Messages in this thread | | | Date | Sat, 28 Apr 2001 21:53:01 +0200 | From | Andi Kleen <> | Subject | Re: X15 alpha release: as fast as TUX but in user space (fwd) |
| |
On Sat, Apr 28, 2001 at 05:52:42PM +0200, Ingo Molnar wrote: > > On Sat, 28 Apr 2001, Andi Kleen wrote: > > > You can also just use the cycle counter directly in most modern CPUs. > > It can be read with a single instruction. In fact modern glibc will do > > it for you when you use clock_gettime(CLOCK_PROCESS_CPUTIME_ID, ...) > > well, it's not reliable while using things like APM, so i'd not recommend > to depend on it too much.
*If* you use APM on your server boxes. Not likely even when it doesn't have more than one CPU and it can be checked at runtime.
I guess glibc could also regularly (every 10 calls or so) call regular gettimeofday to recheck synchronization; at least for a web server that potential inaccuracy would be acceptable ("best effort") and the cost of the system call is 1/10.
In x86-64 there are special vsyscalls btw to solve this problem that export a lockless kernel gettimeofday()
-Andi - To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majordomo@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
| |