From: "Morten Brørup" <mb@smartsharesystems.com>
To: "Tyler Retzlaff" <roretzla@linux.microsoft.com>,
<thomas@monjalon.net>, <bruce.richardson@intel.com>
Cc: dev@dpdk.org, techboard@dpdk.org,
"Honnappa Nagarahalli" <honnappa.nagarahalli@arm.com>,
"Ruifeng Wang" <ruifeng.wang@arm.com>,
"Jerin Jacob" <jerinj@marvell.com>,
"Sunil Kumar Kori" <skori@marvell.com>,
"Mattias Rönnblom" <mattias.ronnblom@ericsson.com>,
"Joyce Kong" <joyce.kong@arm.com>,
"David Christensen" <drc@linux.vnet.ibm.com>,
"Konstantin Ananyev" <konstantin.v.ananyev@yandex.ru>,
"David Hunt" <david.hunt@intel.com>,
"David Marchand" <david.marchand@redhat.com>
Subject: RE: [PATCH v2 2/6] eal: adapt EAL to present rte optional atomics API
Date: Wed, 16 Aug 2023 22:13:22 +0200 [thread overview]
Message-ID: <98CBD80474FA8B44BF855DF32C47DC35D87B0F@smartserver.smartshare.dk> (raw)
In-Reply-To: <20230814174706.GB12422@linuxonhyperv3.guj3yctzbm1etfxqx2vob5hsef.xx.internal.cloudapp.net>
> From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> Sent: Monday, 14 August 2023 19.47
>
> On Mon, Aug 14, 2023 at 10:00:49AM +0200, Morten Brørup wrote:
> > > From: Tyler Retzlaff [mailto:roretzla@linux.microsoft.com]
> > > Sent: Friday, 11 August 2023 19.32
> > >
> > > Adapt the EAL public headers to use rte optional atomics API instead
> of
> > > directly using and exposing toolchain specific atomic builtin
> intrinsics.
> > >
> > > Signed-off-by: Tyler Retzlaff <roretzla@linux.microsoft.com>
> > > ---
> >
> > [...]
> >
>
> will fix the comments identified.
>
> >
> > [...]
> >
> > > --- a/lib/eal/include/generic/rte_spinlock.h
> > > +++ b/lib/eal/include/generic/rte_spinlock.h
> > > @@ -29,7 +29,7 @@
> > > * The rte_spinlock_t type.
> > > */
> > > typedef struct __rte_lockable {
> > > - volatile int locked; /**< lock status 0 = unlocked, 1 = locked */
> > > + volatile int __rte_atomic locked; /**< lock status 0 = unlocked, 1
> =
> > > locked */
> >
> > I think __rte_atomic should be before the type:
> > volatile __rte_atomic int locked; /**< lock status [...]
> > Alternatively (just mentioning it, I know we don't use this form):
> > volatile __rte_atomic(int) locked; /**< lock status [...]
> >
> > Thinking of where you would put "const" might help.
Regarding "const", I use the mental trick of reading from right-to-left when pointers are involved, e.g.:
const int * * const x;
----5---- 4 3 --2-- 1
x(1) is a const(2) pointer(3) to a pointer(4) to a const int(5).
And yes, treating "const int" as one word is cheating... formally it should be "int" "const", i.e. the reverse order; but that is not the convention, so I have learned to accept it.
> >
> > Maybe your order is also correct, so it is a matter of preference.
>
> so for me what you suggest is the canonical convention for c and i did
> initially try to make the change with this convention but ran into
> trouble when using the keyword in a context used as a type specifier
> and the type was incomplete.
>
> the rte_mcslock is a good example for illustration.
>
> // original struct
> typedef struct rte_mcslock {
> struct rte_mcslock *next;
> ...
> };
>
> it simply doesn't work / won't compile (at least with clang) which is
> what drove me to use the less-often used syntax.
>
> typedef struct rte_mcslock {
> _Atomic struct rte_mcslock *next;
> ...
> };
>
> In file included from ../app/test/test_mcslock.c:19:
> ..\lib\eal\include\rte_mcslock.h:36:2: error: _Atomic cannot be
> applied
> to incomplete type 'struct rte_mcslock'
> _Atomic struct rte_mcslock *next;
> ^
> ..\lib\eal\include\rte_mcslock.h:35:16: note: definition of 'struct
> rte_mcslock' is not complete until the closing '}'
> typedef struct rte_mcslock {
> ^
> 1 error generated.
>
> so i ended up choosing to use a single syntax by convention consistently
> rather than using one for the exceptional case and one everywhere else.
>
> i think (based on our other thread of discussion) i would recommend we
> use adopt and require the use of the _Atomic(T) macro to disambiguate it
> also has the advantage of not being churned later when we can do c++23.
>
> // using macro
> typedef struct rte_mcslock {
> _Atomic(struct rte_mcslock *) next;
This makes it an atomic pointer. Your example above tried making the struct rts_mcslock atomic. Probably what you wanted was:
typedef struct rte_mcslock {
struct rte_mcslock * _Atomic next;
...
};
Like "const", the convention should be putting it before any type, but after the "*" for pointers.
I suppose clang doesn't accept applying _Atomic to incomplete types, regardless where you put it... I.e. this should also fail, I guess:
typedef struct rte_mcslock {
struct rte_mcslock _Atomic * next;
...
};
> ...
> };
>
> this is much easier at a glance to know when the specified type is the T
> or the T * similarly in parameter lists it becomes more clear too.
>
> e.g.
> void foo(int *v)
>
> that it is either void foo(_Atomic(int) *v) or void foo(_Atomic(int *)
> v) becomes
> much clearer without having to do mental gymnastics.
The same could be said about making "const" clearer:
void foo(const(int) * v) instead of void foo(const int * v), and
void foo(const(int *) v) instead of void foo(int * const v).
Luckily, we don't need toolchain specific handling of "const", so let's just leave that the way it is. :-)
>
> so i propose we retain
>
> #define __rte_atomic _Atomic
>
> allow it to be used in contexts where we need a type-qualifier.
> note:
> most of the cases where _Atomic is used as a type-qualifier it
> is a red flag that we are sensitive to an implementation detail
> of the compiler. in time i hope most of these will go away as we
> remove deprecated rte_atomic_xx apis.
>
> but also introduce the following macro
>
> #define RTE_ATOMIC(type) _Atomic(type)
> require it be used in the contexts that we are using it as a type-
> specifier.
>
> if folks agree with this please reply back positively and i'll update
> the series. feel free to propose alternate names or whatever, but sooner
> than later so i don't have to churn things too much :)
+1 to Tyler's updated proposal, with macro names as suggested.
If anyone disagrees, please speak up soon!
If in doubt, please read https://en.cppreference.com/w/c/language/atomic carefully. It says:
(1) _Atomic(type-name) (since C11): Use as a type specifier; this designates a new atomic type.
(2) _Atomic type-name (since C11): Use as a type qualifier; this designates the atomic version of type-name. In this role, it may be mixed with const, volatile, and restrict, although unlike other qualifiers, the atomic version of type-name may have a different size, alignment, and object representation.
NB: I hadn't noticed this before, otherwise I had probably suggested using _Atomic(T) earlier on. We learn something new every day. :-)
>
> thanks!
Sorry about the late response, Tyler. Other work prevented me from setting aside coherent time to review your updated proposal.
>
> >
> > The DPDK coding style guidelines doesn't mention where to place
> "const", but looking at the code, it seems to use "const unsigned int"
> and "const char *".
>
> we probably should document it as a convention and most likely we should
> adopt what is already in use more commonly.
+1, but not as part of this series. :-)
next prev parent reply other threads:[~2023-08-16 20:13 UTC|newest]
Thread overview: 82+ messages / expand[flat|nested] mbox.gz Atom feed top
2023-08-11 1:31 [PATCH 0/6] RFC optional rte optional stdatomics API Tyler Retzlaff
2023-08-11 1:31 ` [PATCH 1/6] eal: provide rte stdatomics optional atomics API Tyler Retzlaff
2023-08-11 8:56 ` Bruce Richardson
2023-08-11 9:42 ` Morten Brørup
2023-08-11 15:54 ` Tyler Retzlaff
2023-08-14 9:04 ` Morten Brørup
2023-08-11 1:31 ` [PATCH 2/6] eal: adapt EAL to present rte " Tyler Retzlaff
2023-08-11 1:31 ` [PATCH 3/6] eal: add rte atomic qualifier with casts Tyler Retzlaff
2023-08-11 1:31 ` [PATCH 4/6] distributor: adapt for EAL optional atomics API changes Tyler Retzlaff
2023-08-11 1:32 ` [PATCH 5/6] bpf: " Tyler Retzlaff
2023-08-11 1:32 ` [PATCH 6/6] devtools: forbid new direct use of GCC atomic builtins Tyler Retzlaff
2023-08-11 8:57 ` Bruce Richardson
2023-08-11 9:51 ` Morten Brørup
2023-08-11 15:56 ` Tyler Retzlaff
2023-08-14 6:37 ` Morten Brørup
2023-08-11 17:32 ` [PATCH v2 0/6] RFC optional rte optional stdatomics API Tyler Retzlaff
2023-08-11 17:32 ` [PATCH v2 1/6] eal: provide rte stdatomics optional atomics API Tyler Retzlaff
2023-08-14 7:06 ` Morten Brørup
2023-08-11 17:32 ` [PATCH v2 2/6] eal: adapt EAL to present rte " Tyler Retzlaff
2023-08-14 8:00 ` Morten Brørup
2023-08-14 17:47 ` Tyler Retzlaff
2023-08-16 20:13 ` Morten Brørup [this message]
2023-08-16 20:32 ` Tyler Retzlaff
2023-08-11 17:32 ` [PATCH v2 3/6] eal: add rte atomic qualifier with casts Tyler Retzlaff
2023-08-14 8:05 ` Morten Brørup
2023-08-11 17:32 ` [PATCH v2 4/6] distributor: adapt for EAL optional atomics API changes Tyler Retzlaff
2023-08-14 8:07 ` Morten Brørup
2023-08-11 17:32 ` [PATCH v2 5/6] bpf: " Tyler Retzlaff
2023-08-14 8:11 ` Morten Brørup
2023-08-11 17:32 ` [PATCH v2 6/6] devtools: forbid new direct use of GCC atomic builtins Tyler Retzlaff
2023-08-14 8:12 ` Morten Brørup
2023-08-16 19:19 ` [PATCH v3 0/6] RFC optional rte optional stdatomics API Tyler Retzlaff
2023-08-16 19:19 ` [PATCH v3 1/6] eal: provide rte stdatomics optional atomics API Tyler Retzlaff
2023-08-16 20:55 ` Morten Brørup
2023-08-16 21:04 ` Tyler Retzlaff
2023-08-16 21:08 ` Morten Brørup
2023-08-16 21:10 ` Tyler Retzlaff
2023-08-16 19:19 ` [PATCH v3 2/6] eal: adapt EAL to present rte " Tyler Retzlaff
2023-08-16 19:19 ` [PATCH v3 3/6] eal: add rte atomic qualifier with casts Tyler Retzlaff
2023-08-16 19:19 ` [PATCH v3 4/6] distributor: adapt for EAL optional atomics API changes Tyler Retzlaff
2023-08-16 19:19 ` [PATCH v3 5/6] bpf: " Tyler Retzlaff
2023-08-16 19:19 ` [PATCH v3 6/6] devtools: forbid new direct use of GCC atomic builtins Tyler Retzlaff
2023-08-16 21:38 ` [PATCH v4 0/6] RFC optional rte optional stdatomics API Tyler Retzlaff
2023-08-16 21:38 ` [PATCH v4 1/6] eal: provide rte stdatomics optional atomics API Tyler Retzlaff
2023-08-17 11:45 ` Morten Brørup
2023-08-17 19:09 ` Tyler Retzlaff
2023-08-18 6:55 ` Morten Brørup
2023-08-16 21:38 ` [PATCH v4 2/6] eal: adapt EAL to present rte " Tyler Retzlaff
2023-08-16 21:38 ` [PATCH v4 3/6] eal: add rte atomic qualifier with casts Tyler Retzlaff
2023-08-16 21:38 ` [PATCH v4 4/6] distributor: adapt for EAL optional atomics API changes Tyler Retzlaff
2023-08-16 21:38 ` [PATCH v4 5/6] bpf: " Tyler Retzlaff
2023-08-16 21:38 ` [PATCH v4 6/6] devtools: forbid new direct use of GCC atomic builtins Tyler Retzlaff
2023-08-17 11:57 ` Morten Brørup
2023-08-17 19:14 ` Tyler Retzlaff
2023-08-18 7:13 ` Morten Brørup
2023-08-22 18:14 ` Tyler Retzlaff
2023-08-17 21:42 ` [PATCH v5 0/6] optional rte optional stdatomics API Tyler Retzlaff
2023-08-17 21:42 ` [PATCH v5 1/6] eal: provide rte stdatomics optional atomics API Tyler Retzlaff
2023-08-17 21:42 ` [PATCH v5 2/6] eal: adapt EAL to present rte " Tyler Retzlaff
2023-08-17 21:42 ` [PATCH v5 3/6] eal: add rte atomic qualifier with casts Tyler Retzlaff
2023-08-17 21:42 ` [PATCH v5 4/6] distributor: adapt for EAL optional atomics API changes Tyler Retzlaff
2023-08-17 21:42 ` [PATCH v5 5/6] bpf: " Tyler Retzlaff
2023-08-17 21:42 ` [PATCH v5 6/6] devtools: forbid new direct use of GCC atomic builtins Tyler Retzlaff
2023-08-21 22:27 ` [PATCH v5 0/6] optional rte optional stdatomics API Konstantin Ananyev
2023-08-22 21:00 ` [PATCH v6 0/6] rte atomics API for optional stdatomic Tyler Retzlaff
2023-08-22 21:00 ` [PATCH v6 1/6] eal: provide rte stdatomics optional atomics API Tyler Retzlaff
2023-09-28 8:06 ` Thomas Monjalon
2023-09-29 8:04 ` David Marchand
2023-09-29 8:54 ` Morten Brørup
2023-09-29 9:02 ` David Marchand
2023-09-29 9:26 ` Bruce Richardson
2023-09-29 9:34 ` David Marchand
2023-09-29 10:26 ` Thomas Monjalon
2023-09-29 11:38 ` David Marchand
2023-09-29 11:51 ` Thomas Monjalon
2023-08-22 21:00 ` [PATCH v6 2/6] eal: adapt EAL to present rte " Tyler Retzlaff
2023-08-22 21:00 ` [PATCH v6 3/6] eal: add rte atomic qualifier with casts Tyler Retzlaff
2023-08-22 21:00 ` [PATCH v6 4/6] distributor: adapt for EAL optional atomics API changes Tyler Retzlaff
2023-08-22 21:00 ` [PATCH v6 5/6] bpf: " Tyler Retzlaff
2023-08-22 21:00 ` [PATCH v6 6/6] devtools: forbid new direct use of GCC atomic builtins Tyler Retzlaff
2023-08-29 15:57 ` [PATCH v6 0/6] rte atomics API for optional stdatomic Tyler Retzlaff
2023-09-29 14:09 ` David Marchand
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