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MDEV-27943 Reduce overhead of attaching THD to OS thread, in threadpool

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Avoid relatively expensive THD::store_globals() for every query in the
threadpool. Use a lighter version instead, that only resets some thread
local storage variables(THD, mysys, PSI), avoids some calculationms
and caches syscall gettid (Linux only) in a thread_local variable.

Also simplify Worker_context use, with RAII.
This commit is contained in:
Vladislav Vaintroub 2022-10-11 00:07:38 +02:00
parent eae037c286
commit 15edd69ddf
1 changed files with 46 additions and 8 deletions
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54
sql/threadpool_common.cc
View file

@ -92,13 +92,13 @@ struct Worker_thread_context
PSI_thread *psi_thread;
st_my_thread_var* mysys_var;
void save()
Worker_thread_context()
{
psi_thread= PSI_CALL_get_thread();
mysys_var= my_thread_var;
}
void restore()
~Worker_thread_context()
{
PSI_CALL_set_thread(psi_thread);
set_mysys_var(mysys_var);
@ -142,6 +142,44 @@ static inline void set_thd_idle(THD *thd)
#endif
}
/*
Per OS thread info (ID and pthread_self)
stored as TLS, because of syscall overhead
(on Linux)
*/
struct OS_thread_info
{
pthread_t self;
ssize_t stack_size;
uint32_t thread_id;
inline bool initialized() { return stack_size != 0; }
void init(ssize_t ssize)
{
#if _WIN32
self= thread_id= GetCurrentThreadId();
#else
#ifdef __NR_gettid
thread_id= (uint32) syscall(__NR_gettid);
#else
thread_id= 0;
#endif
self= pthread_self();
#endif
stack_size= ssize;
}
};
static thread_local OS_thread_info os_thread_info;
static const OS_thread_info *get_os_thread_info()
{
auto *res= &os_thread_info;
if (!res->initialized())
res->init((ssize_t) (my_thread_stack_size * STACK_DIRECTION));
return res;
}
/*
Attach/associate the connection with the OS thread,
*/
@ -154,7 +192,12 @@ static void thread_attach(THD* thd)
#endif /* WITH_WSREP */
set_mysys_var(thd->mysys_var);
thd->thread_stack=(char*)&thd;
thd->store_globals();
set_current_thd(thd);
auto tinfo= get_os_thread_info();
thd->real_id= tinfo->self;
thd->os_thread_id= tinfo->thread_id;
DBUG_ASSERT(thd->mysys_var == my_thread_var);
thd->mysys_var->stack_ends_here= thd->thread_stack + tinfo->stack_size;
PSI_CALL_set_thread(thd->get_psi());
mysql_socket_set_thread_owner(thd->net.vio->mysql_socket);
}
@ -179,7 +222,6 @@ void tp_callback(TP_connection *c)
DBUG_ASSERT(c);
Worker_thread_context worker_context;
worker_context.save();
THD *thd= c->thd;
@ -212,7 +254,6 @@ retry:
thd->async_state.m_state = thd_async_state::enum_async_state::RESUMED;
goto retry;
}
worker_context.restore();
return;
case DISPATCH_COMMAND_CLOSE_CONNECTION:
/* QUIT or an error occurred. */
@ -231,8 +272,6 @@ retry:
c->state= TP_STATE_IDLE;
if (c->start_io())
goto error;
worker_context.restore();
return;
error:
@ -242,7 +281,6 @@ error:
threadpool_remove_connection(thd);
}
delete c;
worker_context.restore();
}