Messages in this thread | | | Date | Mon, 05 Mar 2007 10:32:22 -0500 | From | Bill Davidsen <> | Subject | Re: [PATCH] libata: warn if speed limited due to 40-wire cable (v2) |
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Stephen Clark wrote: > Bill Davidsen wrote: > >> Stephen Clark wrote: >> >> >>> Bill Davidsen wrote: >>> >>> >>>> Alan Cox wrote: >>>> >>>> >>>> >>>>>> it seems broken to manipulate xfer_mask after returning from the >>>>>> driver's ->mode_filter hook. >>>>>> >>>>>> this patch is more than just a speed-limited warning printk, afaics >>>>>> >>>>> I actually suggested that order because the only way the printk >>>>> can be >>>>> done correctly is for it to be the very last test made. Since the >>>>> mode >>>>> filter is not told what mode will be used but just subtracts modes >>>>> that >>>>> are not allowed this should be safe. >>>>> >>>>> >>>> Far better to have a drive which works slowly than one which works >>>> unreliably. >>>> >>>> >>>> >>>> >>> That would be true if the 40 wire detection was 100% accurate! >>> >> The statement is completely correct, even though the detection may >> not be. ;-) >> >> With the current set(s) of patches to do better detection, cable >> evaluation should be better. But even if not, a slow system is more >> useful than one which doesn't work, crashes because of swap i/o >> errors, etc. >> >> >> > I have had problems with cable detection on my previous laptop and my > current laptop. It almost made > my systems unusable. On my current laptop I was getting a thruput of a > little over 1 mbps instead > of the 44 mbps I get with udma set to the correct value. It took hours > to upgrade my laptop from > fc5 to fc6 because of this mis detection. > As far as I can see, if you are getting that low a speed, you have other problems. I have a system with old slow drives which are really on a 40 pin cable, and they run at UDMA(33). One of the experts in this can undoubtedly tell us more, but your system should run faster than that, mine does, and I really HAVE a 40 pin cable (and drive).
If your system drops to PIO modes, I doubt cable is the only issue, I think there are other issues (acpi comes to mind).
-- bill davidsen <davidsen@tmr.com> CTO TMR Associates, Inc Doing interesting things with small computers since 1979
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