Date: Sun, 29 Nov 2009 17:40:12 -0700 From: Scott Long <scottl@samsco.org> To: Julian Elischer <julian@elischer.org> Cc: Attilio Rao <attilio@freebsd.org>, arch@freebsd.org Subject: Re: sglist(9) Message-ID: <F39A82E9-36B0-40F1-B3DA-08843A5799F3@samsco.org> In-Reply-To: <4B130C6A.70406@elischer.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>
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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. Scott
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