Report: CIP:70.37.183.190; KIP:(null); UIP:(null); IPV:NLI; H:mail.freescale.net; RD:none; EFVD:NLI Received: from mail29-am1 (localhost.localdomain [127.0.0.1]) by mail29-am1 (MessageSwitch) id 1334764123306783_24542; Wed, 18 Apr 2012 15:48:43 +0000 (UTC) Received: from AM1EHSMHS009.bigfish.com (unknown [10.3.201.251]) by mail29-am1.bigfish.com (Postfix) with ESMTP id 3C82F2C0043; Wed, 18 Apr 2012 15:48:43 +0000 (UTC) Received: from mail.freescale.net (70.37.183.190) by AM1EHSMHS009.bigfish.com (10.3.207.109) with Microsoft SMTP Server (TLS) id 14.1.225.23; Wed, 18 Apr 2012 15:48:42 +0000 Received: from tx30smr01.am.freescale.net (10.81.153.31) by 039-SN1MMR1-002.039d.mgd.msft.net (10.84.1.15) with Microsoft SMTP Server (TLS) id 14.1.355.3; Wed, 18 Apr 2012 10:48:40 -0500 Received: from freescale.com ([10.232.15.72]) by tx30smr01.am.freescale.net (8.14.3/8.14.0) with SMTP id q3IFmXEI025996; Wed, 18 Apr 2012 08:48:34 -0700 Received: by freescale.com (sSMTP sendmail emulation); Wed, 18 Apr 2012 21:31:20 +0530 From: Bharat Bhushan To: , , , , Subject: [PATCH v4] KVM: PPC Use clockevent multiplier and shifter for decrementer Date: Wed, 18 Apr 2012 21:31:19 +0530 Message-ID: <1334764879-18020-1-git-send-email-bharat.bhushan@freescale.com> X-Mailer: git-send-email 1.7.0.4 MIME-Version: 1.0 X-OriginatorOrg: freescale.com Cc: Bharat Bhushan X-BeenThere: linuxppc-dev@lists.ozlabs.org X-Mailman-Version: 2.1.14 Precedence: list List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Errors-To: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Sender: linuxppc-dev-bounces+patchwork-incoming=ozlabs.org@lists.ozlabs.org Time for which the hrtimer is started for decrementer emulation is calculated using tb_ticks_per_usec. While hrtimer uses the clockevent for DEC reprogramming (if needed) and which calculate timebase ticks using the multiplier and shifter mechanism implemented within clockevent layer. It was observed that this conversion (timebase->time->timebase) are not correct because the mechanism are not consistent. In our setup it adds 2% jitter. With this patch clockevent multiplier and shifter mechanism are used when starting hrtimer for decrementer emulation. Now the jitter is < 0.5%. Signed-off-by: Bharat Bhushan --- v4: - Added comment in emulate.c arch/powerpc/include/asm/time.h | 1 + arch/powerpc/kernel/time.c | 3 ++- arch/powerpc/kvm/emulate.c | 9 +++++++-- 3 files changed, 10 insertions(+), 3 deletions(-) diff --git a/arch/powerpc/include/asm/time.h b/arch/powerpc/include/asm/time.h index 7eb10fb..b3c7959 100644 --- a/arch/powerpc/include/asm/time.h +++ b/arch/powerpc/include/asm/time.h @@ -28,6 +28,7 @@ extern unsigned long tb_ticks_per_jiffy; extern unsigned long tb_ticks_per_usec; extern unsigned long tb_ticks_per_sec; +extern struct clock_event_device decrementer_clockevent; struct rtc_time; extern void to_tm(int tim, struct rtc_time * tm); diff --git a/arch/powerpc/kernel/time.c b/arch/powerpc/kernel/time.c index 567dd7c..4f7a285 100644 --- a/arch/powerpc/kernel/time.c +++ b/arch/powerpc/kernel/time.c @@ -105,7 +105,7 @@ static int decrementer_set_next_event(unsigned long evt, static void decrementer_set_mode(enum clock_event_mode mode, struct clock_event_device *dev); -static struct clock_event_device decrementer_clockevent = { +struct clock_event_device decrementer_clockevent = { .name = "decrementer", .rating = 200, .irq = 0, @@ -113,6 +113,7 @@ static struct clock_event_device decrementer_clockevent = { .set_mode = decrementer_set_mode, .features = CLOCK_EVT_FEAT_ONESHOT, }; +EXPORT_SYMBOL(decrementer_clockevent); DEFINE_PER_CPU(u64, decrementers_next_tb); static DEFINE_PER_CPU(struct clock_event_device, decrementers); diff --git a/arch/powerpc/kvm/emulate.c b/arch/powerpc/kvm/emulate.c index afc9154..550a058 100644 --- a/arch/powerpc/kvm/emulate.c +++ b/arch/powerpc/kvm/emulate.c @@ -23,6 +23,7 @@ #include #include #include +#include #include #include @@ -104,8 +105,12 @@ void kvmppc_emulate_dec(struct kvm_vcpu *vcpu) */ dec_time = vcpu->arch.dec; - dec_time *= 1000; - do_div(dec_time, tb_ticks_per_usec); + /* + * Guest timebase ticks at the same frequency as host decrementer. + * So use the host decrementer calculations for decrementer emulation. + */ + dec_time = dec_time << decrementer_clockevent.shift; + do_div(dec_time, decrementer_clockevent.mult); dec_nsec = do_div(dec_time, NSEC_PER_SEC); hrtimer_start(&vcpu->arch.dec_timer, ktime_set(dec_time, dec_nsec), HRTIMER_MODE_REL);