Re: Fastest timecounter ?
On Mon, Feb 27, 2006 at 06:09:26PM +0200, Vlad GALU wrote: I wrote a piece of software that has to get the current timestamp, one way or the other, a huge number of times per second. Apart from the empyrical tests one can perform to find out the timekeeping scheme with the less performance impact, is there any rule of thumb as to what choice to go for ? The TSC is always fastest, but unfortunately under some circumstances it can't be trusted (if your CPU has throttle modes to save power or on some SMP systems where the two TSCs in each CPU give different values). David. ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Re: Fastest timecounter ?
From: David Malone [EMAIL PROTECTED] The TSC is always fastest, but unfortunately under some circumstances it can't be trusted (if your CPU has throttle modes to save power or on some SMP systems where the two TSCs in each CPU give different values). If I remember correctly, all the SMP CPUs on the same bus should give the same values (since they are synchronized and reset from the same signals). The discrepancy may appear on machines with multiple bridged front-side buses, essentially the NUMA machines (such as those with over 4 Intel CPUs). -SB ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to [EMAIL PROTECTED]
Re: Fastest timecounter ?
vg I wrote a piece of software that has to get the current vg timestamp, one way or the other, a huge number of times per vg second. Apart from the empyrical tests one can perform to vg find out the timekeeping scheme with the less performance vg impact, is there any rule of thumb as to what choice to go vg for ? vg Any kind of advice is most welcome, especially reading vg material. vg P.S. I know that some of you may say that calling vg gettimeofday() that often is braindead, and at some vg point I agree. Unfortunatley, right now I can't do vg anything better. I need timekeeping to comb the vg algorithms that deal with my data structures a bit more, vg after which I can switch to time-related optimizations. If you just want a relative count (i.e., not absolute time) and if your machine's aren't going to be in sleep modes, you could use the RDTSC instruction directly. -- FreeBSD Volunteer, http://people.freebsd.org/~jkoshy ___ freebsd-hackers@freebsd.org mailing list http://lists.freebsd.org/mailman/listinfo/freebsd-hackers To unsubscribe, send any mail to [EMAIL PROTECTED]
