On Thu, Mar 18, 2004 at 08:17:00PM -0800, David Brownell wrote:Pat LaVarre wrote:
Agreed, shattering a read/ write stream into miniscule pieces improves interop at small cost to typical usage of much storage.
It improves interop, yes ... but that cost would only be small for full speed devices. It's called "de-tuning", or "pessimizing" (contrast "optimizing").
For devices that work properly -- like the high speed ISD bridges, Western Digital drives I've tried, and many others -- it's better not to force use of mini-transactions. Make whitelisted hardware run at its natural speed by default: no fragment limits, use the system's low level flow control mechanisms as they're intended.
Given the pain we've had with maintaining the unusual_devs.h device list, I'm very reluctant to start another list (even if it is a 'whitelist').
Well, since you're suggesting Linux slow things down significantly by default, I'd want to see a better answer than "end-users can manually make them fast again" ... as we know, end-users don't read the docs, and frankly they shouldn't need to.
Note that such a whitelist wouldn't be the same kind of hassle as growing a quirk list (like unusual_devs.h) ... the downside of not putting a device into that whitelist would be that it's needlessly slow to access the device. It'd still work. (Whereas devices go into the quirk list specifically _because_ they don't work right.)
Of course, "breaks at rated speed" could be a quirk too ... and if Linux emitted a message for those devices, maybe their vendors would eventually get the message, by loss-of-customers! :)
Don't get me wrong, I really do know what a PITA it is to need to maintain lists of device quirks ... although my personal experience is with much smaller lists!
But I also think that one of the very nice things about Linux is that it's able to get better performance out of hardware than "that other OS". So policies which throw away those benefits, in common cases when there's no need, seem unattractive to me.
- Dave
Matt
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