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16808549 |
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17-Aug-2016 |
Konstantin Belousov <kib@FreeBSD.org> |
Implement userspace gettimeofday(2) with HPET timecounter. Right now, userspace (fast) gettimeofday(2) on x86 only works for RDTSC. For older machines, like Core2, where RDTSC is not C2/C3 invariant, and which fall to HPET hardware, this means that the call has both the penalty of the syscall and of the uncached hw behind the QPI or PCIe connection to the sought bridge. Nothing can me done against the access latency, but the syscall overhead can be removed. System already provides mappable /dev/hpetX devices, which gives straight access to the HPET registers page. Add yet another algorithm to the x86 'vdso' timehands. Libc is updated to handle both RDTSC and HPET. For HPET, the index of the hpet device to mmap is passed from kernel to userspace, index might be changed and libc invalidates its mapping as needed. Remove cpu_fill_vdso_timehands() KPI, instead require that timecounters which can be used from userspace, to provide tc_fill_vdso_timehands{,32}() methods. Merge i386 and amd64 libc/<arch>/sys/__vdso_gettc.c into one source file in the new libc/x86/sys location. __vdso_gettc() internal interface is changed to move timecounter algorithm detection into the MD code. Measurements show that RDTSC even with the syscall overhead is faster than userspace HPET access. But still, userspace HPET is three-four times faster than syscall HPET on several Core2 and SandyBridge machines. Tested by: Howard Su <howard0su@gmail.com> Sponsored by: The FreeBSD Foundation MFC after: 1 month Differential revision: https://reviews.freebsd.org/D7473
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875b8844 |
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20-Jun-2010 |
Alexander Motin <mav@FreeBSD.org> |
Implement new event timers infrastructure. It provides unified APIs for writing event timer drivers, for choosing best possible drivers by machine independent code and for operating them to supply kernel with hardclock(), statclock() and profclock() events in unified fashion on various hardware. Infrastructure provides support for both per-CPU (independent for every CPU core) and global timers in periodic and one-shot modes. MI management code at this moment uses only periodic mode, but one-shot mode use planned for later, as part of tickless kernel project. For this moment infrastructure used on i386 and amd64 architectures. Other archs are welcome to follow, while their current operation should not be affected. This patch updates existing drivers (i8254, RTC and LAPIC) for the new order, and adds event timers support into the HPET driver. These drivers have different capabilities: LAPIC - per-CPU timer, supports periodic and one-shot operation, may freeze in C3 state, calibrated on first use, so may be not exactly precise. HPET - depending on hardware can work as per-CPU or global, supports periodic and one-shot operation, usually provides several event timers. i8254 - global, limited to periodic mode, because same hardware used also as time counter. RTC - global, supports only periodic mode, set of frequencies in Hz limited by powers of 2. Depending on hardware capabilities, drivers preferred in following orders, either LAPIC, HPETs, i8254, RTC or HPETs, LAPIC, i8254, RTC. User may explicitly specify wanted timers via loader tunables or sysctls: kern.eventtimer.timer1 and kern.eventtimer.timer2. If requested driver is unavailable or unoperational, system will try to replace it. If no more timers available or "NONE" specified for second, system will operate using only one timer, multiplying it's frequency by few times and uing respective dividers to honor hz, stathz and profhz values, set during initial setup.
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