On 8/23/2023 5:03 PM, Tyler Retzlaff wrote: > On Wed, Aug 23, 2023 at 10:19:39AM +0100, Ferruh Yigit wrote: >> On 8/22/2023 11:30 PM, Konstantin Ananyev wrote: >>> 18/08/2023 14:48, Bruce Richardson пишет: >>>> On Fri, Aug 18, 2023 at 02:25:14PM +0100, Ferruh Yigit wrote: >>>>> On 8/17/2023 3:18 PM, Konstantin Ananyev wrote: >>>>>> >>>>>>>> Caution: This message originated from an External Source. Use >>>>>>>> proper caution >>>>>>>> when opening attachments, clicking links, or responding. >>>>>>>> >>>>>>>> >>>>>>>> On Wed, Aug 16, 2023 at 11:59:59AM -0700, Sivaprasad Tummala wrote: >>>>>>>>> mwaitx allows EPYC processors to enter a implementation dependent >>>>>>>>> power/performance optimized state (C1 state) for a specific >>>>>>>>> period or >>>>>>>>> until a store to the monitored address range. >>>>>>>>> >>>>>>>>> Signed-off-by: Sivaprasad Tummala <sivaprasad.tumm...@amd.com> >>>>>>>>> Acked-by: Anatoly Burakov <anatoly.bura...@intel.com> >>>>>>>>> --- >>>>>>>>> lib/eal/x86/rte_power_intrinsics.c | 77 >>>>>>>>> +++++++++++++++++++++++++----- >>>>>>>>> 1 file changed, 66 insertions(+), 11 deletions(-) >>>>>>>>> >>>>>>>>> diff --git a/lib/eal/x86/rte_power_intrinsics.c >>>>>>>>> b/lib/eal/x86/rte_power_intrinsics.c >>>>>>>>> index 6eb9e50807..b4754e17da 100644 >>>>>>>>> --- a/lib/eal/x86/rte_power_intrinsics.c >>>>>>>>> +++ b/lib/eal/x86/rte_power_intrinsics.c >>>>>>>>> @@ -17,6 +17,60 @@ static struct power_wait_status { >>>>>>>>> volatile void *monitor_addr; /**< NULL if not currently >>>>>>>>> sleeping >>>>>>>>> */ } __rte_cache_aligned wait_status[RTE_MAX_LCORE]; >>>>>>>>> >>>>>>>>> +/** >>>>>>>>> + * These functions uses UMONITOR/UMWAIT instructions and will >>>>>>>>> enter C0.2 >>>>>>>> state. >>>>>>>>> + * For more information about usage of these instructions, please >>>>>>>>> +refer to >>>>>>>>> + * Intel(R) 64 and IA-32 Architectures Software Developer's Manual. >>>>>>>>> + */ >>>>>>>>> +static void intel_umonitor(volatile void *addr) { >>>>>>>>> + /* UMONITOR */ >>>>>>>>> + asm volatile(".byte 0xf3, 0x0f, 0xae, 0xf7;" >>>>>>>>> + : >>>>>>>>> + : "D"(addr)); >>>>>>>>> +} >>>>>>>>> + >>>>>>>>> +static void intel_umwait(const uint64_t timeout) { >>>>>>>>> + const uint32_t tsc_l = (uint32_t)timeout; >>>>>>>>> + const uint32_t tsc_h = (uint32_t)(timeout >> 32); >>>>>>>>> + /* UMWAIT */ >>>>>>>>> + asm volatile(".byte 0xf2, 0x0f, 0xae, 0xf7;" >>>>>>>>> + : /* ignore rflags */ >>>>>>>>> + : "D"(0), /* enter C0.2 */ >>>>>>>>> + "a"(tsc_l), "d"(tsc_h)); } >>>>>>>> >>>>>>>> question and perhaps Anatoly Burakov can chime in with expertise. >>>>>>>> >>>>>>>> gcc/clang have built-in intrinsics for umonitor and umwait i >>>>>>>> believe as per our other >>>>>>>> thread of discussion is there a benefit to also providing inline >>>>>>>> assembly over just >>>>>>>> using the intrinsics? I understand that the intrinsics may not >>>>>>>> exist for the monitorx >>>>>>>> and mwaitx below so it is probably necessary for amd. >>>>>>>> >>>>>>>> so the suggestion here is when they are available just use the >>>>>>>> intrinsics. >>>>>>>> >>>>>>>> thanks >>>>>>>> >>>>>>> The gcc built-in functions >>>>>>> __builtin_ia32_monitorx()/__builtin_ia32_mwaitx are available only >>>>>>> when -mmwaitx >>>>>>> is used specific for AMD platforms. On generic builds, these >>>>>>> built-ins are not available and hence inline >>>>>>> assembly is required here. >>>>>> >>>>>> Ok... but we can probably put them into a separate .c file that will >>>>>> be compiled with that specific flag? >>>>>> Same thing can be probably done for Intel specific instructions. >>>>>> In general, I think it is much more preferable to use built-ins vs >>>>>> inline assembly >>>>>> (if possible off-course). >>>>>> >>>>> >>>>> We don't compile different set of files for AMD and Intel, but there are >>>>> runtime checks, so putting into separate file is not much different. >>> >>> Well, we probably don't compile .c files for particular vendor, but we >>> definitely do compile some .c files for particular ISA extensions. >>> Let say there are files in lib/acl that requires various '-mavx512*' >>> flags, same for other libs and PMDs. >>> So still not clear to me why same approach can't be applied to >>> power_instrincts.c? >>> >>>>> >>>>> It may be an option to always enable compiler flag (-mmwaitx), I think >>>>> it won't hurt other platforms but I am not sure about implications of >>>>> this to other platforms (what was the motivation for the compiler guys >>>>> to enable these build-ins with specific flag?). >>>>> >>>>> Also this requires detecting compiler that supports 'mmwaitx' or not, >>>>> etc.. >>>>> >>>> This is the biggest reason why we have in the past added support for >>>> these >>>> instructions via asm bytes rather than intrinsics. It takes a long >>>> time for >>>> end-user compilers, especially those in LTS releases, to get the >>>> necessary >>>> intrinsics. >>> >>> Yep, understand. >>> But why then we can't have both implementations? >>> Let say if WAITPKG is defined we can use builtins for >>> umonitor/umwait/tpause, otherwise we fallback to inline asm implementation. >>> Same story for MWAITX/monitorx. >>> >> >> Yes this can be done, >> it can be done either as different .c files per implementation, or as >> #ifdef in same file. >> >> But eventually asm implementation is required, as fallback, and if we >> will rely on asm implementation anyway, does it worth to have the >> additional checks to be able to use built-in intrinsic? >> >> Does it helps to comment name of the built-in function to inline >> assembly code, to document intention and another possible implementation? > > the main value of preferring intrinsics is that when they are available > they also work with msvc/windows. the msvc toolchain does not support > inline asm. so some of the targets have to use intrinsics because that's all > there is. >
How windows handles current power APIs without inline asm support, like rte_power_intrinsics.c one? Also will using both built-in and inline assembly work for Windows, since there may be compiler versions that doesn't support built-in functions, they should disable APIs altogether, and this can create a scenario that list of exposed APIs changes based on compiler version. >> >>>> Consider a user running e.g. RHEL 8, who wants to take >>>> advantages of the latest DPDK features; they should not be required to >>>> upgrade their compiler - and possibly binutils/assembler - to do so. >>>> >>>> /Bruce >>>