From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751157AbdEaAkp (ORCPT ); Tue, 30 May 2017 20:40:45 -0400 Received: from camailhost.cavium.com ([12.108.191.230]:56034 "EHLO camailhost.cavium.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751002AbdEaAkn (ORCPT ); Tue, 30 May 2017 20:40:43 -0400 X-Greylist: delayed 351 seconds by postgrey-1.27 at vger.kernel.org; Tue, 30 May 2017 20:40:43 EDT From: Andrew Pinski To: linux-arm-kernel@lists.infradead.org, linux-kernel@vger.kernel.org Cc: Andrew Pinski Subject: [PATCH 2/2] arm64:vdso: Remove ISB from gettimeofday. Date: Tue, 30 May 2017 17:34:20 -0700 Message-Id: <1496190860-5116-2-git-send-email-apinski@cavium.com> X-Mailer: git-send-email 2.7.4 In-Reply-To: <1496190860-5116-1-git-send-email-apinski@cavium.com> References: <1496190860-5116-1-git-send-email-apinski@cavium.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org ISB is normally required before mrs CNTVCT if we want the mrs to completed after the loads. In this case it is not. As we are taking the difference and if that difference was going to be negative, we just use the last counter value instead. Signed-off-by: Andrew Pinski --- arch/arm64/kernel/vdso/gettimeofday.c | 14 ++++++++++++-- 1 file changed, 12 insertions(+), 2 deletions(-) diff --git a/arch/arm64/kernel/vdso/gettimeofday.c b/arch/arm64/kernel/vdso/gettimeofday.c index 1293786..49edd35 100644 --- a/arch/arm64/kernel/vdso/gettimeofday.c +++ b/arch/arm64/kernel/vdso/gettimeofday.c @@ -117,10 +117,20 @@ static notrace u64 get_clock_shifted_nsec(u64 cycle_last, u64 mult) u64 res; /* Read the virtual counter. */ - isb(); + /* + * This normally requires an ISB but since we know the + * read of the last cycle will always be after the + * read of the values are valid word. + */ asm volatile("mrs %0, cntvct_el0" : "=r" (res) :: "memory"); - res = res - cycle_last; + /* + * If the current cycle is greater than the last, + * then get the difference. + */ + if (res > cycle_last) + res = res - cycle_last; + /* We can only guarantee 56 bits of precision. */ res &= ~(0xff00ull<<48); return res * mult; -- 2.7.4