announce: PPSkit patch for Linux 2.4.2 (pre6)
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Followup to: <3AD2CE98.28151.46E93A@localhost> By author: "Ulrich Windl" <[email protected]> In newsgroup: linux.dev.kernel
Quoted 8 lines
Hi, Cycle Counters,
Linux currently tries to synchronize TSCs for consistent time in SMP systems. One would not believe what combinations of hardware are tried, especially for precision timing. Here's a short answer to my asking- back about a complaint (the kernel is reporting negative time warps).
Quoted 9 lines
As any problem, it can be solved with some overhead, but should it be done?
Replies to me too, as I'm not subscribed, please.
Quoted 4 lines
I have to tell you that I have one 533 MHz Celeron and one 433 MHz Celeron.
Hi there,
We have talked about assymmetric multiprocessor configurations once or twice around. The easy way to deal with them is simply to use "no-tsc" on the command line (and/or compile your kernel appropriately.) One could, at least theoretically, make them usable in kernel space only (in user space there is no hope, since you can't know which CPU's TSC you're reading), but these machines seem to be so rare that hardly anyone technical enough to fix it cares.
-hpa
Signature · 3 lines
<[email protected]> at work, <[email protected]> in private! "Unix gives you enough rope to shoot yourself in the foot." http://www.zytor.com/~hpa/puzzle.txt
Quoted 4 lines
appropriately.) One could, at least theoretically, make them usable in kernel space only (in user space there is no hope, since you can't know which CPU's TSC you're reading), but these machines seem to be so rare that hardly anyone technical enough to fix it cares.
Im working on making the 'notsc' automatic. Trying to 'fix' it is just plain hard work. With the fixed one however we can still use the tsc for udelay as we have per cpu loops_per_jiffy data.
This btw is why -ac figures out the bus multiplier on your processors. If they dont match then we know tsc wants to be off. Just nobody has written the code to disable it across all CPUs yet
Quoted 6 lines · Alan Cox
Quoted 5 lines
appropriately.) One could, at least theoretically, make them usable in kernel space only (in user space there is no hope, since you can't know which CPU's TSC you're reading), but these machines seem to be so rare that hardly anyone technical enough to fix it cares.
Quoted 8 lines
Im working on making the 'notsc' automatic. Trying to 'fix' it is just plain hard work. With the fixed one however we can still use the tsc for udelay as we have per cpu
loops_per_jiffydata.This btw is why -ac figures out the bus multiplier on your processors. If they dont match then we know tsc wants to be off. Just nobody has written the code to disable it across all CPUs yet
Yes, there are two cases where we can "fix" it: in the timer interrupt code, and the loops_per_jiffy stuff.
-hpa
Signature · 3 lines
<[email protected]> at work, <[email protected]> in private! "Unix gives you enough rope to shoot yourself in the foot." http://www.zytor.com/~hpa/puzzle.txt