On Tue, Dec 11, 2012 at 11:27 AM, John Stultz <john.stu...@linaro.org> wrote: > On 12/11/2012 08:11 AM, stef...@seibold.net wrote: >> >> From: Stefani Seibold <stef...@seibold.net> >> >> This small patch add the functions vdso_gettimeofday(), >> vdso_clock_gettime() >> and vdso_time() support to the VDSO for x86 32-bit kernels. >> >> The reason to do this was to get a fast reliable time stamp. Many >> developers >> uses TSC to get a fast time time stamp, without knowing the pitfalls. VDSO >> time functions a fast and reliable way, because the kernel knows the best >> time >> source and the P- and C-state of the CPU. > > Very cool. There have been similar implementations of this patch over the > years, but they were all bit more hackish then this. > > > >> For x86 the vclock_gettime.c currently supports only the HPET and TSC >> timer, >> the ACPI timer should be easily to add with an other patch. > > Although the ACPI PM timer requires port-io which would need tweaking to > allow normal users to access it. And I'm not sure if the performance would > be much improved, as the port-io probably dominates the performance cost. >
I'd actually advocate going the other way and removing hpet vdso support. Last time I benchmarked this, a syscall took about 20ns on my box, and reading the hpet counter took about 750ns, giving approximately no gain to the hpet-via-vdso optimization. --Andy -- To unsubscribe from this list: send the line "unsubscribe linux-kernel" in the body of a message to majord...@vger.kernel.org More majordomo info at http://vger.kernel.org/majordomo-info.html Please read the FAQ at http://www.tux.org/lkml/
