From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1754504Ab0KBCVX (ORCPT ); Mon, 1 Nov 2010 22:21:23 -0400 Received: from usmamail.tilera.com ([72.1.168.231]:40480 "EHLO USMAMAIL.TILERA.COM" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1752783Ab0KBCVW (ORCPT ); Mon, 1 Nov 2010 22:21:22 -0400 Message-ID: <4CCF759A.2010206@tilera.com> Date: Mon, 1 Nov 2010 22:21:15 -0400 From: Chris Metcalf User-Agent: Mozilla/5.0 (Windows; U; Windows NT 5.1; en-US; rv:1.9.2.12) Gecko/20101027 Thunderbird/3.1.6 MIME-Version: 1.0 To: CC: , Subject: Re: [PATCH] drivers/char/hvc_console.c: reduce max idle timeout References: <201010271659.o9RGxrMc009847@farm-0002.internal.tilera.com> <1288658108.16790.13.camel@concordia> In-Reply-To: <1288658108.16790.13.camel@concordia> Content-Type: text/plain; charset="UTF-8" Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org List-ID: X-Mailing-List: linux-kernel@vger.kernel.org On 11/1/2010 8:35 PM, Michael Ellerman wrote: > On Wed, 2010-10-27 at 12:54 -0400, Chris Metcalf wrote: >> The tile architecture uses this framework for our serial console, >> and our users complain that the delay of up to two seconds feels like >> the machine has gone non-responsive and is disturbing. By contrast, >> a delay of up to half a second feels like just the normal sort of >> delay caused by swapping, network lag, etc. and is not noticeable. >> The overhead is obviously not much greater. > It's 4 times greater. > > We picked 2 seconds because it gave a reasonable trade off between > responsiveness and load. I'm not convinced that half a second is a > better number. Perhaps the tradeoff should be tunable, then? I think on our architecture we're willing to pay a higher cost on the core running this task, since we have many cores; we often have a core that mostly just runs miscellaneous Linux administrative tasks anyway, so adding a bit more overhead there is not significant for us. This issue has caused multiple reports of unresponsiveness from our users, so I'd be interested in finding a way to strike a balance. We could use a config option defaulting to 2 seconds (for example), or something more dynamic (probably unnecessary). Let me know your preference, if this sounds plausible, and I'll write up a proposed patch. Thanks. -- Chris Metcalf, Tilera Corp. http://www.tilera.com From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from USMAMAIL.TILERA.COM (usmamail.tilera.com [72.1.168.231]) (using TLSv1 with cipher AES128-SHA (128/128 bits)) (Client CN "usmamail.tilera.com", Issuer "Go Daddy Secure Certification Authority" (verified OK)) by ozlabs.org (Postfix) with ESMTPS id 12D6DB6F07 for ; Tue, 2 Nov 2010 13:21:34 +1100 (EST) Message-ID: <4CCF759A.2010206@tilera.com> Date: Mon, 1 Nov 2010 22:21:15 -0400 From: Chris Metcalf MIME-Version: 1.0 To: Subject: Re: [PATCH] drivers/char/hvc_console.c: reduce max idle timeout References: <201010271659.o9RGxrMc009847@farm-0002.internal.tilera.com> <1288658108.16790.13.camel@concordia> In-Reply-To: <1288658108.16790.13.camel@concordia> Content-Type: text/plain; charset="UTF-8" Cc: linuxppc-dev@lists.ozlabs.org, linux-kernel@vger.kernel.org List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On 11/1/2010 8:35 PM, Michael Ellerman wrote: > On Wed, 2010-10-27 at 12:54 -0400, Chris Metcalf wrote: >> The tile architecture uses this framework for our serial console, >> and our users complain that the delay of up to two seconds feels like >> the machine has gone non-responsive and is disturbing. By contrast, >> a delay of up to half a second feels like just the normal sort of >> delay caused by swapping, network lag, etc. and is not noticeable. >> The overhead is obviously not much greater. > It's 4 times greater. > > We picked 2 seconds because it gave a reasonable trade off between > responsiveness and load. I'm not convinced that half a second is a > better number. Perhaps the tradeoff should be tunable, then? I think on our architecture we're willing to pay a higher cost on the core running this task, since we have many cores; we often have a core that mostly just runs miscellaneous Linux administrative tasks anyway, so adding a bit more overhead there is not significant for us. This issue has caused multiple reports of unresponsiveness from our users, so I'd be interested in finding a way to strike a balance. We could use a config option defaulting to 2 seconds (for example), or something more dynamic (probably unnecessary). Let me know your preference, if this sounds plausible, and I'll write up a proposed patch. Thanks. -- Chris Metcalf, Tilera Corp. http://www.tilera.com