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From: Scott Long <scottl@samsco.org>
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To: Scott Long <scottl@samsco.org>
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Cc: Attilio Rao <attilio@freebsd.org>, arch@freebsd.org,
	Julian Elischer <julian@elischer.org>
Subject: Re: sglist(9)
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On Nov 29, 2009, at 5:40 PM, Scott Long wrote:
> On Nov 29, 2009, at 5:06 PM, Julian Elischer wrote:
>> Scott Long wrote:
>>
>>> I think this is fundamentally wrong.  You're proposing exchanging  
>>> a cheap operation of splitting VA's with an expensive operation of  
>>> allocating, splitting, copying, and refcounting sglists.   
>>> Splitting is an excessively common operation, and your proposal  
>>> will impact performance as storage becomes exponentially faster.
>>
>> From the perspective of a flashdrive driver the more
>> efficient the better. The current generation of devices are
>> doing 800MB/sec (6.4Gb/sec) of scattter-gather random IO
>> and really that will only go up. We are doing over 130,000  
>> independent
>> transactions per second and we can put multiple drives in a single
>> machine.
>>
>> These numbers will only increase with future developments.
>
> MB/s doesn't tell me much other than the memory bandwidth of the  
> pathways (and that that DMA engines involved don't completely  
> suck).  What about transactions/sec?  That tells me a lot more about  
> the efficiency of the OS, drivers, and firmware, as well as latency.
>
>

Bah, the answer was right in front of me, sorry =-)  130k is impressive.

Scott