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Date: Thu, 31 Aug 2023 14:58:08 +0800
From: Guo Ren <guoren@...nel.org>
To: Leonardo Bras <leobras@...hat.com>
Cc: Steven Rostedt <rostedt@...dmis.org>,
Masami Hiramatsu <mhiramat@...nel.org>,
Peter Zijlstra <peterz@...radead.org>,
Josh Poimboeuf <jpoimboe@...nel.org>,
Valentin Schneider <vschneid@...hat.com>,
"Paul E. McKenney" <paulmck@...nel.org>,
Juergen Gross <jgross@...e.com>,
Yury Norov <yury.norov@...il.com>,
Imran Khan <imran.f.khan@...cle.com>,
linux-kernel@...r.kernel.org, linux-trace-kernel@...r.kernel.org
Subject: Re: [RFC PATCH 1/1] smp: Change function signatures to use call_single_data_t
On Thu, Aug 31, 2023 at 2:31 PM Leonardo Bras <leobras@...hat.com> wrote:
>
> call_single_data_t is a size-aligned typedef of struct __call_single_data.
>
> This alignment is desirable in order to have smp_call_function*() avoid
> bouncing an extra cacheline in case of an unaligned csd, given this
> would hurt performance.
>
> Since the removal of struct request->csd in commit 660e802c76c8
> ("blk-mq: use percpu csd to remote complete instead of per-rq csd") there
> are no current users of smp_call_function*() with unaligned csd.
>
> Change every 'struct __call_single_data' function parameter to
> 'call_single_data_t', so we have warnings if any new code tries to
> introduce an smp_call_function*() call with unaligned csd.
I agree to prevent __call_single_data usage.
Reviewed-by: Guo Ren <guoren@...nel.org>
/*
* structure shares (partial) layout with struct irq_work
*/
struct __call_single_data {
struct __call_single_node node;
smp_call_func_t func;
void *info;
};
#define CSD_INIT(_func, _info) \
(struct __call_single_data){ .func = (_func), .info = (_info), }
/* Use __aligned() to avoid to use 2 cache lines for 1 csd */
typedef struct __call_single_data call_single_data_t
__aligned(sizeof(struct __call_single_data));
>
> Signed-off-by: Leonardo Bras <leobras@...hat.com>
> ---
> include/linux/smp.h | 2 +-
> include/trace/events/csd.h | 8 ++++----
> kernel/smp.c | 26 +++++++++++++-------------
> kernel/up.c | 2 +-
> 4 files changed, 19 insertions(+), 19 deletions(-)
>
> diff --git a/include/linux/smp.h b/include/linux/smp.h
> index 91ea4a67f8ca..e87520dc2959 100644
> --- a/include/linux/smp.h
> +++ b/include/linux/smp.h
> @@ -53,7 +53,7 @@ int smp_call_function_single(int cpuid, smp_call_func_t func, void *info,
> void on_each_cpu_cond_mask(smp_cond_func_t cond_func, smp_call_func_t func,
> void *info, bool wait, const struct cpumask *mask);
>
> -int smp_call_function_single_async(int cpu, struct __call_single_data *csd);
> +int smp_call_function_single_async(int cpu, call_single_data_t *csd);
>
> /*
> * Cpus stopping functions in panic. All have default weak definitions.
> diff --git a/include/trace/events/csd.h b/include/trace/events/csd.h
> index 67e9d01f80c2..58cc83b99c34 100644
> --- a/include/trace/events/csd.h
> +++ b/include/trace/events/csd.h
> @@ -12,7 +12,7 @@ TRACE_EVENT(csd_queue_cpu,
> TP_PROTO(const unsigned int cpu,
> unsigned long callsite,
> smp_call_func_t func,
> - struct __call_single_data *csd),
> + call_single_data_t *csd),
>
> TP_ARGS(cpu, callsite, func, csd),
>
> @@ -39,7 +39,7 @@ TRACE_EVENT(csd_queue_cpu,
> */
> DECLARE_EVENT_CLASS(csd_function,
>
> - TP_PROTO(smp_call_func_t func, struct __call_single_data *csd),
> + TP_PROTO(smp_call_func_t func, call_single_data_t *csd),
>
> TP_ARGS(func, csd),
>
> @@ -57,12 +57,12 @@ DECLARE_EVENT_CLASS(csd_function,
> );
>
> DEFINE_EVENT(csd_function, csd_function_entry,
> - TP_PROTO(smp_call_func_t func, struct __call_single_data *csd),
> + TP_PROTO(smp_call_func_t func, call_single_data_t *csd),
> TP_ARGS(func, csd)
> );
>
> DEFINE_EVENT(csd_function, csd_function_exit,
> - TP_PROTO(smp_call_func_t func, struct __call_single_data *csd),
> + TP_PROTO(smp_call_func_t func, call_single_data_t *csd),
> TP_ARGS(func, csd)
> );
>
> diff --git a/kernel/smp.c b/kernel/smp.c
> index 8455a53465af..8c714583786b 100644
> --- a/kernel/smp.c
> +++ b/kernel/smp.c
> @@ -127,7 +127,7 @@ send_call_function_ipi_mask(struct cpumask *mask)
> }
>
> static __always_inline void
> -csd_do_func(smp_call_func_t func, void *info, struct __call_single_data *csd)
> +csd_do_func(smp_call_func_t func, void *info, call_single_data_t *csd)
> {
> trace_csd_function_entry(func, csd);
> func(info);
> @@ -174,7 +174,7 @@ module_param(csd_lock_timeout, ulong, 0444);
> static atomic_t csd_bug_count = ATOMIC_INIT(0);
>
> /* Record current CSD work for current CPU, NULL to erase. */
> -static void __csd_lock_record(struct __call_single_data *csd)
> +static void __csd_lock_record(call_single_data_t *csd)
> {
> if (!csd) {
> smp_mb(); /* NULL cur_csd after unlock. */
> @@ -189,13 +189,13 @@ static void __csd_lock_record(struct __call_single_data *csd)
> /* Or before unlock, as the case may be. */
> }
>
> -static __always_inline void csd_lock_record(struct __call_single_data *csd)
> +static __always_inline void csd_lock_record(call_single_data_t *csd)
> {
> if (static_branch_unlikely(&csdlock_debug_enabled))
> __csd_lock_record(csd);
> }
>
> -static int csd_lock_wait_getcpu(struct __call_single_data *csd)
> +static int csd_lock_wait_getcpu(call_single_data_t *csd)
> {
> unsigned int csd_type;
>
> @@ -210,7 +210,7 @@ static int csd_lock_wait_getcpu(struct __call_single_data *csd)
> * the CSD_TYPE_SYNC/ASYNC types provide the destination CPU,
> * so waiting on other types gets much less information.
> */
> -static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *ts1, int *bug_id)
> +static bool csd_lock_wait_toolong(call_single_data_t *csd, u64 ts0, u64 *ts1, int *bug_id)
> {
> int cpu = -1;
> int cpux;
> @@ -276,7 +276,7 @@ static bool csd_lock_wait_toolong(struct __call_single_data *csd, u64 ts0, u64 *
> * previous function call. For multi-cpu calls its even more interesting
> * as we'll have to ensure no other cpu is observing our csd.
> */
> -static void __csd_lock_wait(struct __call_single_data *csd)
> +static void __csd_lock_wait(call_single_data_t *csd)
> {
> int bug_id = 0;
> u64 ts0, ts1;
> @@ -290,7 +290,7 @@ static void __csd_lock_wait(struct __call_single_data *csd)
> smp_acquire__after_ctrl_dep();
> }
>
> -static __always_inline void csd_lock_wait(struct __call_single_data *csd)
> +static __always_inline void csd_lock_wait(call_single_data_t *csd)
> {
> if (static_branch_unlikely(&csdlock_debug_enabled)) {
> __csd_lock_wait(csd);
> @@ -300,17 +300,17 @@ static __always_inline void csd_lock_wait(struct __call_single_data *csd)
> smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
> }
> #else
> -static void csd_lock_record(struct __call_single_data *csd)
> +static void csd_lock_record(call_single_data_t *csd)
> {
> }
>
> -static __always_inline void csd_lock_wait(struct __call_single_data *csd)
> +static __always_inline void csd_lock_wait(call_single_data_t *csd)
> {
> smp_cond_load_acquire(&csd->node.u_flags, !(VAL & CSD_FLAG_LOCK));
> }
> #endif
>
> -static __always_inline void csd_lock(struct __call_single_data *csd)
> +static __always_inline void csd_lock(call_single_data_t *csd)
> {
> csd_lock_wait(csd);
> csd->node.u_flags |= CSD_FLAG_LOCK;
> @@ -323,7 +323,7 @@ static __always_inline void csd_lock(struct __call_single_data *csd)
> smp_wmb();
> }
>
> -static __always_inline void csd_unlock(struct __call_single_data *csd)
> +static __always_inline void csd_unlock(call_single_data_t *csd)
> {
> WARN_ON(!(csd->node.u_flags & CSD_FLAG_LOCK));
>
> @@ -376,7 +376,7 @@ void __smp_call_single_queue(int cpu, struct llist_node *node)
> * for execution on the given CPU. data must already have
> * ->func, ->info, and ->flags set.
> */
> -static int generic_exec_single(int cpu, struct __call_single_data *csd)
> +static int generic_exec_single(int cpu, call_single_data_t *csd)
> {
> if (cpu == smp_processor_id()) {
> smp_call_func_t func = csd->func;
> @@ -667,7 +667,7 @@ EXPORT_SYMBOL(smp_call_function_single);
> *
> * Return: %0 on success or negative errno value on error
> */
> -int smp_call_function_single_async(int cpu, struct __call_single_data *csd)
> +int smp_call_function_single_async(int cpu, call_single_data_t *csd)
> {
> int err = 0;
>
> diff --git a/kernel/up.c b/kernel/up.c
> index a38b8b095251..df50828cc2f0 100644
> --- a/kernel/up.c
> +++ b/kernel/up.c
> @@ -25,7 +25,7 @@ int smp_call_function_single(int cpu, void (*func) (void *info), void *info,
> }
> EXPORT_SYMBOL(smp_call_function_single);
>
> -int smp_call_function_single_async(int cpu, struct __call_single_data *csd)
> +int smp_call_function_single_async(int cpu, call_single_data_t *csd)
> {
> unsigned long flags;
>
> --
> 2.42.0
>
--
Best Regards
Guo Ren
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