From owner-freebsd-current@FreeBSD.ORG Mon Mar 22 00:54:42 2010 Return-Path: Delivered-To: freebsd-current@freebsd.org Received: from mx1.freebsd.org (mx1.freebsd.org [IPv6:2001:4f8:fff6::34]) by hub.freebsd.org (Postfix) with ESMTP id E0DE8106566B; Mon, 22 Mar 2010 00:54:41 +0000 (UTC) (envelope-from jhellenthal@gmail.com) Received: from mail-vw0-f54.google.com (mail-vw0-f54.google.com [209.85.212.54]) by mx1.freebsd.org (Postfix) with ESMTP id 11FAA8FC18; Mon, 22 Mar 2010 00:54:40 +0000 (UTC) Received: by vws1 with SMTP id 1so184060vws.13 for ; Sun, 21 Mar 2010 17:54:40 -0700 (PDT) DKIM-Signature: v=1; a=rsa-sha256; c=relaxed/relaxed; d=gmail.com; s=gamma; h=domainkey-signature:received:received:sender:date:from:to:cc :subject:in-reply-to:message-id:references:user-agent :x-openpgp-key-id:x-openpgp-key-fingerprint:mime-version :content-type; bh=CCBCoeSdGBY5/LyK2DKG78COsETPwjg37vGlqWHzStQ=; b=PSE7OuLEr2Jxa5KYNcqCDtnRyIqlGqcND5j2JU4zlyC9HC/UVRHzbqrBZkBrP2I1pf 25PehvLVVukCOgIlpx5+mE0yQr22sATFpyMqKXxxm3giWGvwziIFD1tD/eblNtSc6avv /lezHJlrjuyCklvHuo+MB/EgppyeDNh8U0/l8= DomainKey-Signature: a=rsa-sha1; c=nofws; d=gmail.com; s=gamma; h=sender:date:from:to:cc:subject:in-reply-to:message-id:references :user-agent:x-openpgp-key-id:x-openpgp-key-fingerprint:mime-version :content-type; b=cXocjCDcbsteYexf+YwfKw9zmsEdzaZpuvYOF+XMjMcMjFAF39EFsoCbv7jw3VO2eV byCTnhU431KFGd6lJZQ/Ww31YqgYoH4rnYDdEX5yE+KbN1OwxpUkKCo/Dy3kJuTdqvZe 1KlH1LgyaN6uCa/iJphGt4wTALo+KEjf5thsc= Received: by 10.220.126.222 with SMTP id d30mr2983568vcs.198.1269219280436; Sun, 21 Mar 2010 17:54:40 -0700 (PDT) Received: from ppp-21.206.dialinfree.com (ppp-21.206.dialinfree.com [209.172.21.206]) by mx.google.com with ESMTPS id 21sm30691517vws.2.2010.03.21.17.54.36 (version=TLSv1/SSLv3 cipher=RC4-MD5); Sun, 21 Mar 2010 17:54:39 -0700 (PDT) Sender: "J. Hellenthal" Date: Sun, 21 Mar 2010 20:54:59 -0400 From: jhell To: Alexander Motin In-Reply-To: <4BA62757.7090400@FreeBSD.org> Message-ID: 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> User-Agent: Alpine 2.00 (BSF 1167 2008-08-23) X-OpenPGP-Key-Id: 0x89D8547E X-OpenPGP-Key-Fingerprint: 85EF E26B 07BB 3777 76BE B12A 9057 8789 89D8 547E MIME-Version: 1.0 Content-Type: TEXT/PLAIN; charset=US-ASCII; format=flowed Cc: FreeBSD-Current , Julian Elischer , freebsd-arch@freebsd.org Subject: Re: Increasing MAXPHYS X-BeenThere: freebsd-current@freebsd.org X-Mailman-Version: 2.1.5 Precedence: list List-Id: Discussions about the use of FreeBSD-current List-Unsubscribe: , List-Archive: List-Post: List-Help: List-Subscribe: , X-List-Received-Date: Mon, 22 Mar 2010 00:54:42 -0000 On Sun, 21 Mar 2010 10:04, mav@ 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. > > I played with it on one re-compile of a kernel and for the sake of it DFLTPHYS=128 MAXPHYS=256 and found out that I could not cause a crash dump to be performed upon request (reboot -d) due to the boundary being hit for DMA which is 65536. Obviously this would have to be adjusted in ata-dma.c. I suppose that there would have to be a better way to get the real allowable boundary from the running system instead of setting it statically. Other then the above I do not see a reason why not... It is HEAD and this is the type of experimental stuff it was meant for. Regards, -- jhell