Re: Any objections/comments on axing out old ATA stack?


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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