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=-6.8 required=3.0 tests=DKIMWL_WL_HIGH,DKIM_SIGNED, DKIM_VALID,HEADER_FROM_DIFFERENT_DOMAINS,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 F013BC48BD4 for ; Tue, 25 Jun 2019 17:03:21 +0000 (UTC) Received: from bombadil.infradead.org (bombadil.infradead.org [198.137.202.133]) (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 A478220883 for ; Tue, 25 Jun 2019 17:03:21 +0000 (UTC) Authentication-Results: mail.kernel.org; dkim=pass (2048-bit key) header.d=lists.infradead.org header.i=@lists.infradead.org header.b="mjChTLG1" DMARC-Filter: OpenDMARC Filter v1.3.2 mail.kernel.org A478220883 Authentication-Results: mail.kernel.org; dmarc=none (p=none dis=none) header.from=linutronix.de Authentication-Results: mail.kernel.org; spf=none smtp.mailfrom=linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org 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:Cc:List-Subscribe:List-Help:List-Post: List-Archive:List-Unsubscribe:List-Id:MIME-Version:References:Message-ID: In-Reply-To:Subject:To:From:Date:Reply-To:Content-ID:Content-Description: Resent-Date:Resent-From:Resent-Sender:Resent-To:Resent-Cc:Resent-Message-ID: List-Owner; bh=Ny4AYbjLTG2rMzoyWu25+znbncXdIfyBjJZhLF8iVKc=; b=mjChTLG1vaCy50 ztYaBGufoIliadp2IS1l/+4IytM7ILEi1agbU0WqY0RIpfQTMwxcFCZV+TbooxQgn5/mpyVeQJO0a hxPqom0lxDDJZkqfk3BSu2CkLZk+0mR90zv/rWTD4Y3BdF0cCv+XLEoxmUIDxRzbrIZhbuCvV7Kkt SM/NqWLrTSPto/oMOrd6q5/c2SEZ/4tkx4/ewJZGaQC80/fHa1OZP5EY5QUfgcg+C1cWz9KTtmrnO n6DR28eRQeTC36gOhvwPWBv+wpgE75QTb2Iiz+feKwb7OrUYujiBuEuy/pjHejHFHwPkkK0q8xNAa ZIdYS99ogZb7qDspX+wA==; Received: from localhost ([127.0.0.1] helo=bombadil.infradead.org) by bombadil.infradead.org with esmtp (Exim 4.92 #3 (Red Hat Linux)) id 1hfoqj-0004eU-T2; Tue, 25 Jun 2019 17:03:18 +0000 Received: from galois.linutronix.de ([2a0a:51c0:0:12e:550::1]) by bombadil.infradead.org with esmtps (Exim 4.92 #3 (Red Hat Linux)) id 1hfopo-00046d-Ks for linux-arm-kernel@lists.infradead.org; Tue, 25 Jun 2019 17:02:23 +0000 Received: from p5b06daab.dip0.t-ipconnect.de ([91.6.218.171] helo=nanos) by Galois.linutronix.de with esmtpsa (TLS1.2:DHE_RSA_AES_256_CBC_SHA256:256) (Exim 4.80) (envelope-from ) id 1hfopi-0004Hb-GJ; Tue, 25 Jun 2019 19:02:14 +0200 Date: Tue, 25 Jun 2019 19:02:13 +0200 (CEST) From: Thomas Gleixner To: Vincenzo Frascino Subject: Re: [PATCH 1/3] lib/vdso: Delay mask application in do_hres() In-Reply-To: <20190625161804.38713-1-vincenzo.frascino@arm.com> Message-ID: References: <20190624133607.GI29497@fuggles.cambridge.arm.com> <20190625161804.38713-1-vincenzo.frascino@arm.com> User-Agent: Alpine 2.21 (DEB 202 2017-01-01) MIME-Version: 1.0 X-Linutronix-Spam-Score: -1.0 X-Linutronix-Spam-Level: - X-Linutronix-Spam-Status: No , -1.0 points, 5.0 required, ALL_TRUSTED=-1, SHORTCIRCUIT=-0.0001 X-CRM114-Version: 20100106-BlameMichelson ( TRE 0.8.0 (BSD) ) MR-646709E3 X-CRM114-CacheID: sfid-20190625_100221_589953_2B5FA1DB X-CRM114-Status: GOOD ( 20.30 ) X-BeenThere: linux-arm-kernel@lists.infradead.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , Cc: linux-arch@vger.kernel.org, shuah@kernel.org, sthotton@marvell.com, andre.przywara@arm.com, Arnd Bergmann , huw@codeweavers.com, catalin.marinas@arm.com, Daniel Lezcano , Will Deacon , LKML , Ralf Baechle , linux-mips@vger.kernel.org, Andy Lutomirski , paul.burton@mips.com, linux-kselftest@vger.kernel.org, linux@rasmusvillemoes.dk, linux@armlinux.org.uk, 0x7f454c46@gmail.com, salyzyn@android.com, pcc@google.com, LAK Content-Type: text/plain; charset="us-ascii" Content-Transfer-Encoding: 7bit Sender: "linux-arm-kernel" Errors-To: linux-arm-kernel-bounces+infradead-linux-arm-kernel=archiver.kernel.org@lists.infradead.org On Tue, 25 Jun 2019, Vincenzo Frascino wrote: CC+ Andy > do_hres() in the vDSO generic library masks the hw counter value > immediately after reading it. > > Postpone the mask application after checking if the syscall fallback is > enabled, in order to be able to detect a possible fallback for the > architectures that have masks smaller than ULLONG_MAX. Right. This only worked on x86 because the mask is there ULLONG_MAX for all VDSO capable clocksources, i.e. that ever worked just by chance. As we talked about that already yesterday, I tested this on a couple of machines and as expected the outcome is uarch dependent. Minimal deviations to both sides and some machines do not show any change at all. I doubt it's possible to come up with a solution which makes all uarchs go faster magically. Though, thinking about it, we could remove the mask operation completely on X86. /me runs tests Thanks, tglx > Signed-off-by: Vincenzo Frascino > --- > lib/vdso/gettimeofday.c | 4 ++-- > 1 file changed, 2 insertions(+), 2 deletions(-) > > diff --git a/lib/vdso/gettimeofday.c b/lib/vdso/gettimeofday.c > index ef28cc5d7bff..ee1221ba1d32 100644 > --- a/lib/vdso/gettimeofday.c > +++ b/lib/vdso/gettimeofday.c > @@ -35,12 +35,12 @@ static int do_hres(const struct vdso_data *vd, clockid_t clk, > > do { > seq = vdso_read_begin(vd); > - cycles = __arch_get_hw_counter(vd->clock_mode) & > - vd->mask; > + cycles = __arch_get_hw_counter(vd->clock_mode); > ns = vdso_ts->nsec; > last = vd->cycle_last; > if (unlikely((s64)cycles < 0)) > return clock_gettime_fallback(clk, ts); > + cycles &= vd->mask; > if (cycles > last) > ns += (cycles - last) * vd->mult; > ns >>= vd->shift; > -- > 2.22.0 > > _______________________________________________ linux-arm-kernel mailing list linux-arm-kernel@lists.infradead.org http://lists.infradead.org/mailman/listinfo/linux-arm-kernel