From mboxrd@z Thu Jan  1 00:00:00 1970
Return-Path: <linux-kernel-owner@vger.kernel.org>
Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand
	id S1752617AbcGMNwe (ORCPT <rfc822;w@1wt.eu>);
	Wed, 13 Jul 2016 09:52:34 -0400
Received: from mx1.redhat.com ([209.132.183.28]:34038 "EHLO mx1.redhat.com"
	rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP
	id S1751426AbcGMNw0 (ORCPT <rfc822;linux-kernel@vger.kernel.org>);
	Wed, 13 Jul 2016 09:52:26 -0400
Subject: Re: [PATCH v3 1/3] arch, x86, tsc deadline clockevent dev: reduce
 frequency roundoff error
To: Peter Zijlstra <peterz@infradead.org>,
        Nicolai Stange <nicstange@gmail.com>
References: <20160713130344.8319-1-nicstange@gmail.com>
 <20160713130344.8319-2-nicstange@gmail.com>
 <20160713134900.GU30154@twins.programming.kicks-ass.net>
Cc: Thomas Gleixner <tglx@linutronix.de>, Ingo Molnar <mingo@redhat.com>,
        "H. Peter Anvin" <hpa@zytor.com>, x86@kernel.org,
        Borislav Petkov <bp@suse.de>, Viresh Kumar <viresh.kumar@linaro.org>,
        Hidehiro Kawai <hidehiro.kawai.ez@hitachi.com>,
        Len Brown <len.brown@intel.com>,
        "Christopher S. Hall" <christopher.s.hall@intel.com>,
        Adrian Hunter <adrian.hunter@intel.com>, linux-kernel@vger.kernel.org
From: Paolo Bonzini <pbonzini@redhat.com>
Message-ID: <fe5b1c72-2371-bdaa-3f56-dd6e49368d35@redhat.com>
Date: Wed, 13 Jul 2016 15:51:57 +0200
User-Agent: Mozilla/5.0 (X11; Linux x86_64; rv:45.0) Gecko/20100101
 Thunderbird/45.1.1
MIME-Version: 1.0
In-Reply-To: <20160713134900.GU30154@twins.programming.kicks-ass.net>
Content-Type: text/plain; charset=windows-1252
Content-Transfer-Encoding: 7bit
X-Greylist: Sender IP whitelisted, not delayed by milter-greylist-4.5.16 (mx1.redhat.com [10.5.110.27]); Wed, 13 Jul 2016 13:52:04 +0000 (UTC)
Sender: linux-kernel-owner@vger.kernel.org
List-ID: <linux-kernel.vger.kernel.org>
X-Mailing-List: linux-kernel@vger.kernel.org



On 13/07/2016 15:49, Peter Zijlstra wrote:
> On Wed, Jul 13, 2016 at 03:03:42PM +0200, Nicolai Stange wrote:
> 
>>  		clockevents_config_and_register(levt,
>> +						(u32)(((u64)tsc_khz * 1000) /
>> +							TSC_DIVISOR),
>>  						0xF, ~0UL);
> 
> div_u64() perhaps ?

Or just squash together the two patches and do

	tsc_khz * (1000 / TSC_DIVISOR)

because with TSC_DIVISOR equal to 2/4/8 there is no error from
reassociating the operation.

Paolo