From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp.ispras.ru (winnie.ispras.ru [83.149.199.91]) by sourceware.org (Postfix) with ESMTP id 77B613851C0F for ; Tue, 19 May 2020 21:18:23 +0000 (GMT) DMARC-Filter: OpenDMARC Filter v1.3.2 sourceware.org 77B613851C0F Received: from monopod.intra.ispras.ru (monopod.intra.ispras.ru [10.10.3.121]) by smtp.ispras.ru (Postfix) with ESMTP id 6D816203BF; Wed, 20 May 2020 00:18:22 +0300 (MSK) Date: Wed, 20 May 2020 00:18:22 +0300 (MSK) From: Alexander Monakov To: "H.J. Lu" cc: libc-alpha@sourceware.org Subject: Re: [PATCH] benchtests: Restore the clock_gettime option In-Reply-To: <20200519203053.9854-1-hjl.tools@gmail.com> Message-ID: References: <20200519203053.9854-1-hjl.tools@gmail.com> User-Agent: Alpine 2.20.13 (LNX 116 2015-12-14) MIME-Version: 1.0 Content-Type: text/plain; charset=US-ASCII X-Spam-Status: No, score=-7.5 required=5.0 tests=BAYES_00, KAM_DMARC_STATUS, SPF_HELO_NONE, SPF_PASS, TXREP autolearn=ham autolearn_force=no version=3.4.2 X-Spam-Checker-Version: SpamAssassin 3.4.2 (2018-09-13) on server2.sourceware.org X-BeenThere: libc-alpha@sourceware.org X-Mailman-Version: 2.1.29 Precedence: list List-Id: Libc-alpha mailing list List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Tue, 19 May 2020 21:18:25 -0000 On Tue, 19 May 2020, H.J. Lu via Libc-alpha wrote: > commit 7621e38bf3c58b2d0359545f1f2898017fd89d05 > Author: Wilco Dijkstra > Date: Tue Jan 29 17:43:45 2019 +0000 > > Add generic hp-timing support > > removed the clock_gettime option. On x86, fewer cycles doesn't > necessarily mean faster exection due to frequency drop. We should > restore the clock_gettime option. Can you please elaborate more which x86 CPUs you have in mind here, as since Nehalem (2008) when invariant TSC was introduced, the rdtsc(p) instructions count at a fixed rate rather than at CPU clock rate. And before 2008, there were no turbo frequencies and no AVX frequency drop. Alexander