[ On Friday, June 21, 2002 at 13:53:33 (-0400), Gary Thorpe wrote: ]
> Subject: Re: I/O priorities
>
> The original poster said the behaviour was only noticeable in 1.6, which has 
> UBC and not in 1.5.2 which does not. Since BOTH of these releases use the 
> SAME disk scheduling algorithm (yes?), the problem is not with CSCAN vs. 
> elevator vs. whatever disk scheduling algorithm. Major difference: 1.5.2 has 
> a FIXED size buffer and a FIXED sized cache while UBC has a variable size 
> combined scheme (yes?). Perhaps in 1.5.2 the FIXED sizes provide some 
> predefined means of limiting I/O requests, while in 1.6 the variable size 
> has lead to the overlooking of a new mechanism for limiting I/O requests 
> (which must be determined dynamically at run time depending on load etc.).

I think that's a fairly accurate analysis -- the only thing missing
being that the poster had adjusted various cache sizes and min/max
parameters from their default, but I don't think that detracts from the
fact that it's now easier to batch up enough I/O requests such that some
interactive response might suffer should the system be generally starved
for resources.

-- 
								Greg A. Woods

+1 416 218-0098;  <gwoods@acm.org>;  <g.a.woods@ieee.org>;  <woods@robohack.ca>
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