Date: Thu, 28 Mar 2013 09:01:57 -0700 From: Matthew Jacob <mj@feral.com> To: freebsd-current@freebsd.org Subject: Re: Any objections/comments on axing out old ATA stack? Message-ID: <51546975.3050103@feral.com> In-Reply-To: <C92954BE-0E4A-49D2-9D58-325E78A2B304@samsco.org> References: <51536306.5030907@FreeBSD.org> <51536EFD.4060202@freebsd.org> <C92954BE-0E4A-49D2-9D58-325E78A2B304@samsco.org>
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On 3/28/2013 8:27 AM, Scott Long wrote: > On Mar 27, 2013, at 4:13 PM, Matthew Jacob <mjacob@FreeBSD.org> wrote: > >> On 3/27/2013 2:22 PM, Alexander Motin wrote: >>> Hi. >>> >>> Since FreeBSD 9.0 we are successfully running on the new CAM-based ATA stack, using only some controller drivers of old ata(4) by having `options ATA_CAM` enabled in all kernels by default. I have a wish to drop non-ATA_CAM ata(4) code, unused since that time from the head branch to allow further ATA code cleanup. >>> >>> Does any one here still uses legacy ATA stack (kernel explicitly built without `options ATA_CAM`) for some reason, for example as workaround for some regression? Does anybody have good ideas why we should not drop it now? >>> >> Some people have expressed performance concerns about ATA_CAM. I have not validated those concerns. Does anyone know of any? > The albatross of "CAM is slow" comes up over and over, but I never see any data to support the claims. So here's an anecdote of my own. > Yes, I understand that. Like I said, they didn't give me details about it, but it did seem like some data they were throwing around showed a falloff that was significant. However, they have a number of other differences which, for whatever reason, may not have played well. I'm waiting for more info on it.
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