* Re: announce: PPSkit patch for Linux 2.4.2 (pre6) [not found] ` <3AC83FF1.27420.398B86@localhost> @ 2001-04-10 7:12 ` Ulrich Windl 2001-04-11 17:56 ` H. Peter Anvin 0 siblings, 1 reply; 4+ messages in thread From: Ulrich Windl @ 2001-04-10 7:12 UTC (permalink / raw) To: linux-kernel 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). 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. Ulrich On 9 Apr 2001, at 18:39, Andreas Bussjaeger wrote: > > from the current CPU. All these values seem highly suspect. However a > > few more values would be helpful to diagnose the situation. > > I have to tell you that I have one 533 MHz Celeron and one 433 MHz > Celeron. > > > indicate that the CPUs are 968ms apart (each CPU half from the average). ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: announce: PPSkit patch for Linux 2.4.2 (pre6) 2001-04-10 7:12 ` announce: PPSkit patch for Linux 2.4.2 (pre6) Ulrich Windl @ 2001-04-11 17:56 ` H. Peter Anvin 2001-04-11 18:03 ` Alan Cox 0 siblings, 1 reply; 4+ messages in thread From: H. Peter Anvin @ 2001-04-11 17:56 UTC (permalink / raw) To: linux-kernel Followup to: <3AD2CE98.28151.46E93A@localhost> By author: "Ulrich Windl" <Ulrich.Windl@rz.uni-regensburg.de> In newsgroup: linux.dev.kernel > > 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). > > 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. > > > > > 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 -- <hpa@transmeta.com> at work, <hpa@zytor.com> in private! "Unix gives you enough rope to shoot yourself in the foot." http://www.zytor.com/~hpa/puzzle.txt ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: announce: PPSkit patch for Linux 2.4.2 (pre6) 2001-04-11 17:56 ` H. Peter Anvin @ 2001-04-11 18:03 ` Alan Cox 2001-04-11 18:18 ` H. Peter Anvin 0 siblings, 1 reply; 4+ messages in thread From: Alan Cox @ 2001-04-11 18:03 UTC (permalink / raw) To: H. Peter Anvin; +Cc: linux-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. 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 ^ permalink raw reply [flat|nested] 4+ messages in thread
* Re: announce: PPSkit patch for Linux 2.4.2 (pre6) 2001-04-11 18:03 ` Alan Cox @ 2001-04-11 18:18 ` H. Peter Anvin 0 siblings, 0 replies; 4+ messages in thread From: H. Peter Anvin @ 2001-04-11 18:18 UTC (permalink / raw) To: Alan Cox; +Cc: H. Peter Anvin, linux-kernel Alan Cox wrote: > > > 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 > Yes, there are two cases where we can "fix" it: in the timer interrupt code, and the loops_per_jiffy stuff. -hpa -- <hpa@transmeta.com> at work, <hpa@zytor.com> in private! "Unix gives you enough rope to shoot yourself in the foot." http://www.zytor.com/~hpa/puzzle.txt ^ permalink raw reply [flat|nested] 4+ messages in thread
end of thread, other threads:[~2001-04-11 18:19 UTC | newest]
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2001-04-10 7:12 ` announce: PPSkit patch for Linux 2.4.2 (pre6) Ulrich Windl
2001-04-11 17:56 ` H. Peter Anvin
2001-04-11 18:03 ` Alan Cox
2001-04-11 18:18 ` H. Peter Anvin
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