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Message-ID: <465F59BB.9040909@garzik.org> Date: Thu, 31 May 2007 19:26:51 -0400 From: Jeff Garzik <jeff@...zik.org> To: Mark Lord <liml@....ca> CC: Daniel J Blueman <daniel.blueman@...il.com>, bzolnier@...il.com, linux-ide@...r.kernel.org, Linux Kernel <linux-kernel@...r.kernel.org>, Alan Cox <alan@...rguk.ukuu.org.uk> Subject: Re: Compact Flash performance... Mark Lord wrote: > To maximize throughput, some kind of host-queuing would be needed, > or just have the driver sit in a tight loop, starting the next I/O > immediately when the previous one finishes. Linux isn't that quick (yet). I was talking on IRC with Tejun just recently. There are several controllers (and/or "situations") like this, where some amount of host queueing would permit greater throughput, even when NCQ is not supported. sata_sx4 is the most dramatic example, where host queueing could potentially increase speed by a factor of 10 or more, since it is penalized by an awful two-irq-per-command (w/ a per-host bottleneck to boot) setup. Silicon Image has a "command buffer". And overall, I designed ->qc_prep() hook separate from ->qc_issue() to enable the prepartion of multiple commands such that it only takes a simple "go" I/O to start a transaction, immediately after the previous one ends. Jeff - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@...r.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
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