Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1762083Ab0HMTJr (ORCPT ); Fri, 13 Aug 2010 15:09:47 -0400 Received: from e5.ny.us.ibm.com ([32.97.182.145]:57662 "EHLO e5.ny.us.ibm.com" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1754565Ab0HMTJq (ORCPT ); Fri, 13 Aug 2010 15:09:46 -0400 Subject: Re: Proposal: Use hi-res clock for file timestamps From: john stultz To: "Patrick J. LoPresti" Cc: linux-fsdevel@vger.kernel.org, linux-nfs@vger.kernel.org, linux-kernel In-Reply-To: References: Content-Type: text/plain; charset="UTF-8" Date: Fri, 13 Aug 2010 12:09:39 -0700 Message-ID: <1281726579.2810.10.camel@localhost.localdomain> Mime-Version: 1.0 X-Mailer: Evolution 2.28.3 Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org Content-Length: 1649 Lines: 41 On Fri, 2010-08-13 at 11:57 -0700, Patrick J. LoPresti wrote: > On Fri, Aug 13, 2010 at 11:45 AM, john stultz wrote: > > On those TSC broken systems that use the hpet or acpi_pm, a > > getnstimeofday call can take 0.5-1.3us, so the penalty can be quite > > severe. > > So you are saying my proposal is a bad idea forever? (But then why > even bother having nanosecond resolution on ext4?) > > Or that it is a bad idea for now? I'm not judging the idea as good/bad, just providing information for context. > Or that it needs to be refined? Maybe use hi-res precision on systems > where it is known to be fast? > > > And even with the TSC, expect some performance impact, as > > reading hardware and doing the multiply is more costly then just > > fetching a value from memory. > > Relative to file system operations? Seriously? What performance hit > would you expect on real-world applications? > Something like 0.1% (10 nsec / 10 usec) worst case? If you can show this does not affect performance in benchmarks, etc, I'm sure it will be easier to push the patch. As outside of performance, I don't think there's much of an issue with the change. So other then "show some numbers", my only thought that might make the patch more attractive is that rather than a global change, or a static CONFIG_ option, would it maybe make more sense as a mount option? thanks -john -- 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/