Date: Sun, 06 Dec 2009 14:37:15 +0200 From: Alexander Motin <mav@FreeBSD.org> To: Roman Divacky <rdivacky@FreeBSD.org> Cc: svn-src-head@FreeBSD.org, svn-src-all@FreeBSD.org, src-committers@FreeBSD.org Subject: Re: svn commit: r200171 - in head: sbin/atacontrol sys/arm/mv sys/cam/ata sys/cam/scsi sys/conf sys/dev/ata sys/dev/ata/chipsets sys/powerpc/powermac sys/powerpc/psim Message-ID: <4B1BA57B.4070302@FreeBSD.org> In-Reply-To: <20091206115119.GA25721@freebsd.org> References: <200912060010.nB60AD12004058@svn.freebsd.org> <20091206115119.GA25721@freebsd.org>
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Roman Divacky wrote: > On Sun, Dec 06, 2009 at 12:10:13AM +0000, Alexander Motin wrote: >> Author: mav >> Date: Sun Dec 6 00:10:13 2009 >> New Revision: 200171 >> URL: http://svn.freebsd.org/changeset/base/200171 >> >> Log: >> MFp4: >> Introduce ATA_CAM kernel option, turning ata(4) controller drivers into >> cam(4) interface modules. When enabled, this options deprecates all ata(4) >> peripheral drivers (ad, acd, ...) and interfaces and allows cam(4) drivers >> (ada, cd, ...) and interfaces to be natively used instead. >> >> As side effect of this, ata(4) mode setting code was completely rewritten >> to make controller API more strict and permit above change. While doing >> this, SATA revision was separated from PATA mode. It allows DMA-incapable >> SATA devices to operate and makes hw.ata.atapi_dma tunable work again. >> >> Also allow ata(4) controller drivers (except some specific or broken ones) >> to handle larger data transfers. Previous constraint of 64K was artificial >> and is not really required by PCI ATA BM specification or hardware. > > are there any performance benefits of the 64K limit removal? Yes, but it depends on drive and controller. Also it reduces interrupt rate, CPU and command overhead. Also I prefer to have single system-wide tunable for this (MAXPHYS), instead of absolutely ungrounded hardcoded limitation in every driver. -- Alexander Motin
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