RE: [PATCH v5 3/3] power: amd power monitor support

[Konstantin Ananyev <konstantin.ananyev@huawei.com>]

> > Caution: This message originated from an External Source. Use proper caution
> > when opening attachments, clicking links, or responding.
> >
> >
> > 25/08/2023 17:00, Tyler Retzlaff пишет:
> > > On Thu, Aug 24, 2023 at 10:04:42AM +0100, Ferruh Yigit wrote:
> > >> 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.tummala@amd.com>
> > >>>>>>>>>>> Acked-by: Anatoly Burakov <anatoly.burakov@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?
> > >
> > > so this is a windows vs toolchain entanglement.
> > >
> > >> 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.
> > >
> > > so I don't intend to disable apis, theres usually a way to make them
> > > work and there should not be any api changes when done correctly.
> > >
> > > windows/clang/mingw
> > >      * inline asm may be used, but for me isn't preferred
> > >
> > > windows/msvc
> > >      * intrinsics (when available)
> > >      * non-inline asm in a .s (when no intrinsics available)
> > >      * keeping in mind that the compiler version isn't tied to windows
> > >        OS release so it's easier for me to document that you need a
> > >        newer compiler arbitrarily. The periods where there are no intrinsics
> > >        end up being short-lived.
> > >
> > > I'm on the hook for windows/msvc any stickyness dealing with it ends
> > > up being my problem.
> >
> > As I can read rte_power_instrintcts.c, for each set of power instructions we have
> > related static variable: wait*_supported.
> > So if we need to support compiler that supports neither new bultins nor inline-asm,
> > then it probably possible to rearrange the code to keep these static vars equal zero
> > for such case.
> >
> Konstantin,
> I preferred to use the inline asm for the new power instructions with this patch due to:
> 1. builtins may not always available based on compiler versions
> 2. additional complexity with versioning checks

I don't think we'll need to mock with version numbers etc.
AFAIK, each such feature as corresponding define, i.e.:
If WAITPKG is defined we can use builtins for umonitor/umwait/tpause,
If MWAITX is defined we can use mwaitx/monitorx, etc.

> 3. no additional performance benefit
> As an improvement, will add builtins support globally in a separate patch later.

Works for me, as long as we wouldn't forget to do it in future. 

 
> >
> > >
> > >>
> > >>>>
> > >>>>>> 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
> > >>>>>