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Date: Fri, 1 Sep 2023 03:17:50 -0300
From: Leonardo Bras Soares Passos <leobras@...hat.com>
To: Guo Ren <guoren@...nel.org>
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 3:58 AM Guo Ren <guoren@...nel.org> wrote:
>
> 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>
Thanks for reviewing!
>
> /*
> * 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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