[dpdk-dev] [PATCH v8 2/6] eal: add the APIs to wait until equal
Gavin Hu (Arm Technology China)
Gavin.Hu at arm.com
Tue Oct 22 18:05:59 CEST 2019
> -----Original Message-----
> From: David Marchand <david.marchand at redhat.com>
> Sent: Tuesday, October 22, 2019 6:17 PM
> To: Ananyev, Konstantin <konstantin.ananyev at intel.com>
> Cc: Gavin Hu (Arm Technology China) <Gavin.Hu at arm.com>; dev
> <dev at dpdk.org>; nd <nd at arm.com>; thomas at monjalon.net; Stephen
> Hemminger <stephen at networkplumber.org>; hemant.agrawal at nxp.com;
> jerinj at marvell.com; Pavan Nikhilesh <pbhagavatula at marvell.com>;
> Honnappa Nagarahalli <Honnappa.Nagarahalli at arm.com>; Ruifeng Wang
> (Arm Technology China) <Ruifeng.Wang at arm.com>; Phil Yang (Arm
> Technology China) <Phil.Yang at arm.com>; Steve Capper
> <Steve.Capper at arm.com>
> Subject: Re: [dpdk-dev] [PATCH v8 2/6] eal: add the APIs to wait until equal
>
> On Tue, Oct 22, 2019 at 11:37 AM Ananyev, Konstantin
> <konstantin.ananyev at intel.com> wrote:
> >
> > > > The rte_wait_until_equal_xx APIs abstract the functionality of
> > > > 'polling for a memory location to become equal to a given value'.
> > > >
> > > > Add the RTE_ARM_USE_WFE configuration entry for aarch64, disabled
> > > > by default. When it is enabled, the above APIs will call WFE instruction
> > > > to save CPU cycles and power.
> > > >
> > > > From a VM, when calling this API on aarch64, it may trap in and out to
> > > > release vCPUs whereas cause high exit latency. Since kernel 4.18.20 an
> > > > adaptive trapping mechanism is introduced to balance the latency and
> > > > workload.
> > > >
> > > > Signed-off-by: Gavin Hu <gavin.hu at arm.com>
> > > > Reviewed-by: Ruifeng Wang <ruifeng.wang at arm.com>
> > > > Reviewed-by: Steve Capper <steve.capper at arm.com>
> > > > Reviewed-by: Ola Liljedahl <ola.liljedahl at arm.com>
> > > > Reviewed-by: Honnappa Nagarahalli
> <honnappa.nagarahalli at arm.com>
> > > > Reviewed-by: Phil Yang <phil.yang at arm.com>
> > > > Acked-by: Pavan Nikhilesh <pbhagavatula at marvell.com>
> > > > Acked-by: Jerin Jacob <jerinj at marvell.com>
> > > > ---
> > > > config/arm/meson.build | 1 +
> > > > config/common_base | 5 ++
> > > > .../common/include/arch/arm/rte_pause_64.h | 26 ++++++
> > > > lib/librte_eal/common/include/generic/rte_pause.h | 93
> ++++++++++++++++++++++
> > > > 4 files changed, 125 insertions(+)
> > > >
> > > > diff --git a/config/arm/meson.build b/config/arm/meson.build
> > > > index 979018e..b4b4cac 100644
> > > > --- a/config/arm/meson.build
> > > > +++ b/config/arm/meson.build
> > > > @@ -26,6 +26,7 @@ flags_common_default = [
> > > > ['RTE_LIBRTE_AVP_PMD', false],
> > > >
> > > > ['RTE_SCHED_VECTOR', false],
> > > > + ['RTE_ARM_USE_WFE', false],
> > > > ]
> > > >
> > > > flags_generic = [
> > > > diff --git a/config/common_base b/config/common_base
> > > > index e843a21..c812156 100644
> > > > --- a/config/common_base
> > > > +++ b/config/common_base
> > > > @@ -111,6 +111,11 @@ CONFIG_RTE_MAX_VFIO_CONTAINERS=64
> > > > CONFIG_RTE_MALLOC_DEBUG=n
> > > > CONFIG_RTE_EAL_NUMA_AWARE_HUGEPAGES=n
> > > > CONFIG_RTE_USE_LIBBSD=n
> > > > +# Use WFE instructions to implement the rte_wait_for_equal_xxx APIs,
> > > > +# calling these APIs put the cores in low power state while waiting
> > > > +# for the memory address to become equal to the expected value.
> > > > +# This is supported only by aarch64.
> > > > +CONFIG_RTE_ARM_USE_WFE=n
> > > >
> > > > #
> > > > # Recognize/ignore the AVX/AVX512 CPU flags for performance/power
> testing.
> > > > diff --git a/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> b/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> > > > index 93895d3..eb8f73e 100644
> > > > --- a/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> > > > +++ b/lib/librte_eal/common/include/arch/arm/rte_pause_64.h
> > > > @@ -1,5 +1,6 @@
> > > > /* SPDX-License-Identifier: BSD-3-Clause
> > > > * Copyright(c) 2017 Cavium, Inc
> > > > + * Copyright(c) 2019 Arm Limited
> > > > */
> > >
> > > Before including generic/rte_pause.h, put a check like:
> > >
> > > #ifdef RTE_ARM_USE_WFE
> > > #define RTE_ARCH_HAS_WFE
> > > #endif
> > >
> > > #include "generic/rte_pause.h"
> > >
> > > >
> > > > #ifndef _RTE_PAUSE_ARM64_H_
> > > > @@ -17,6 +18,31 @@ static inline void rte_pause(void)
> > > > asm volatile("yield" ::: "memory");
> > > > }
> > > >
> > > > +#ifdef RTE_ARM_USE_WFE
> > > > +#define sev() { asm volatile("sev" : : : "memory") }
> > > > +#define wfe() { asm volatile("wfe" : : : "memory") }
> > > > +
> > > > +#define __WAIT_UNTIL_EQUAL(type, size, addr, expected, memorder)
> \
> > > > +__rte_experimental \
> > >
> > > The experimental tag is unnecessary here.
> > > We only need it in the function prototype (in the generic header).
> > >
> > > > +static __rte_always_inline void \
> > > > +rte_wait_until_equal_##size(volatile type * addr, type expected,\
> > > > +int memorder) \
> > > > +{ \
> > > > + if (__atomic_load_n(addr, memorder) != expected) { \
> > > > + sev(); \
> > > > + do { \
> > > > + wfe(); \
> > > > + } while (__atomic_load_n(addr, memorder) != expected); \
> > > > + } \
> > > > +}
> > > > +__WAIT_UNTIL_EQUAL(uint16_t, 16, addr, expected, memorder)
> > > > +__WAIT_UNTIL_EQUAL(uint32_t, 32, addr, expected, memorder)
> > > > +__WAIT_UNTIL_EQUAL(uint64_t, 64, addr, expected, memorder)
> > > > +
> > > > +#undef __WAIT_UNTIL_EQUAL
> >
> > Might be instead of defining/undefining these macros, just
> > define explicitly these 3 functions?
> > Now they are really small, so I think it would be an easier/cleaner way.
> > Yes, a bit of code duplication, but as I said they are really small now.
> > Same thought about generic version.
>
> I don't really like those macros defining inlines either.
> I am fine with this little duplication, so +1 from me.
>
>
> >
> > >
> > > Missing #undef on sev and wfe macros.
> >
> > Actually should we undefine them?
> > Or should we add rte_ prefix (which is needed anyway I suppose)
> > and have them always defined?
> > Might be you can reuse them in other arm specific places too (spinlock,
> rwlock, etc.)
> > Actually probably it is possible to make them either emiting a proper
> instructions or NOP,
> > then you'll need RTE_ARM_USE_WFE only around these macros.
>
> Interesting idea, but only if it gets used in this series.
> I don't want to see stuff that will not be used later.
>
> >
> > I.E
> >
> > #ifdef RTE_ARM_USE_WFE
> > #define rte_sev() { asm volatile("sev" : : : "memory") }
> > #define rte_wfe() { asm volatile("wfe" : : : "memory") }
> > #else
> > static inline void rte_sev(void)
> > {
> > }
> > static inline void rte_wfe(void)
> > {
> > rte_pause();
> > }
> > #endif
> >
> > And then just one common version of _wait_ functios:
> >
> > static __rte_always_inline void \
> > rte_wait_until_equal_32(volatile type * addr, type expected, int
> memorder)
> > { \
> > if (__atomic_load_n(addr, memorder) != expected) {
> > rte_sev();
> > do {
> > rte_wfe();
> > } while (__atomic_load_n(addr, memorder) != expected);
> > }
> > }
> >
> >
>
> [snip]
>
> > > Here, change this check to:
> > >
> > > #ifndef RTE_ARCH_HAS_WFE
> > >
> > >
> > > > +#ifndef RTE_ARM_USE_WFE
> >
> > Might be something arch neutral in name here?
> > RTE_WAIT_UNTIL_EQUAL_ARCH_DEFINED or so?
>
> Yes, better than my suggestion.
>
>
> Gavin, I noticed that you added a #ifndef ARM in the generic
> rte_spinlock.h header later in this series.
> Please, can you think of a way to avoid this?
> Maybe applying the same pattern to the spinlock?
David, I will look into this and other comments, and fix them in v9, thanks for all your comments!
/Gavin
>
> Thanks.
>
> --
> David Marchand
More information about the dev
mailing list