From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S932674AbeEWLdc (ORCPT ); Wed, 23 May 2018 07:33:32 -0400 Received: from mx3-rdu2.redhat.com ([66.187.233.73]:53580 "EHLO mx1.redhat.com" rhost-flags-OK-OK-OK-FAIL) by vger.kernel.org with ESMTP id S932529AbeEWLdb (ORCPT ); Wed, 23 May 2018 07:33:31 -0400 From: Miroslav Lichvar To: linux-kernel@vger.kernel.org Cc: Miroslav Lichvar , Thomas Gleixner , John Stultz , Richard Cochran , Prarit Bhargava Subject: [PATCH RFC] timekeeping: Update multiplier when NTP frequency is set directly Date: Wed, 23 May 2018 13:33:21 +0200 Message-Id: <20180523113321.20404-1-mlichvar@redhat.com> Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org When the NTP frequency is set directly from userspace using the ADJ_FREQUENCY or ADJ_TICK timex mode, immediately update the timekeeper's multiplier instead of waiting for the next tick. This removes a hidden non-deterministic delay in setting of the frequency and allows an extremely tight control of the system clock with update rates close to or even exceeding the kernel HZ. Cc: Thomas Gleixner Cc: John Stultz Cc: Richard Cochran Cc: Prarit Bhargava Signed-off-by: Miroslav Lichvar --- kernel/time/timekeeping.c | 8 ++++---- 1 file changed, 4 insertions(+), 4 deletions(-) diff --git a/kernel/time/timekeeping.c b/kernel/time/timekeeping.c index 49cbceef5deb..6922dae7317c 100644 --- a/kernel/time/timekeeping.c +++ b/kernel/time/timekeeping.c @@ -2047,10 +2047,6 @@ void update_wall_time(void) tk->tkr_mono.cycle_last, tk->tkr_mono.mask); #endif - /* Check if there's really nothing to do */ - if (offset < real_tk->cycle_interval) - goto out; - /* Do some additional sanity checking */ timekeeping_check_update(tk, offset); @@ -2332,6 +2328,10 @@ int do_adjtimex(struct timex *txc) write_seqcount_end(&tk_core.seq); raw_spin_unlock_irqrestore(&timekeeper_lock, flags); + /* Update the multiplier immediately if frequency was set directly */ + if (txc->modes & (ADJ_FREQUENCY | ADJ_TICK)) + update_wall_time(); + if (tai != orig_tai) clock_was_set(); -- 2.14.3