From owner-freebsd-arch@FreeBSD.ORG Sun Mar 21 15:46:57 2010 Return-Path: Delivered-To: freebsd-arch@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id 26798106566B; Sun, 21 Mar 2010 15:46:57 +0000 (UTC) (envelope-from julian@elischer.org) Received: from out-0.mx.aerioconnect.net (out-0-5.mx.aerioconnect.net [216.240.47.65]) by mx1.freebsd.org (Postfix) with ESMTP id ABC138FC24; Sun, 21 Mar 2010 15:46:56 +0000 (UTC) Received: from idiom.com (postfix@mx0.idiom.com [216.240.32.160]) by out-0.mx.aerioconnect.net (8.13.8/8.13.8) with ESMTP id o2LFktDv015391; Sun, 21 Mar 2010 08:46:55 -0700 X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e X-Client-Authorized: MaGic Cook1e Received: from julian-mac.elischer.org (h-67-100-89-137.snfccasy.static.covad.net [67.100.89.137]) by idiom.com (Postfix) with ESMTP id 63C4B2D601C; Sun, 21 Mar 2010 08:46:55 -0700 (PDT) Message-ID: <4BA63F72.5000806@elischer.org> Date: Sun, 21 Mar 2010 08:46:58 -0700 From: Julian Elischer User-Agent: Thunderbird 2.0.0.24 (Macintosh/20100228) MIME-Version: 1.0 To: Alexander Motin References: <4BA4E7A9.3070502@FreeBSD.org> <201003201753.o2KHrH5x003946@apollo.backplane.com> <891E2580-8DE3-4B82-81C4-F2C07735A854@samsco.org> <4BA52179.9030903@FreeBSD.org> <4BA532FF.6040407@elischer.org> <4BA62757.7090400@FreeBSD.org> In-Reply-To: <4BA62757.7090400@FreeBSD.org> Content-Type: text/plain; charset=ISO-8859-1; format=flowed Content-Transfer-Encoding: 7bit X-Scanned-By: MIMEDefang 2.67 on 216.240.47.51 Cc: Scott Long , FreeBSD-Current , freebsd-arch@freebsd.org Subject: Re: Increasing MAXPHYS X-BeenThere: freebsd-arch@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussion related to FreeBSD architecture List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Sun, 21 Mar 2010 15:46:57 -0000 Alexander Motin wrote: > Julian Elischer wrote: >> In the Fusion-io driver we find that the limiting factor is not the >> size of MAXPHYS, but the fact that we can not push more than >> 170k tps through geom. (in my test machine. I've seen more on some >> beefier machines), but that is only a limit on small transacrtions, >> or in the case of large transfers the DMA engine tops out before a >> bigger MAXPHYS would make any difference. > > Yes, GEOM is quite CPU-hungry on high request rates due to number of > context switches. But impact probably may be reduced from two sides: by > reducing overhead per request, or by reducing number of requests. Both > ways may give benefits. > > If common opinion is not to touch defaults now - OK, agreed. (Note, > Scott, I have agreed :)) But returning to the original question, does > somebody knows real situation when increased MAXPHYS still causes > problems? At least to make it safe. well I know we havn't tested our bsd driver yet with MAXPHYS > 128KB at this time.. Must try that some time :-)