2019年2月24日 下午5:36于 kernel@xxxxxxxxxx写道： > > From: Wang Xuerui <wangxuerui@xxxxxxxxx> > > Hi, > > This is my WIP patchset to add support for using the on-chip ExtCC > (external counter) register as clocksource, to boost the real-time > performance on Loongson platform. I'm posting this to solicit comments > and get some of the unresolved questions answered. Hi Xuerui Thanks a lot for your works, however, the ExtCC can be influenced by the frequency of CPU core, and we have cpufreq working on Loongson-3 processors, so you should mark it conflict with cpufreq driver. And as far as I know, ExtCC is even not synchronous between different cores. I'd prefer to use gs3_HPT(0x3ff00408) register to implement this feather. Also it can be accessed from all the nodes, and the clock comes from "node clock" which will not effected by core frequency. > > * I don't have access to multi-socket ccNUMA Loongson boards. The code > most certainly doesn't work on such hardware, so either someone with > expertise would teach me how to do this, or get this done on their > own. > * I'm not sure of the pipeline behavior of the rdhwr instruction used. > The current implementation has a sync (roughly the x86 way), and I'm > not sure if it can be safely omitted, or even moved into the delay > slot on return. > * Clock skew can be a concern, but it seems there's no generic mechanism > for clocksource calibration. The x86 code has one supporting PIT/HPET- > based calibration, but that code never got extracted to common > framework. > * The VDSO performance seems very bad comparing to x86, even after > adjusting for the cycle frequency difference. But I haven't thoroughly > profiled this and perhaps won't have enough spare time for doing so > (kernel work isn't part of my day job). So maybe someone could > provide some hints in this area? > > Can only come up with so many points for now; I'll add if more ideas > turn up. > > P.S. I have to change to my personal address for outgoing mails; my > work address is hosted on QQ Enterprise Mail, which most certainly is > blocked altogether by linux-mips.org. > > Wang Xuerui (2): > MIPS: Loongson: add extcc clocksource > MIPS: VDSO: support extcc-based timekeeping > > arch/mips/include/asm/clocksource.h | 1 + > arch/mips/include/asm/mach-loongson64/extcc.h | 26 +++++++++ > arch/mips/loongson64/Kconfig | 13 +++++ > arch/mips/loongson64/common/Makefile | 5 ++ > arch/mips/loongson64/common/extcc.c | 54 +++++++++++++++++++ > arch/mips/loongson64/common/time.c | 7 +++ > arch/mips/vdso/gettimeofday.c | 8 +++ > 7 files changed, 114 insertions(+) > create mode 100644 arch/mips/include/asm/mach-loongson64/extcc.h > create mode 100644 arch/mips/loongson64/common/extcc.c > > -- > 2.20.1 >
