From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: from smtp2.linux-foundation.org (smtp2.linux-foundation.org [207.189.120.14]) (using TLSv1 with cipher DHE-RSA-AES256-SHA (256/256 bits)) (Client CN "smtp.osdl.org", Issuer "CA Cert Signing Authority" (verified OK)) by ozlabs.org (Postfix) with ESMTP id B0C7BDDDFF for ; Wed, 23 May 2007 06:21:41 +1000 (EST) Date: Tue, 22 May 2007 13:08:24 -0700 From: Andrew Morton To: Maxim Uvarov Subject: Re: [PATCH] Performance Stats: Kernel patch Message-Id: <20070522130824.a78976aa.akpm@linux-foundation.org> In-Reply-To: <20070522171950.23728.95735.stgit@localhost.localdomain> References: <20070522171950.23728.95735.stgit@localhost.localdomain> Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Cc: linuxppc-dev@ozlabs.org, LKML List-Id: Linux on PowerPC Developers Mail List List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , On Tue, 22 May 2007 17:19:52 +0000 Maxim Uvarov wrote: > Sorry for bothering you. I know you are very busy but could > you please tell me what is situation of this patch? I'd like to add the context-switch accounting to the taskstats payload. As we'd then need to uprev the taskstats payload and version it makes sense to have a look around, see if there's anything else which should be in there but got missed. I don't think we can accept the number-of-syscalls accounting feature. It adds a memory increment into the kernel's number-one hotpath. Something which people like to obsessively microbenchmark. And as I said earlier, a 32-bit counter can be overflowed in mere seconds, so that needs to become 64-bit, in which case we add a memory increment and a test-n-branch to that hottest path. There _is_ some cumulative overhead here, and I don't see how the value of the syscall counter can justify it. From mboxrd@z Thu Jan 1 00:00:00 1970 Return-Path: Received: (majordomo@vger.kernel.org) by vger.kernel.org via listexpand id S1759006AbXEVUKd (ORCPT ); Tue, 22 May 2007 16:10:33 -0400 Received: (majordomo@vger.kernel.org) by vger.kernel.org id S1755936AbXEVUK0 (ORCPT ); Tue, 22 May 2007 16:10:26 -0400 Received: from smtp2.linux-foundation.org ([207.189.120.14]:33302 "EHLO smtp2.linux-foundation.org" rhost-flags-OK-OK-OK-OK) by vger.kernel.org with ESMTP id S1755346AbXEVUKZ (ORCPT ); Tue, 22 May 2007 16:10:25 -0400 Date: Tue, 22 May 2007 13:08:24 -0700 From: Andrew Morton To: Maxim Uvarov Cc: LKML , Subject: Re: [PATCH] Performance Stats: Kernel patch Message-Id: <20070522130824.a78976aa.akpm@linux-foundation.org> In-Reply-To: <20070522171950.23728.95735.stgit@localhost.localdomain> References: <20070522171950.23728.95735.stgit@localhost.localdomain> X-Mailer: Sylpheed version 2.2.7 (GTK+ 2.8.6; i686-pc-linux-gnu) Mime-Version: 1.0 Content-Type: text/plain; charset=US-ASCII Content-Transfer-Encoding: 7bit Sender: linux-kernel-owner@vger.kernel.org X-Mailing-List: linux-kernel@vger.kernel.org On Tue, 22 May 2007 17:19:52 +0000 Maxim Uvarov wrote: > Sorry for bothering you. I know you are very busy but could > you please tell me what is situation of this patch? I'd like to add the context-switch accounting to the taskstats payload. As we'd then need to uprev the taskstats payload and version it makes sense to have a look around, see if there's anything else which should be in there but got missed. I don't think we can accept the number-of-syscalls accounting feature. It adds a memory increment into the kernel's number-one hotpath. Something which people like to obsessively microbenchmark. And as I said earlier, a 32-bit counter can be overflowed in mere seconds, so that needs to become 64-bit, in which case we add a memory increment and a test-n-branch to that hottest path. There _is_ some cumulative overhead here, and I don't see how the value of the syscall counter can justify it.