Messages in this thread | | | From | "Paul R. Wilson" <> | Date | Mon, 21 Dec 1998 05:28:10 -0600 | Subject | Re: swap cache |
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I think Rama and I are talking about something different from what Rik is talking about. Rather than using compression (only) to increase effective disk bandwidth, a fraction of RAM can be used to hold compressed pages, and avoid paging those out to disk and paging them back in again.
If it is true that the dominant cost of paging is in seeks (and that seems likely) then a compressed page cache is a good idea; it's easy to compress and uncompress a page many times faster than a seek.
BTW, does anybody have suggestions for how to do precise timings inside or outside of the kernel? One of my students wrote some routines that read the Pentium-family instruction-cycle counter, so that we can time things down to a few nanoseconds. (This is how we measure the speed of our compression algorithms in userland.) If there are patches to do this in a better way, though, I'd be very interested. (Or if somebody wanted to use my student's code to implement hi-res time as a patch---maybe implementing Solaris-like gethrtime---Mark gives it away free.)
Are there any plans to support hi-res time in the kernel? I think all the new processors have cycle timers, and that sort of thing is very handy for measuring the performance of system code.
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