From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from mx0a-001b2d01.pphosted.com ([148.163.156.1]:38940 "EHLO mx0a-001b2d01.pphosted.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1725942AbfD0Rpk (ORCPT ); Sat, 27 Apr 2019 13:45:40 -0400 Received: from pps.filterd (m0098394.ppops.net [127.0.0.1]) by mx0a-001b2d01.pphosted.com (8.16.0.27/8.16.0.27) with SMTP id x3RHhCMp013798 for ; Sat, 27 Apr 2019 13:45:39 -0400 Received: from e14.ny.us.ibm.com (e14.ny.us.ibm.com [129.33.205.204]) by mx0a-001b2d01.pphosted.com with ESMTP id 2s4kkmbhgq-1 (version=TLSv1.2 cipher=AES256-GCM-SHA384 bits=256 verify=NOT) for ; Sat, 27 Apr 2019 13:45:39 -0400 Received: from localhost by e14.ny.us.ibm.com with IBM ESMTP SMTP Gateway: Authorized Use Only! Violators will be prosecuted for from ; Sat, 27 Apr 2019 18:45:37 +0100 Date: Sat, 27 Apr 2019 10:45:34 -0700 From: "Paul E. McKenney" Subject: Re: Cost of atomic operations on new hardware Reply-To: paulmck@linux.ibm.com References: MIME-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: Message-Id: <20190427174534.GS3923@linux.ibm.com> Sender: perfbook-owner@vger.kernel.org List-ID: To: Elad Lahav Cc: perfbook@vger.kernel.org On Fri, Apr 26, 2019 at 07:06:10AM -0400, Elad Lahav wrote: > Hello, > > Section 3.1.3 contains the following statement: > > "Fortunately, CPU designers have focused heavily on atomic operations, > so that as of early 2014 they have greatly reduced their overhead." > > My experience with very recent hardware is that the *relative* cost of > atomic operations has actually increased significantly. It seems that > hardware designers, in their attempt to optimize performance for > certain workloads, have produced hardware in which the "anomalous" > conditions (atomic operations, cache misses, barriers, exceptions) > incur much higher penalties than in the past. I assume that this is > primarily the result of more intensive speculation and prediction. Some of the early 2000s systems had -really- atomic operations, but I have not kept close track since 2014. How would you suggest that this be measured? Do you have access to a range of hardweare that would permit us to include something more definite and measurable? Thanx, Paul