> -----Original Message----- > From: Ferruh Yigit <[email protected]> > Sent: Tuesday, January 11, 2022 9:46 PM > To: Ashwin Sekhar Thalakalath Kottilveetil <[email protected]>; > [email protected]; Honnappa Nagarahalli <[email protected]>; > Ruifeng Wang <[email protected]> > Cc: Nithin Kumar Dabilpuram <[email protected]>; > [email protected]; Sunil Kumar Kori <[email protected]>; Satha > Koteswara Rao Kottidi <[email protected]>; Pavan Nikhilesh > Bhagavatula <[email protected]>; Kiran Kumar Kokkilagadda > <[email protected]>; Satheesh Paul <[email protected]>; > Anoob Joseph <[email protected]>; Akhil Goyal <[email protected]> > Subject: Re: [EXT] Re: [PATCH] common/cnxk: use cas with release semantics > for batch alloc > > On 1/11/2022 12:26 PM, Ashwin Sekhar Thalakalath Kottilveetil wrote: > > CAS is compare and swap. CASL is compare and swap with release > semantics. > > > > What does 'release semantics' mean? What is functional difference in both?
'release semantics' is semantics in memory ordering for store operations. It ensures store-store ordering. And some comments below. > > > But on CNXK platform, the functionality of CAS* instructions is completely > different when it is done to specific addresses. These APIs are meant for use > for such special cases. These cannot be made ARM generic. > > > > Ashwin Sekhar T K > > > >> -----Original Message----- > >> From: Ferruh Yigit <[email protected]> > >> Sent: Tuesday, January 11, 2022 5:42 PM > >> To: Ashwin Sekhar Thalakalath Kottilveetil <[email protected]>; > >> [email protected]; Honnappa Nagarahalli <[email protected]>; > >> Ruifeng Wang (Arm Technology China) <[email protected]> > >> Cc: Nithin Kumar Dabilpuram <[email protected]>; Jerin Jacob > >> Kollanukkaran <[email protected]>; Sunil Kumar Kori > >> <[email protected]>; Satha Koteswara Rao Kottidi > >> <[email protected]>; Pavan Nikhilesh Bhagavatula > >> <[email protected]>; Kiran Kumar Kokkilagadda > >> <[email protected]>; Satheesh Paul <[email protected]>; > >> Anoob Joseph <[email protected]>; Akhil Goyal <[email protected]> > >> Subject: [EXT] Re: [PATCH] common/cnxk: use cas with release > >> semantics for batch alloc > >> > >> External Email > >> > >> --------------------------------------------------------------------- > >> - On 1/11/2022 12:08 PM, Ferruh Yigit wrote: > >>> On 11/30/2021 5:45 AM, Ashwin Sekhar T K wrote: > >>>> Before issuing the batch alloc, we clear the first word of cache > >>>> lines so that NPA can update the status. Make sure that this line > >>>> clear is flushed before the batch alloc is issued. > >>>> > >>>> Signed-off-by: Ashwin Sekhar T K <[email protected]> > >>>> --- > >>>> drivers/common/cnxk/roc_io.h | 12 ++++++++++++ > >>>> drivers/common/cnxk/roc_io_generic.h | 9 +++++++++ > >>>> drivers/common/cnxk/roc_npa.h | 2 +- > >>>> 3 files changed, 22 insertions(+), 1 deletion(-) > >>>> > >>>> diff --git a/drivers/common/cnxk/roc_io.h > >>>> b/drivers/common/cnxk/roc_io.h index fe5f7f46d0..4f15503c29 100644 > >>>> --- a/drivers/common/cnxk/roc_io.h > >>>> +++ b/drivers/common/cnxk/roc_io.h > >>>> @@ -78,6 +78,18 @@ roc_atomic64_cas(uint64_t compare, uint64_t > >> swap, > >>>> int64_t *ptr) > >>>> return compare; > >>>> } > >>>> +static __plt_always_inline uint64_t roc_atomic64_casl(uint64_t > >>>> +compare, uint64_t swap, int64_t *ptr) { > >>>> + asm volatile(PLT_CPU_FEATURE_PREAMBLE > >>>> + "casl %[compare], %[swap], [%[ptr]]\n" > >>>> + : [compare] "+r"(compare) > >>>> + : [swap] "r"(swap), [ptr] "r"(ptr) > >>>> + : "memory"); > >>>> + > >>> > >>> out of curiosity, what is the "cas with release semantics"? > >>> briefly, what is the difference between 'cas' and 'casl'? > >> > >> + Honnappa & Ruifeng, Thanks Ferruh for adding me in this loop. > >> > >> Isn't this API Arm wide, instead of being cnxk specific? > >> Does it make sense to make this API for arm and cnxk use from there? Yes, CAS operation can be used Arm wide. Generally, CAS is available via __atomic_compare_exchange/_n() compiler built-ins. This is the way we use atomic in DPDK. So there is no need to add another generic API.
