[dpdk-dev] [PATCH] EAL: An addition of cache line demote (CLDEMOTE) in rte_prefetch.h
Maslekar, Omkar
omkar.maslekar at intel.com
Fri Sep 11 01:30:43 CEST 2020
Hi Bruce,
>-----Original Message-----
>From: Bruce Richardson <bruce.richardson at intel.com>
>Sent: Thursday, September 10, 2020 1:55 AM
>To: Maslekar, Omkar <omkar.maslekar at intel.com>
>Cc: dev at dpdk.org; Loftus, Ciara <ciara.loftus at intel.com>
>Subject: Re: [PATCH] EAL: An addition of cache line demote (CLDEMOTE) in
>rte_prefetch.h
>
>On Wed, Sep 09, 2020 at 06:16:54PM -0700, Omkar Maslekar wrote:
>> rte_cldemote is similar to a prefetch hint - in reverse.
>> cldemote(addr) enables software to hint to hardware that line is likely to be
>shared.
>> Useful in core-to-core communications where cache-line is likely to be
>> shared. ARM and PPC implementation is provided with NOP and can be
>> added if any equivalent instructions could be used for implementation
>> on those architectures.
>>
>> Signed-off-by: Omkar Maslekar <omkar.maslekar at intel.com>
>> ---
>
>Hi Omkar,
>
>please see some review comments inline below.
>
>Regards,
>/Bruce
>
>> doc/guides/rel_notes/release_20_11.rst | 26 ++++----------------------
>> lib/librte_eal/arm/include/rte_prefetch_32.h | 5 +++++
>> lib/librte_eal/arm/include/rte_prefetch_64.h | 5 +++++
>> lib/librte_eal/include/generic/rte_prefetch.h | 7 +++++++
>> lib/librte_eal/ppc/include/rte_prefetch.h | 5 +++++
>> lib/librte_eal/x86/include/rte_prefetch.h | 9 +++++++++
>> 6 files changed, 35 insertions(+), 22 deletions(-)
>>
>> diff --git a/doc/guides/rel_notes/release_20_11.rst
>> b/doc/guides/rel_notes/release_20_11.rst
>> index df227a1..c4a4362 100644
>> --- a/doc/guides/rel_notes/release_20_11.rst
>> +++ b/doc/guides/rel_notes/release_20_11.rst
>> @@ -27,29 +27,11 @@ New Features
>> .. This section should contain new features added in this release.
>> Sample format:
>>
>> - * **Add a title in the past tense with a full stop.**
>> +Added new instruction CLDEMOTE in rte_prefetch.h.
>
>You need to prefix this with the library it is in, in this case EAL. Also, since this
>is C code, you are adding a function, not an instruction.
[I will fix these release notes]
>
>>
>> - Add a short 1-2 sentence description in the past tense.
>> - The description should be enough to allow someone scanning
>> - the release notes to understand the new feature.
>> -
>> - If the feature adds a lot of sub-features you can use a bullet list
>> - like this:
>> -
>> - * Added feature foo to do something.
>> - * Enhanced feature bar to do something else.
>> -
>> - Refer to the previous release notes for examples.
>> -
>> - Suggested order in release notes items:
>> - * Core libs (EAL, mempool, ring, mbuf, buses)
>> - * Device abstraction libs and PMDs
>> - - ethdev (lib, PMDs)
>> - - cryptodev (lib, PMDs)
>> - - eventdev (lib, PMDs)
>> - - etc
>> - * Other libs
>> - * Apps, Examples, Tools (if significant)
>
>Don't remove these lines, they are all also part of the same comment as
>below where it says "Do not overwrite or remove it" :-)
[I will revert original comment and add appropriate]
>
>> + Added a hardware hint CLDEMOTE which is similar to prefetch in
>reverse.
>> + CLDEMOTES moves the cache line to the last shared cache, where it
>expects
>> + sharing to be efficient.
>>
>
>Reading the instruction description in the Intel instruction set reference, it
>says about moving the cache line to a more remote cache-line, rather than
>guaranteeing that it goes to the last level cache. Therefore, to ensure
>compatiblity with the current spec and make it more flexible to meet any
>other hardware implementations, I suggest changing the "last shared cache
>..." to "more remote cache where sharing may be more efficient".
[I will make these changes as per suggestion and make sure it is in sync with software development manual ]
>
>> This section is a comment. Do not overwrite or remove it.
>> Also, make sure to start the actual text at the margin.
>> diff --git a/lib/librte_eal/arm/include/rte_prefetch_32.h
>> b/lib/librte_eal/arm/include/rte_prefetch_32.h
>> index e53420a..ad91edd 100644
>> --- a/lib/librte_eal/arm/include/rte_prefetch_32.h
>> +++ b/lib/librte_eal/arm/include/rte_prefetch_32.h
>> @@ -33,6 +33,11 @@ static inline void rte_prefetch_non_temporal(const
>volatile void *p)
>> rte_prefetch0(p);
>> }
>>
>> +static inline void rte_cldemote(const volatile void *p) {
>> + RTE_SET_USED(p);
>> +}
>> +
>> #ifdef __cplusplus
>> }
>> #endif
>> diff --git a/lib/librte_eal/arm/include/rte_prefetch_64.h
>> b/lib/librte_eal/arm/include/rte_prefetch_64.h
>> index fc2b391..35d278a 100644
>> --- a/lib/librte_eal/arm/include/rte_prefetch_64.h
>> +++ b/lib/librte_eal/arm/include/rte_prefetch_64.h
>> @@ -32,6 +32,11 @@ static inline void rte_prefetch_non_temporal(const
>volatile void *p)
>> asm volatile ("PRFM PLDL1STRM, [%0]" : : "r" (p)); }
>>
>> +static inline void rte_cldemote(const volatile void *p) {
>> + RTE_SET_USED(p);
>> +}
>> +
>> #ifdef __cplusplus
>> }
>> #endif
>> diff --git a/lib/librte_eal/include/generic/rte_prefetch.h
>> b/lib/librte_eal/include/generic/rte_prefetch.h
>> index 6e47bdf..89ec69c 100644
>> --- a/lib/librte_eal/include/generic/rte_prefetch.h
>> +++ b/lib/librte_eal/include/generic/rte_prefetch.h
>> @@ -51,4 +51,11 @@
>> */
>> static inline void rte_prefetch_non_temporal(const volatile void *p);
>>
>> +/**
>> + * Demote a cache line into the last shared cache level.
>
>Same comment as above. Since this will make it into the official API doxygen
>documentation, I think a bit fuller of a description would be good also.
[I will add more documentation]
More information about the dev
mailing list