Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1751278AbVJNEfk (ORCPT ); Fri, 14 Oct 2005 00:35:40 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1751317AbVJNEfk (ORCPT ); Fri, 14 Oct 2005 00:35:40 -0400 Received: from mx3.mail.elte.hu ([157.181.1.138]:54195 "EHLO mx3.mail.elte.hu") by vger.kernel.org with ESMTP id S1751278AbVJNEfj (ORCPT ); Fri, 14 Oct 2005 00:35:39 -0400 Date: Fri, 14 Oct 2005 06:35:55 +0200 From: Ingo Molnar To: Lee Revell Cc: john stultz , linux-kernel Subject: Re: sched_clock -> check_tsc_unstable -> tsc_read_c3_time ?!? Message-ID: <20051014043555.GA13595@elte.hu> References: <1129233687.16243.52.camel@mindpipe> <1129234306.27168.7.camel@cog.beaverton.ibm.com> <1129234407.16243.58.camel@mindpipe> Mime-Version: 1.0 Content-Type: text/plain; charset=us-ascii Content-Disposition: inline In-Reply-To: <1129234407.16243.58.camel@mindpipe> User-Agent: Mutt/1.4.2.1i X-ELTE-SpamScore: 0.4 X-ELTE-SpamLevel: X-ELTE-SpamCheck: no X-ELTE-SpamVersion: ELTE 2.0 X-ELTE-SpamCheck-Details: score=0.4 required=5.9 tests=AWL,PLING_QUERY autolearn=disabled SpamAssassin version=3.0.3 0.9 PLING_QUERY Subject has exclamation mark and question mark -0.4 AWL AWL: From: address is in the auto white-list X-ELTE-VirusStatus: clean Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1061 Lines: 25 * Lee Revell wrote: > On Thu, 2005-10-13 at 13:11 -0700, john stultz wrote: > > Yea, you're right about the inlining. Although I'm not sure why those > > functions should take microseconds to execute. That's very strange. > > Latency tracing overhead plus a slow (600MHz) machine? yeah. The micro-timings of latency tracing can be misleading. Function calls are very fast on most CPUs (even on a 600MHz one), but with the latency tracer generating one trace entry per function call, there's considerable added overhead. we could in theory calibrate the tracing overhead and subtract it from cycle readings [i've done this in a previous mcount() based tracer implementation, years ago], but that would make the latency trace timestamps less useful as a global time reference. Ingo - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/