From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1752427AbbJWCT4 (ORCPT ); Thu, 22 Oct 2015 22:19:56 -0400 Received: from mail-pa0-f47.google.com ([209.85.220.47]:33118 "EHLO mail-pa0-f47.google.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1751228AbbJWCTz (ORCPT ); Thu, 22 Oct 2015 22:19:55 -0400 Date: Fri, 23 Oct 2015 07:49:51 +0530 From: Viresh Kumar To: Yunhong Jiang Cc: Frederic Weisbecker , Thomas Gleixner , linux-kernel@vger.kernel.org Subject: Re: [PATCH] timer: Lazily wakup nohz CPU when adding new timer. Message-ID: <20151023021951.GP3897@ubuntu> References: <1443466096-31252-1-git-send-email-yunhong.jiang@linux.intel.com> <20151020224751.GB31289@jnakajim-build> <20151021104631.GB7784@ubuntu> <20151022214003.GA22993@jnakajim-build> MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <20151022214003.GA22993@jnakajim-build> User-Agent: Mutt/1.5.21 (2010-09-15) Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 22-10-15, 14:40, Yunhong Jiang wrote: > A naive question is, why it's sure a tick will happen when the tickless > processor is in idle? How do you get this impression? I don't think anyone has said that. We are talking about deferrable timers, which by design are only required if the target CPU is not-idle. If it is idle, then the timer isn't required to be serviced until the CPU wakes up. And the CPU can take whatever time it wants to wake up again. > Is it because scheduler load balance is sure to send a > tick to the processor in future? No. We aren't expecting the CPU to wake up any time soon. Just ignore the deferrable timer. -- viresh