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Date:      Sun, 29 Nov 2009 17:47:08 -0700
From:      Scott Long <scottl@samsco.org>
To:        Scott Long <scottl@samsco.org>
Cc:        Attilio Rao <attilio@freebsd.org>, arch@freebsd.org, Julian Elischer <julian@elischer.org>
Subject:   Re: sglist(9)
Message-ID:  <615AB9D0-7171-4FE1-BE38-74E6FA7FE93A@samsco.org>
In-Reply-To: <F39A82E9-36B0-40F1-B3DA-08843A5799F3@samsco.org>
References:  <200905191458.50764.jhb@freebsd.org>	<alpine.BSF.2.00.0905200841230.981@desktop>	<200905201522.58501.jhb@freebsd.org>	<3bbf2fe10911291429k54b4b7cfw9e40aefeca597307@mail.gmail.com> <66707B0F-D0AB-49DB-802F-13146F488E1A@samsco.org> <4B130C6A.70406@elischer.org> <F39A82E9-36B0-40F1-B3DA-08843A5799F3@samsco.org>

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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




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